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subunits and cytoplasmic modulatory β subunits. The differential expression and association of and β subunits seems to contribute significantly to the complexity and heterogeneity of KV channels in excitable cells, and their functional expression in heterologous systems provides a tool to study their regulation at a molecular level. Here, we have studied the effects of Kvβ1.2 coexpression on the properties of Shaker and Kv4.2 KV channel subunits, which encode rapidly inactivating A-type K+ currents, in transfected HEK293 cells. We found that Kvβ1.2 functionally associates with these two subunits, as well as with the endogenous KV channels of HEK293 cells, to modulate different properties of the heteromultimers. Kvβ1.2 accelerates the rate of inactivation of the Shaker currents, as previously described, increases significantly the amplitude of the endogenous currents, and confers sensitivity to redox modulation and hypoxia to Kv4.2 channels. Upon association with Kvβ1.2, Kv4.2 can be modified by DTT (1,4 dithiothreitol) and DTDP (2,2'-dithiodipyridine), which also modulate the low pO2 response of the Kv4.2+β channels. However, the physiological reducing agent GSH (reduced glutathione) did not mimic the effects of DTT. Finally, hypoxic inhibition of Kv4.2+β currents can be reverted by 70% in the presence of carbon monoxide and remains in cell-free patches, suggesting the presence of a hemoproteic O2 sensor in HEK293 cells and a membrane-delimited mechanism at the origin of hypoxic responses. We conclude that β subunits can modulate different properties upon association with different KV channel subfamilies; of potential relevance to understanding the molecular basis of low pO2 sensitivity in native tissues is the here described acquisition of the ability of Kv4.2+β channels to respond to hypoxia.
Key Words: potassium channels • β subunit • hypoxia
Abbreviations: GFP, green fluorescent protein; GSH, reduced glutathione; KV channel, voltage-gated K+ channel; (M)ANOVA, fully factorial analysis of variance
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subunits of KV channels that can give rise to delayed rectifier or A-type currents upon expression in heterologous systems (Chandy and Gutman, 1995
). The functional and structural diversity of the KV channels' subunits is further increased by their capacity to form functional heterotetrameric structures and to associate with modulatory β subunits (for review see Pongs, 1995; Jan and Jan, 1997). For example, association of β subunits with some members of the Shaker subfamily results in β heteromultimers with inactivation kinetics more rapid than those of the corresponding homomultimers (Rettig et al., 1994; Chouinard et al., 1995; Heinemann et al., 1995; Majumder et al., 1995; McCormack et al., 1995; Morales et al., 1995), and, even further, some of these β subunits can convert a delayed rectifier into a rapidly inactivating channel (Rettig et al., 1994; England et al., 1995; Majumder et al., 1995; Morales et al., 1995; Heinemann et al., 1996).
In some tissues, K+ currents exhibit specific properties, such as regulation by oxygen levels (Lopez-Barneo et al., 1988; Post et al., 1992; Youngson et al., 1993). It has been hypothesized that O2 sensitivity of K+ currents could be intrinsic to the channels themselves (Ruppersberg et al., 1991; Duprat et al., 1995; Weir and Archer, 1995) or, alternatively, that a membrane-bound O2 sensor or a regulatory subunit of the K+ channels confers the observed sensitivity (Gonzalez et al., 1992; Lopez-Barneo, 1994; Patel et al., 1997).
In the present work, we have used an heterologous expression system to study the association of the auxiliary subunit Kvβ1.2 (formerly Kvβ3) with some cloned KV channels and its possible contribution to the hypoxic sensitivity of the heteromultimers. The KV channels used (Shaker B and Kv4.2) express rapidly inactivating currents comparable to the oxygen-sensitive K+ currents described in some preparations (Lopez-Barneo et al., 1988; Gonzalez et al., 1992). We found subfamily-specific functional interactions between Kvβ1.2 and the different KV channels studied, so that Kvβ1.2 coexpression is able to regulate the amplitude of the endogenous HEK293 KV currents, the rate of inactivation of the Shaker currents, and the redox and oxygen sensitivity of the Kv4.2 currents. The hypoxic response of the Kv4.2+Kvβ1.2 heteromultimers was unaffected by application of reduced glutathione (GSH) in the pipette solution or in the bath, but was prevented by treatment with DTT (1,4 dithiothreitol) and restored with DTDP (2,2'-dithiodipyridine), suggesting that reduction of some, but not all, of the residues susceptible to redox modulation can disrupt the mechanism underlying the low pO2 regulation of these channels. Hypoxic inhibition was reverted by carbon monoxide (suggesting the presence of an hemoproteic O2 sensor in HEK cells) and remains in excised membrane patches, indicating that the mechanism of low pO2 inhibition is restricted to the plasma membrane.
