The Journal of General Physiology
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Published online Dec 27 2005. doi:10.1085/jgp.200509384
The Rockefeller University Press, 0022-1295 $8.00
JGP, Volume 127, Number 1, 15-34
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ARTICLE

 Intracellular pH Modulates Taste Receptor Cell Volume and the Phasic Part of the Chorda Tympani Response to Acids

Vijay Lyall1, Hampton Pasley1, Tam-Hao T. Phan1, Shobha Mummalaneni1, Gerard L. Heck1, Anna K. Vinnikova2, and John A. DeSimone1

1 Department of Physiology, Virginia Commonwealth University, Richmond, VA 23298
2 Department of Internal Medicine, Virginia Commonwealth University, Richmond, VA 23298

Correspondence to Vijay Lyall: vlyall{at}hsc.vcu.edu

The relationship between cell volume and the neural response to acidic stimuli was investigated by simultaneous measurements of intracellular pH (pHi) and cell volume in polarized fungiform taste receptor cells (TRCs) using 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF) in vitro and by rat chorda tympani (CT) nerve recordings in vivo. CT responses to HCl and CO2 were recorded in the presence of 1 M mannitol and specific probes for filamentous (F) actin (phalloidin) and monomeric (G) actin (cytochalasin B) under lingual voltage clamp. Acidic stimuli reversibly decrease TRC pHi and cell volume. In isolated TRCs F-actin and G-actin were labeled with rhodamine phalloidin and bovine pancreatic deoxyribonuclease-1 conjugated with Alexa Fluor 488, respectively. A decrease in pHi shifted the equilibrium from F-actin to G-actin. Treatment with phalloidin or cytochalasin B attenuated the magnitude of the pHi-induced decrease in TRC volume. The phasic part of the CT response to HCl or CO2 was significantly decreased by preshrinking TRCs with hypertonic mannitol and lingual application of 1.2 mM phalloidin or 20 µM cytochalasin B with no effect on the tonic part of the CT response. In TRCs first treated with cytochalasin B, the decrease in the magnitude of the phasic response to acidic stimuli was reversed by phalloidin treatment. The pHi-induced decrease in TRC volume induced a flufenamic acid–sensitive nonselective basolateral cation conductance. Channel activity was enhanced at positive lingual clamp voltages. Lingual application of flufenamic acid decreased the magnitude of the phasic part of the CT response to HCl and CO2. Flufenamic acid and hypertonic mannitol were additive in inhibiting the phasic response. We conclude that a decrease in pHi induces TRC shrinkage through its effect on the actin cytoskeleton and activates a flufenamic acid–sensitive basolateral cation conductance that is involved in eliciting the phasic part of the CT response to acidic stimuli.

Abbreviations used in this paper: BAPTA-AM, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis-(acetoxymethyl ester); BCECF, 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein; Bz, benzamil; cAMP, adenosine 3'5'-cyclic monophosphate; CPC, cetylpyridinium chloride; CT, chorda tympani; DAPI, 4',6-diamidino-2-phenylin; F, filamentous; FIR, fluorescence intensity ratio; G, monomeric; NHE-1, Na+-H+-exchanger-1; NPPB, 5-nitro-2-(3-phenylpropylamino)-benzoate; ROI, region of interest; RVD, regulatory volume decrease; RVI, regulatory volume increase; SANSCC, shrinkage-activated nonselective cation channel; TRC, taste receptor cell; TRP, transient receptor potential; VGCC, voltage-gated Ca2+ channel.


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