Abstract: | We report, for the epithelialNa+ channel (ENaC) in A6 cells,the modulation by cell pH (pHc)of the transepithelial Na+ current(INa), thecurrent through the individual Na+channel (i), the openNa+ channel density(No), and thekinetic parameters of the relationship betweenINa and theapical Na+ concentration. Thei andNo were evaluatedfrom the Lorentzian INa noise inducedby the apical Na+ channel blocker6-chloro-3,5-diaminopyrazine-2-carboxamide.pHc shifts were induced, understrict and volume-controlled experimental conditions, byapical/basolateral NH4Cl pulses orbasolateral arrest of theNa+/H+exchanger (Na+ removal; block byethylisopropylamiloride) and were measured with the pH-sensitive probe2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Thechanges in pHc were positivelycorrelated to changes inINa and theapically dominated transepithelial conductance. The sole pHc-sensitive parameter underlyingINa wasNo. Only thesaturation value of theINa kinetics wassubject to changes in pHc.pHc-dependent changes inNo may be causedby influencingPo, the ENaC openprobability, or/and the total channel number,NT = No/Po. |