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) with 1 µg of plasmid DNA encoding the drosophila Shaker B (H4) K+ channel subunit (into pRcRSV; Invitrogen Corp.), or the Kv4.2 K+ channel subunit (into E42c) alone or in combination with 2 µg of plasmid DNA encoding the Kvβ1.2 subunit into pREP4. In a group of experiments, the cells were only transfected with 2 µg of Kvβ1.2 subunit. In all cases, 0.2 µg of green fluorescent protein (GFP) in a CMV-promoter expression plasmid (GFPPRK5), was included to permit transfection efficiency estimates (10–40%) and to identify cells for voltage-clamp analysis (Marshall et al., 1995). Voltage-clamp recordings revealed typical inactivating currents in 100% of the cells expressing GFP. A group of control cells was obtained by analyzing the currents present in cells transfected with GFP alone or in untransfected cells. All plasmids used in this study were generously provided by Drs. E. Marban and G.F. Tomaselli (John Hopkins University, Baltimore, MD).
Electrophysiological Recordings
K+ currents were studied using either the whole-cell or the outside-out configuration of the patch-clamp technique. The holding potential was –60 or –80 mV, respectively. Isolated HEK cells were studied 1–3 d after transfection. The coverslips with the attached cells were transferred to a small recording chamber (0.2 ml) placed in the stage of an inverted microscope and perfused by gravity with (mM): 141 NaCl, 4.7 KCl, 1.2 MgCl2, 1.8 CaCl2, 10 glucose, 10 HEPES, pH 7.4 with NaOH. The bath solution was connected to ground via a 3 M KCl agar bridge and a Ag-AgCl electrode. Patch pipettes were double pulled (PP-83; Narishige Co.) and heat polished (MF-83; Narishige Co.) to resistances ranging from 1.5–3 M
for whole-cell experiments to 10–15 M for cell-free recordings when filled with a internal solution containing (mM): 125 KCl, 4 MgCl2, 10 HEPES, 10 EGTA, 5 MgATP, pH 7.2 with KOH. Hypoxia was achieved by bubbling the reservoir that fed the perfusion chamber with 100% N2. The final pO2 level in the perfusion chamber was below 10 mmHg. The time course of the fall in the pO2 was complete within 1 min of solution exchange. In selected experiments, the control solutions were also bubbled with air to exclude potential artifactual effects due to the bubbling of the solutions. Whole-cell currents were recorded using an Axopatch 200 patch-clamp amplifier, sampled at 10 and filtered at 2 kHz (–3 dB, four-pole Bessel filter). The series resistance (ranging from 4 to 10 M) was routinely compensated by 60–80%. Data were leak subtracted on line by a P/4 protocol. K+ currents from macropatches in the outside-out configuration were registered several minutes after excision and were taken as the difference between the current recorded in a 50-ms depolarizing pulse to +40 mV from a holding potential of –80 mV and the average current obtained applying four pulses to +40 mV after inactivating the K+ channels with 200-ms prepulses to the same potential. To facilitate the subtraction of capacitative transients, the potential was held at –80 mV during 1 ms between prepulse and pulse. Currents were sampled at 5 and filtered at 1 kHz. Records were digitized with a Digidata-1200 A/D converter (Axon Instruments), and stored on disk using PCLAMP version 6.02 software. All the experiments were done at room temperature (20–22°C).
Data Analysis
Analysis of the data was performed with the CLAMPFIT subroutines of the PCLAMP software and ORIGIN 4.0 software (Microcal Software, Inc.). Pooled data are expressed as mean ± SEM. Statistical comparisons between groups of data were carried out with the two-tailed Student's t test for paired or unpaired data, and values of P < 0.05 were considered statistically significant. The analysis of the differences between two groups of data when comparing more than one variable was done with a fully factorial analysis of variance [(M)ANOVA] using commercial software (SYSTAT; Systat Inc.).
Materials
DTT, DTDP, and GSH were obtained from Sigma Chemical Co. DTT and GSH were prepared fresh and dissolved in the bath or in the pipette solution, and DTDP was first dissolved in ethanol to a concentration of 500 mM, and then diluted in bath solution to a final concentration of 100 µM.
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subunit cDNA gave rise to large, rapid inactivating currents in all the cells studied (Fig. 1, B and C). Kvβ1.2 coexpression did not modify significantly the current amplitude, as shown in the averaged peak current–voltage relationships.
