Intracellular pH shifts in cultured kidney (A6) cells: effects on apical Na+ transport

Intracellular pH shifts in cultured kidney (A6) cells: effects on apical Na + transport. Am. J. Physiol. 277 (Cell Physiol. 46): C469-C479, 1999.-We re port, for the epithelial Nat channel (ENaC) in A6 cells, the modulation by cell pH (pH(c)) of the transepithelial Na+ current (I-Na), the current thro ugh the individual Na+ channel (i), the open Nat channel density (N-o), and the kinetic parameters of the relationship between INa and the apical Naf concentration. The i and N-o, were evaluated from the Lorentzian IN, noise induced by the apical Na+ channel blocker 6-chloro-3,5-diaminopyrazine-2-ca rboxamide pH(c) shifts were induced, under strict and volume-controlled exp erimental conditions, by apical/basolateral NH4Cl pulses or basolateral arr est of the Na+/H+ exchanger (Nat removal; block by ethylisopropylamiloride) and were measured with the pH-sensitive probe 2',7'-bis(2-carboxyethyl)-5( 6)-carboxy-fluorescein. The changes in pH, were positively correlated to ch anges in IN, and the apically dominated transepithelial conductance. The so le pH(c)-sensitive parameter underlying INa was N-o. Only the saturation va lue of the INa kinetics was subject to changes in pH(c). pH(c)-dependent ch anges in N-o may be caused by influencing P-o, the ENaC open probability, o r/and the total channel number, N-T = N-o/P-o.