pH effects on basolateral membrane ion conductances in gallbladder epithelium.

The pH sensitivity of the basolateral membrane voltage of Necturus gallbladder epithelial cells (Vcs) was evaluated with conventional and pH-sensitive intracellular microelectrodes. Elevating solution CO2 from 1 to 5% (at constant [HCO3-] = 10 mM) caused a depolarization of Vcs from -76 +/- 3 to -60 +/- 2 mV and a decrease in intracellular pH (pHi) from 7.36 +/- 0.04 to 7.05 +/- 0.03. Serosal exposure to a 50 mM HCO3(-)-5% CO2 solution [at constant extracellular pH (pHo)] caused a similar cell acidification (delta pHi = 0.27), whereas at 3 min Vcs was unchanged. Exposure to 1 mM HCO3- (at constant CO2) depolarized Vcs from -77 +/- 2 to -56 +/- 2 mV and caused a small decrease in pHi (from 7.36 +/- 0.03 to 7.33 +/- 0.03). These results indicate that the observed depolarizations of Vcs are attributable to changes in pHo and not in pHi. Basolateral membrane potassium conductance (GK) congruent to chloride conductance (GCl) congruent to 0.50 mS/cm2 in 10 mM HCO3(-)-1% CO2 Ringer. The depolarization of Vcs caused by elevation of serosal [K+] in 50 mM HCO3(-)-5% CO2 was similar to that observed under control conditions. In contrast, the depolarization of Vcs elicited by elevating serosal [K+] was reduced by about two-thirds in 1 mM HCO3-, whereas the depolarization caused by reduction of serosal [Cl-] was increased twofold in 1 mM HCO3-, compared with control. Inasmuch as the apparent ratio of membrane resistances remained unchanged during serosal solution acidification, the most likely explanation for the observed decrease in Vcs is a reduction of basolateral K+ permeability concomitant with an increase in Cl- permeability.