Effects of Kvβ1.2 on the Kinetics of the Cloned K+ Channels
It has been demonstrated that Kvβ1.2 is able to modulate the rate of inactivation of some of the members of the Shaker family when coinjected in Xenopus oocytes (England et al., 1995; Majumder et al., 1995; Morales et al., 1995). However, it is not known whether this subunit is able to functionally associate with the K+ channels of the Shal subfamily (Kv4) and modulate their electrophysiological properties. In our expression system, Kvβ1.2 also modulates the kinetics of the recombinant Shaker channels. The traces in Fig. 2 A show that β subunit coexpression accelerates the rate of inactivation and decreased the amplitude of the currents at the end of a 100-ms pulse. The inactivation time course for both Shaker and Shaker+β K+ channels was best fitted to a biexponential function with time constants that exhibited little voltage dependence. The presence of β subunit produced an acceleration of inactivation due to a significant decrease in the fast time constant at all the voltages [P = 0.02 with (M)ANOVA] and a less-pronounced decrease in the slow time constant that was not significant in our analysis (P = 0.054). However, this slow time constant is very likely distorted by the contribution of endogenous currents. Fig. 2 B shows a similar analysis of the kinetics of the Kv4.2 and Kv4.2+β recombinant channels. The time course of inactivation was also fitted to a biexponential function, but in this case it was not changed by the presence of β subunit. The same lack of effect on the activation and inactivation kinetics was observed for the endogenous channels upon association with β subunit (data not shown).
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subunits to modulate other properties of the channel. Among these other properties, we have studied their sensitivity to sulfhydryl group reagents. Chemical redox modulation has been demonstrated for different native K+ channels (Weir and Archer, 1995) as well as for several cloned K+ channel subunits (Ruppersberg et al., 1991; Duprat et al., 1995). Furthermore, a redox mechanism has been shown to modulate the effects of β subunit on the rate of inactivation of Kv1.4 K+ channels (Rettig et al., 1994; Heinemann et al., 1995). In our work, the application of the membrane-permeable reducing agent DTT or the oxidizing agent DTDP to HEK cells expressing Shaker or Shaker+β had effects similar to those reported in the aforementioned works using other redox agents. Fig. 3 A shows one of four cells in which application of 100 µM DTDP markedly decreased the rate of inactivation of the Shaker+β currents in an irreversible way, whereas treatment with 2 mM DTT had the opposite effect. As an indicator of the change in the rate of inactivation, the average modification in the amplitude of the currents at the end of a 100-ms depolarizing pulse was calculated for three more cells expressing Shaker+β channels (Fig. 3 A, inset). DTT treatment reduced the amplitude of the current at the end of the pulse by 20.85 ± 7.1%, whereas DTDP increased this amplitude by 65.5 ± 12.1% (n = 4). The same modifications in the rate of inactivation were observed in cells transfected with Shaker alone (data not shown). On the contrary, treatment with DTT or DTDP failed to modify the amplitude or the kinetics of the currents expressed in cells transfected with Kv4.2 alone (Fig. 3 B, n = 3), in agreement with previous results showing the resistance of channels of the Kv4 subfamily to treatment with other redox agents (Duprat et al., 1995). When the same experiment was carried out in Kv4.2+β-transfected cells (Fig. 3 C), we could observe that application of 2 mM DTT produced an irreversible reduction of the current amplitude without any significant change in the kinetics of the currents. Treatment with DTDP (100 µM) did not modify in a significant way the amplitude of the currents, but was able to revert the inhibition induced by DTT. Similar effects were observed in five more cells expressing Kv4.2+β channels (Fig. 3 C, inset). These results demonstrate that Kvβ1.2 is capable of associating with Kv4.2 subunits and, upon coexpression, confers sensitivity to redox modulation to the Kv4.2+β heteromultimers.
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). It is not known whether the oxygen-sensitive K+ channels have an O2 sensing domain or, alternatively, the oxygen-sensitive cells have other sensor structures that can affect channel function. To address this question, we have studied the effect of lowering pO2 on the cloned K+ currents, as well as the possible contribution of Kvβ1.2 to the O2 modulation of the channels. Fig. 4 A shows typical records obtained in depolarizing pulses to +40 mV from a holding potential of –60 mV for each channel (endogenous, Shaker, and Kv4.2) alone or in combination with Kvβ1.2. In each case, N2-equilibrated solutions were applied for 2–5 min. Hypoxia did not modify in a significant way the amplitude or the time course of the endogenous currents in the mock-transfected (n = 5) or β-transfected (n = 6) cells. The same lack of effect was observed in all cells expressing Shaker channels alone (n = 8). In cells transfected with Shaker+β, hypoxia produced a 10% reduction in the current amplitude only in one of eight cells studied (12.5%) and, in Kv4.2-transfected cells, there was a 9% reduction in the current amplitude in 2 of 13 cells (15%). However, when the effect of hypoxia was studied in Kv4.2+β-cotransfected cells, 38 of 41 cells studied (93%) showed a reduction in the peak current amplitude that ranged from 10 to 40% and averaged 15.48 ± 0.93% at +40 mV (mean ± SEM, n = 38). Even though in some of the cells low pO2 application seemed to slow down the time course of inactivation, this effect was not found to be statistically significant.
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Effects of DTT and DTDP on the Response of Kv4.2+β to Hypoxia
The association with Kvβ1.2 invests Kv4.2 channels with two new properties, sensitivity to redox modulation and responsiveness to low pO2 stimulation, making attractive the hypothesis that the redox status of the Kv4.2+β channels could be involved in the effect of hypoxia. This hypothesis was explored by studying the effect of hypoxic solutions on these channels after application of reducing or oxidizing agents. Fig. 5 A shows that application of 2 mM DTT produces an irreversible reduction of the current amplitude after which the response to hypoxia is lost. In these cells the effect of hypoxia was modified from a 13 ± 1.2% inhibition in control conditions to a 1.6 ± 0.6% inhibition after DTT treatment. The same protocol was used to study the effect of the oxidizing agent DTDP (100 µM) on the hypoxic inhibition of the channels (Fig. 5 B). In this case, we can see that DTDP did not modify the response to hypoxia of the Kv4.2+β currents (hypoxic inhibition averaged 16.1 ± 2.7% before and 14 ± 1.7% after DTDP treatment, n = 6), although it was able to recover the hypoxic response of cells previously exposed to DTT (data not shown). These results indicate that the residues of the Kv4.2+β heteromultimers sensitive to DTT and DTDP treatment are involved in the response of the channel to acute hypoxia.
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). Additionally, due to its lower membrane permeability, GSH could be helpful in indicating whether the effects are mainly due to modification of an intracellular or an extracellular site. We performed a series of experiments to explore the effect of pipette application of 5 mM GSH on the amplitude and the kinetics of Kv4.2+β currents and on their response to low pO2 exposure. Parallel experiments in the same cultures with our normal pipette solution were used as controls. We found that inclusion of 5 mM GSH in the pipette solution did not change the amplitude of the currents (the peak current at +40 mV averaged 2.57 ± 0.46 nA in control versus 2.37 ± 0.49 nA in GSH-treated cells, n = 9) nor the inactivation time course (the two time constants were 11.6 ± 2.9 and 120 ± 6 ms in control cells versus 15 ± 4 and 135 ± 10.2 ms in the presence of GSH, n = 9). When the cells were bathed in a N2-equilibrated solution, all cells in the two groups showed a reduction of the peak current amplitude, averaging 16.25 ± 1.6% in control and 16.86 ± 1.83% in GSH-treated cells. The effects of extracellular application of 5 mM GSH are shown in Fig. 6, where the peak current amplitude in depolarizing pulses to +40 mV is plotted against time. In this cell, application of a N2-equilibrated solution produced the same reduction of the current amplitude before and after bath application of GSH (23 and 22%, respectively). Treatment with 5 mM GSH reversibly decreased the amplitude and rate of inactivation of Kv4.2+β currents, but did not modify the magnitude of the effect of hypoxia. Similar results were observed in four more cells, in which the reduction produced by 5 mM GSH was somehow variable, averaging 33 ± 7%.
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), as well as in heterologous expression systems such as COS cells (Patel et al., 1997) and HEK293 cells (Fearon et al., 1999). To explore this possibility, we have studied the effect of carbon monoxide on the hypoxic response of Kv4.2+β. CO is a very inert gas that in biological systems only reacts with hemoproteins. Fig. 8 shows the effect of CO on the inhibition of Kv4.2+β currents by low pO2. Fig. 8 shows the peak current amplitudes at two different voltages obtained in a cell while perfusing with control solution (pO2 = 150 mmHg), with a hypoxic solution equilibrated with 100% N2 (pO2 < 10 mmHg), with a hypoxic solution equilibrated with a gas mixture containing 20% CO in N2 (pO2 < 10 mmHg, estimated pCO = 150 mmHg), and after returning to the control solution. We found that CO is reverting in a significant extent the inhibition observed with hypoxia with a time course even faster that the onset of hypoxic application, indicating that CO is able to successfully replace O2 at the O2-sensing molecule, albeit with smaller affinity. The same reversion was observed in 10 more cells studied, in which CO prevented or reversed by 69.5 ± 3.2% the low pO2-induced inhibition of Kv4.2+β currents, so that the average hypoxic inhibition decreased from 16.2 ± 1.4% to 5.04 ± 0.9% (Fig. 8 B).
