pH i -Dependent membrane conductance of proximal tubule cells in culture (OK): Differential effects on K+- and Na+-conductive channels

Publisher Website
Google Scholar
Abstract
Confluent monolayers of the established opossum kidney cell line were exposed to NH4Cl pulses (20 mmol/liter) during continuous intracellular measurements of pH, membrane potential (PD m ) and membrane resistance (R′ m) in bicarbonate-free Ringer. The removal of extracellular NH4Cl leads to an intracellular acidification from a control value of 7.33±0.08 to 6.47±0.03 (n=7). This inhibits the absolute K conductance (g K+), reflected by a decrease of K+ transference number from 71±3% (n=28) to 26±6% (n=5), a 2.6±0.2-fold rise ofR′ m, and a depolarization by 24.2±1.5 mV (n=52). In contrast, intracellular acidification during a block ofg K+ by 3 mmol/liter BaCl2 enhances the total membrane conductance, being shown byR′ m decrease to 68±7% of control and cell membrane depolarization by 9.8±2.8 mV (n=17). Conversely, intracellular alkalinization under barium elevatesR′ m and hyperpolarizes PD m . The replacement of extracellular sodium by choline in the presence of BaCl2 significantly hyperpolarizes PD m and increasesR′ m, indicating the presence of a sodium conductance. This conductance is not inhibited by 10−4 mol/liter amiloride (n=7). Patch-clamp studies at the apical membrane (excised inside-out configuration) revealed two Na+-conductive channels with 18.8±1.4 pS (n=10) and 146 pS single-channel conductance. Both channels are inwardly rectifying and highly selective towards Cl−. The low-conductive channel is 4.8 times more permeable for Na+ than for K+. Its open probability rises at depolarizing potentials and is dependent on the pH of the membrane inside (higher at pH 6.5 than at pH 7.8).

This publication has 29 references indexed in Scilit: