Anion channel in basolateral cortical membranes of the rabbit kidney

The presence of chloride conductance in basolateral membranes of proximal tubule is controversial. We measured ³⁶Cl uptake in basolateral membranes loaded with KCl and suspended in a K⁺-free solution to create a positive intravesicular potential difference. Under these conditions, ³⁶Cl uptake was maximal at 1 min, remained stable for at least 10 min and decreased to equilibrium levels by 60-120 min. Collapse of the voltage by valinomycin decreased ³⁶Cl uptake by 46%, indicating the presence of K⁺-gradient-dependent chloride uptake. The chloride channel inhibitor diphenylamine-2-carboxylic acid inhibited ³⁶Cl uptake in a dose-dependent fashion. ³⁶Cl uptake was inhibited equally by unlabeled chloride, iodide and nitrate but not by sulfate or gluconate, indicating that the basolateral anion conductance is relatively selective. ³⁶Cl uptake was pH independent but was calcium dependent. Phosphorylation of basolateral membranes with ATP significantly decreased ³⁶Cl uptake, but the inhibitory effect of ATP was not further altered by exogenous cyclic AMP or the active phorbol ester PMA. These data demonstrate the presence of a relatively selective basolateral anion conductance which is regulated by pH, calcium and ATP.