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). The presence of endogenous subunits did not represent a problem due to the clear differences, both in amplitude and kinetics, between these endogenous currents and the currents through transfected KV channels (see Fig. 1). The significant increase in the endogenous current amplitude obtained in Kvβ1.2-transfected cells suggest that this subunit interacts with the endogenous subunits. A chaperon-like effect has been reported for several β subunits acting on specific KV channel subunits (Chouinard et al., 1995; Fink et al., 1996; Shi et al., 1996).
Studies on β subunit–mediated effects on K+ channels have been primarily focused on the modifications induced in the inactivation kinetics of the heteromultimers. These studies indicate that several β subunits (Kvβ1, Kvβ3, and the Drosophila homologue Hk) are able to increase the rate of inactivation of specific members of the Shaker subfamily that express A-type currents or convert delayed-rectifier currents into A-type currents (see INTRODUCTION). This interaction between Kvβ1 and members of the Shaker subfamily has been confirmed with immunohistochemical studies that show the association and colocalization of these -β complexes (Rhodes et al., 1995, 1997; Nakahira et al., 1996; Yu et al., 1996). It has also been reported the existence of selective interaction between both Kvβ1 and Kvβ2 and the mammalian Shal homologue Kv4.2 (Nakahira et al., 1996), but functional analysis has failed to reveal a change in the inactivation properties of the members of the Shal subfamily when coexpressed with Kvβ1 subunit (Heinemann et al., 1996; Yu et al., 1996).
In agreement with these reports, we found that coexpression with Kvβ1.2 produces a significant change in the rate of inactivation of the Shaker channels due to a decrease in the fast time constant. Besides, the fact that the acceleration of the channel inactivation by Kvβ1.2 does not reduce the peak current amplitude (Fig. 1 B) suggests that Kvβ1.2 is also increasing the surface expression of Shaker channels. Also in agreement with previous data, we found no changes in the inactivation rate of the Kv4.2 currents upon Kvβ1.2 coexpression. However, the association is functionally assessed by the acquisition by the Kv4.2+β currents of new property, namely the sensitivity to sulfhydryl group reagents (Fig. 3). Another proof of this functional association of Kv4.2 with Kvβ1.2 is the capability of Kv4.2+β currents to respond to low pO2. This response was only consistently observed in our expression system with this particular +β subunit combination, and consisted in a reversible reduction of the current amplitude upon exposure to hypoxic solutions (Figs. 4–8). One important aspect to consider regarding this effect is whether we are dealing with a metabolic or an allosteric-type mechanism. Given the speed of the effect of hypoxia, and the presence of 5 mM ATP in the intracellular solution, a direct action of hypoxia seems more likely than a response to altered cellular metabolism. Actually, hypoxic inhibition of native A-type K+ channels has been slow to occur in excised membrane patches (Ganfornina and Lopez-Barneo, 1991), and the data presented in Fig. 7, showing the same effect of hypoxia in excised patches in the absence of potential intracellular mediators, strongly suggest that the response to hypoxia is a membrane-delimited mechanism. In addition, the persistence of the low pO2 inhibition in a cell-free preparation confirms that Kv4.2 is able to coassemble with Kvβ1.2.
