|
|
|
|
|
|
|
||
The Journal of General Physiology, Vol 99, 435-461, Copyright © 1992 by The Rockefeller University Press
ARTICLES |
D Kikeri, A Sun, ML Zeidel and SC Hebert
Harvard Center for the Study of Kidney Disease, Harvard Medical School.
Fluorescence and electrophysiological methods were used to determine the effects of intracellular pH (pHi) on cellular NH4+/K+ transport pathways in the renal medullary thick ascending limb of Henle (MTAL) from CD1 mice. Studies were performed in suspensions of MTAL tubules (S- MTAL) and in isolated, perfused MTAL segments (IP-MTAL). Steady-state pHi measured using 2,7-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF) averaged 7.42 +/- 0.02 (mean +/- SE) in S-MTAL and 7.26 +/- 0.04 in IP- MTAL. The intrinsic cellular buffering power of MTAL cells was 29.7 +/- 2.4 mM/pHi unit at pHi values between 7.0 and 7.6, but below a pHi of 7.0 the intrinsic buffering power increased linearly to approximately 50 mM/pHi unit at pHi 6.5. In IP-MTAL, NH4+ entered cells across apical membranes via both Ba(2+)-sensitive pathway and furosemide-sensitive Na+:K+(NH4+):2Cl- cotransport mechanisms. The K0.5 and maximal rate for combined apical entry were 0.5 mM and 83.3 mM/min, respectively. The apical Ba(2+)-sensitive cell conductance in IP-MTAL (Gc), which reflects the apical K+ conductance, was sensitive to pHi over a pHi range of 6.0-7.4 with an apparent K0.5 at pHi approximately 6.7. The rate of cellular NH4+ influx in IP-MTAL due to the apical Ba(2+)- sensitive NH4+ transport pathway was sensitive to reduction in cytosolic pH whether pHi was changed by acidifying the basolateral medium or by inhibition of the apical Na+:H+ exchanger with amiloride at a constant pHo of 7.4. The pHi sensitivities of Gc and apical, Ba(2+)-sensitive NH4+ influx in IP-MTAL were virtually identical. The pHi sensitivity of the Ba(2+)-sensitive NH4+ influx in S-MTAL when exposed to (apical+basolateral) NH4Cl was greater than that observed in IP-MTAL where NH4Cl was added only to apical membranes, suggesting an additional effect of intracellular NH4+/NH3 on NH4+ influx. NH4+ entry via apical Na+:K+ (NH4+):2Cl- cotransport in IP-MTAL was somewhat more sensitive to reductions in pHi than the Ba(2+)-sensitive NH4+ influx pathway; NH4+ entry decreased by 52.9 +/- 13.4% on reducing pHi from 7.31 +/- 0.17 to 6.82 +/- 0.14. These results suggest that pHi may provide a negative feedback signal for regulating the rate of apical NH4+ entry, and hence transcellular NH4+ transport, in the MTAL. A model incorporating these results is proposed which illustrates the role of both pHi and basolateral/intracellular NH4+/NH3 in regulating the rate of transcellular N H4+ transport in the MTAL.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Facebook 
Reddit 
Technorati 
Twitter What's this?
This article has been cited by other articles:
|
|
 |
|
  H.-W. Lee, J. W. Verlander, J. M. Bishop, P. Igarashi, M. E. Handlogten, and I. D. Weiner Collecting duct-specific Rh C glycoprotein deletion alters basal and acidosis-stimulated renal ammonia excretion Am J Physiol Renal Physiol, June 1, 2009; 296(6): F1364 - F1375. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Attmane-Elakeb, H. Amlal, and M. Bichara Ammonium carriers in medullary thick ascending limb Am J Physiol Renal Physiol, January 1, 2001; 280(1): F1 - F9. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. P. Lavelle, S. A. Meyers, W. G. Ruiz, C. A. T. Buffington, M. L. Zeidel, and G. Apodaca Urothelial pathophysiological changes in feline interstitial cystitis: a human model Am J Physiol Renal Physiol, April 1, 2000; 278(4): F540 - F553. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
F. Leviel, D. Eladari, A. Blanchard, J.-S. Poumarat, M. Paillard, and R.-A. Podevin Pathways for HCO-3 exit across the basolateral membrane in rat thick limbs Am J Physiol Renal Physiol, June 1, 1999; 276(6): F847 - F856. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. A. Laamarti, P. D. Bell, and J.-Y. Lapointe Transport and regulatory properties of the apical Na-K-2Cl cotransporter of macula densa cells Am J Physiol Renal Physiol, November 1, 1998; 275(5): F703 - F709. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. Krarup, L. D. Jakobsen, B. S. Jensen, and E. K. Hoffmann Na+-K+-2Cl- cotransport in Ehrlich cells: regulation by protein phosphatases and kinases Am J Physiol Cell Physiol, July 1, 1998; 275(1): C239 - C250. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. N. Nagaraja and N. Brookes Intracellular acidification induced by passive and active transport of ammonium ions in astrocytes Am J Physiol Cell Physiol, April 1, 1998; 274(4): C883 - C891. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Rivers, A. Blanchard, D. Eladari, F. Leviel, M. Paillard, R.-A. Podevin, and M. L. Zeidel Water and solute permeabilities of medullary thick ascending limb apical and basolateral membranes Am J Physiol Renal Physiol, March 1, 1998; 274(3): F453 - F462. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. M. Sun Expression of Cl-/HCO−3 exchanger in the basolateral membrane of mouse medullary thick ascending limb Am J Physiol Renal Physiol, February 1, 1998; 274(2): F358 - F364. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. P. Lavelle, G. Apodaca, S. A. Meyers, W. G. Ruiz, and M. L. Zeidel Disruption of guinea pig urinary bladder permeability barrier in noninfectious cystitis Am J Physiol Renal Physiol, January 1, 1998; 274(1): F205 - F214. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. A. Laamarti and J.-Y. Lapointe Determination of NH+4/NH3 fluxes across apical membrane of macula densa cells: a quantitative analysis Am J Physiol Renal Physiol, November 1, 1997; 273(5): F817 - F824. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. Attmane-Elakeb, H. Boulanger, C. Vernimmen, and M. Bichara Apical Location and Inhibition by Arginine Vasopressin of K+/H+ Antiport of the Medullary Thick Ascending Limb of Rat Kidney J. Biol. Chem., October 10, 1997; 272(41): 25668 - 25677. [Abstract] [Full Text] [PDF]
|
|
|
|