The modifications in the hypoxic response after application of freely membrane-permeable oxidizing and reducing agents suggest that hypoxic sensitivity can be modulated by the redox status of the channel proteins and that the same cysteine residues modified by DTT and DTDP are involved in the low pO2 regulation of the Kv4.2+β channels. However, the absence of effect of GSH when applied intracellularly argues against a role for redox modulation under physiological conditions, and also excludes the possibility that the effect of low pO2 on the Kv4.2+β channels could be attributable to the redox status of the cytoplasmic β subunits. On the other hand, extracellular GSH application does not interfere with the hypoxic response of the channel, supporting the idea that hypoxia and reducing agents can inhibit Kv4.2+β currents through different mechanisms. The fact that Shaker and Shaker+β channels are also modified by these agents, but insensitive to hypoxia, stresses out the fact that the effect of low pO2 as a physiological stimulus is not simply achieved by the reduction of a sulfhydryl group. Redox modulation of Shaker or Shaker+β currents was able to change their rate of inactivation, but none of these maneuvers rendered the channels sensitive to hypoxia (data not shown). Furthermore, in contrast with DTT effect, application of hypoxic solutions did not modify the rate of inactivation of the channels (see Fig. 4 A). These observations indicate that O2 sensing must have some specific structural requirements that seem to be achieved in our expression system by the combination of Kv4.2 subunits with Kvβ1.2 subunits. With respect to the molecular nature of the O2-sensing mechanism, there are two possibilities: first, the Kv4.2+β channels themselves are the O2-sensing devices and, second, there is some other O2-sensing molecule endogenously present in HEK293 cells (Wang and Semenza, 1993; Fearon et al., 1999) capable of interacting with Kv4.2 subunits only when a β subunit is also present. Data on the literature showing that other structurally distinct channels are also O2 sensitive in this cell line (Fearon et al., 1997; McKenna et al., 1998) support the second possibility, and data on the present study locate this O2 sensor in the plasma membrane. Since the only known targets of CO in biological systems are reduced hemoproteins with accessible iron sites, our observation that CO is able to interact with this putative O2 sensor, replacing O2 and preventing the inhibition of K+ currents (Fig. 8), strongly suggests that the intrinsic O2 sensor of HEK293 cells is a hemoprotein.
The physiological relevance of the findings reported here is difficult to evaluate because neither the molecular nature of the O2-sensitive K+ channels nor the distribution and coexpression of Kv4.2 with Kvβ1 in native tissues are known. However, our results showing evidence that β subunits provide hypoxic sensitivity to specific KV channel subunits put forth the interesting possibility of the existence of tissue-specific modulatory subunit(s) that confer hypoxic sensitivity to the expressing tissues. This idea is supported by a recent report by Patel et al. (1997) in which a new K channel subunit, Kv9.3, that does not form a channel itself, is able to coassemble with Kv1.2 and increase the probability of the heteromultimeric channels to be modulated by hypoxia. Finally, our findings provide new clues in the search for the molecular mechanisms of O2 sensing in hypoxia-sensitive tissues, raising a completely new set of questions requiring further investigation.
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ACKNOWLEDGMENTS |
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This study was supported by Spanish Dirección General de Investigación Científica y Técnica grant PB97/0400 to C. González.
Submitted: 18 December 1998
Accepted: 31 March 1999
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1C subunit of the human cardiac L-type Ca2+channel, J Physiol, 1997, 500, 551–556.1Csubunits by redox agents and hypoxia, J Physiol, 1999, 514, 629–637.-subunits in mammalian brain K+channel complexes, J Neurosci, 1997, 17, 8246–8258.- and -β complexes of Shaker-like potassium channels, Neuron, 1996, 16, 441–453.[Medline]
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 A. W. Varga, L.-L. Yuan, A. E. Anderson, L. A. Schrader, G.-Y. Wu, J. R. Gatchel, D. Johnston, and J. D. Sweatt Calcium-Calmodulin-Dependent Kinase II Modulates Kv4.2 Channel Expression and Upregulates Neuronal A-Type Potassium Currents J. Neurosci., April 7, 2004; 24(14): 3643 - 3654. [Abstract] [Full Text] [PDF]
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M. Prasad and R. K. Goyal Differential modulation of voltage-dependent K+ currents in colonic smooth muscle by oxidants Am J Physiol Cell Physiol, March 1, 2004; 286(3): C671 - C682. [Abstract] [Full Text]
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 W. Wong and L. C. Schlichter Differential Recruitment of Kv1.4 and Kv4.2 to Lipid Rafts by PSD-95 J. Biol. Chem., January 2, 2004; 279(1): 444 - 452. [Abstract] [Full Text] [PDF]
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S. Y. Lee, P. J. Maniak, D. H. Ingbar, and S. M. O'Grady Adult alveolar epithelial cells express multiple subtypes of voltage-gated K+ channels that are located in apical membrane Am J Physiol Cell Physiol, June 1, 2003; 284(6): C1614 - C1624. [Abstract] [Full Text] [PDF]
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S. M. O'Grady and S. Y. Lee Chloride and potassium channel function in alveolar epithelial cells Am J Physiol Lung Cell Mol Physiol, May 1, 2003; 284(5): L689 - L700. [Abstract] [Full Text] [PDF]
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 L. Conforti, M. Petrovic, D. Mohammad, S. Lee, Q. Ma, S. Barone, and A. H. Filipovich Hypoxia Regulates Expression and Activity of Kv1.3 Channels in T Lymphocytes: A Possible Role in T Cell Proliferation J. Immunol., January 15, 2003; 170(2): 695 - 702. [Abstract] [Full Text] [PDF]
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L. J Teppema, D. Nieuwenhuijs, E. Sarton, R. Romberg, C. N Olievier, D. S Ward, and A. Dahan Antioxidants prevent depression of the acute hypoxic ventilatory response by subanaesthetic halothane in men J. Physiol., November 1, 2002; 544(3): 931 - 938. [Abstract] [Full Text] [PDF]
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I. So and Y. E Earm Is Kv channel inhibition a common path to hypoxic pulmonary vasoconstriction? Cardiovasc Res, August 1, 2002; 55(2): 233 - 235. [Full Text] [PDF]
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D. S Hogg, A. R.L Davies, G. McMurray, and R. Z Kozlowski KV2.1 channels mediate hypoxic inhibition of IKV in native pulmonary arterial smooth muscle cells of the rat Cardiovasc Res, August 1, 2002; 55(2): 349 - 360. [Abstract] [Full Text] [PDF]
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W. Guo, S. A. Malin, D. C. Johns, A. Jeromin, and J. M. Nerbonne Modulation of Kv4-encoded K+ Currents in the Mammalian Myocardium by Neuronal Calcium Sensor-1 J. Biol. Chem., July 12, 2002; 277(29): 26436 - 26443. [Abstract] [Full Text] [PDF]
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 S. Tian, W. Liu, Y. Wu, H. Rafi, A. S. Segal, and G. V. Desir Regulation of the voltage-gated K+ channel KCNA10 by KCNA4B, a novel beta -subunit Am J Physiol Renal Physiol, July 1, 2002; 283(1): F142 - F149. [Abstract] [Full Text] [PDF]
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 W. Muller and K. Bittner Differential Oxidative Modulation of Voltage-Dependent K+ Currents in Rat Hippocampal Neurons J Neurophysiol, June 1, 2002; 87(6): 2990 - 2995. [Abstract] [Full Text] [PDF]
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K. McCormack, J. X. Connor, L. Zhou, L. L. Ho, B. Ganetzky, S.-Y. Chiu, and A. Messing Genetic Analysis of the Mammalian K+ Channel beta Subunit Kvbeta 2 (Kcnab2) J. Biol. Chem., April 5, 2002; 277(15): 13219 - 13228. [Abstract] [Full Text] [PDF]
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W. Guo, H. Li, F. Aimond, D. C. Johns, K. J. Rhodes, J. S. Trimmer, and J. M. Nerbonne Role of Heteromultimers in the Generation of Myocardial Transient Outward K+ Currents Circ. Res., March 22, 2002; 90(5): 586 - 593. [Abstract] [Full Text] [PDF]
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J. X.-J. Yuan Oxygen-sensitive K+ channel(s): where and what? Am J Physiol Lung Cell Mol Physiol, December 1, 2001; 281(6): L1345 - L1349. [Full Text] [PDF]
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E. A. Coppock and M. M. Tamkun Differential expression of KV channel alpha - and beta -subunits in the bovine pulmonary arterial circulation Am J Physiol Lung Cell Mol Physiol, December 1, 2001; 281(6): L1350 - L1360. [Abstract] [Full Text] [PDF]
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G Sanz-Alfayate, A Obeso, M T Agapito, and C Gonzalez Reduced to oxidized glutathione ratios and oxygen sensing in calf and rabbit carotid body chemoreceptor cells J. Physiol., November 15, 2001; 537(1): 209 - 220. [Abstract] [Full Text] [PDF]
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R. Bahring, L. M Boland, A. Varghese, M. Gebauer, and O. Pongs Kinetic analysis of open- and closed-state inactivation transitions in human Kv4.2 A-type potassium channels J. Physiol., August 15, 2001; 535(1): 65 - 81. [Abstract] [Full Text] [PDF]
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 A.J. Patel and E. Honore Molecular physiology of oxygen-sensitive potassium channels Eur. Respir. J., July 1, 2001; 18(1): 221 - 227. [Abstract] [Full Text] [PDF]
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E. A. Coppock, J. R. Martens, and M. M. Tamkun Molecular basis of hypoxia-induced pulmonary vasoconstriction: role of voltage-gated K+ channels Am J Physiol Lung Cell Mol Physiol, July 1, 2001; 281(1): L1 - L12. [Abstract] [Full Text] [PDF]
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 H. L. Reeve, E. Michelakis, D. P. Nelson, E. K. Weir, and S. L. Archer Alterations in a redox oxygen sensing mechanism in chronic hypoxia J Appl Physiol, June 1, 2001; 90(6): 2249 - 2256. [Abstract] [Full Text] [PDF]
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O. Platoshyn, Y. Yu, V. A. Golovina, S. S. McDaniel, S. Krick, L. Li, J.-Y. Wang, Lewis. J. Rubin, and J. X.-J. Yuan Chronic hypoxia decreases KV channel expression and function in pulmonary artery myocytes Am J Physiol Lung Cell Mol Physiol, April 1, 2001; 280(4): L801 - L812. [Abstract] [Full Text] [PDF]
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Y.-X. WANG, P. K. DHULIPALA, and M. I. KOTLIKOFF Hypoxia inhibits the Na+/Ca2+ exchanger in pulmonary artery smooth muscle cells FASEB J, September 1, 2000; 14(12): 1731 - 1740. [Abstract] [Full Text]
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M. T. Perez-Garcia, J. R. Lopez-Lopez, A. M. Riesco, U. C. Hoppe, E. Marban, C. Gonzalez, and D. C. Johns Viral Gene Transfer of Dominant-Negative Kv4 Construct Suppresses an O2-Sensitive K+ Current in Chemoreceptor Cells J. Neurosci., August 1, 2000; 20(15): 5689 - 5695. [Abstract] [Full Text] [PDF]
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N. S. Chandel and P. T. Schumacker Cellular oxygen sensing by mitochondria: old questions, new insight J Appl Physiol, May 1, 2000; 88(5): 1880 - 1889. [Abstract] [Full Text] [PDF]
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L. Conforti, I. Bodi, J. W Nisbet, and D. E Millhorn O2-sensitive K+ channels: role of the Kv1.2 {alpha}-subunit in mediating the hypoxic response J. Physiol., May 1, 2000; 524(3): 783 - 793. [Abstract] [Full Text] [PDF]
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M. T. Perez-Garcia and J. R. Lopez-Lopez Are Kv Channels the Essence of O2 Sensing? Circ. Res., March 17, 2000; 86(5): 490 - 491. [Full Text] [PDF]
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O. N. Osipenko, R. J. Tate, and A. M. Gurney Potential Role for Kv3.1b Channels as Oxygen Sensors Circ. Res., March 17, 2000; 86(5): 534 - 540. [Abstract] [Full Text] [PDF]
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E.-K. Yang, M. R. Alvira, E. S. Levitan, and K. Takimoto Kvbeta Subunits Increase Expression of Kv4.3 Channels by Interacting with Their C Termini J. Biol. Chem., February 9, 2001; 276(7): 4839 - 4844. [Abstract] [Full Text] [PDF]
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S.-Q. Liu, H. Jin, A. Zacarias, S. Srivastava, and A. Bhatnagar Binding of Pyridine Nucleotide Coenzymes to the beta -Subunit of the Voltage-sensitive K+ Channel J. Biol. Chem., April 6, 2001; 276(15): 11812 - 11820. [Abstract] [Full Text] [PDF]
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A. M. Riesco-Fagundo, M. T. Perez-Garcia, C. Gonzalez, and J. R. Lopez-Lopez O2 Modulates Large-Conductance Ca2+-Dependent K+ Channels of Rat Chemoreceptor Cells by a Membrane-Restricted and CO-Sensitive Mechanism Circ. Res., August 31, 2001; 89(5): 430 - 436. [Abstract] [Full Text] [PDF]
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W. Guo, H. Li, F. Aimond, D. C. Johns, K. J. Rhodes, J. S. Trimmer, and J. M. Nerbonne Role of Heteromultimers in the Generation of Myocardial Transient Outward K+ Currents Circ. Res., March 22, 2002; 90(5): 586 - 593. [Abstract] [Full Text] [PDF]
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) or in the presence (•) of Kvβ1.2. Each curve represents the mean ± SEM of 7–20 cells. The insets show representative traces obtained from mock-transfected cells or cells transfected with Shaker or Kv4.2 alone in 20-mV depolarizing steps from –40 to +100 mV. The P values obtained with (M)ANOVA when comparing the I–V curves in the absence and presence of Kvβ1.2 were 0.006 (endogenous currents), 0.084 (Shaker currents), and 0.204 (Kv4.2 currents).
1 and 
70% the effect of low pO2. (B) Averaged values (mean ± SEM) of current inhibition by hypoxia (100% N2, open bar) and CO (20% CO in N2, crosshatched bar) obtained in paired data from 11 cells, and expressed as in Fig.