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 Cl-36 uptake in basolateral membranes loaded with KCl and suspended in a K+-free solution to create a positive intravesicular potential difference. Under these conditions, Cl-36 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 Cl-36 uptake by 46%, indicating the presence of K+-gradient-dependent chloride uptake. The chloride channel inhibitor diphenylamine-2-carboxylic acid inhibited Cl-36 uptake in a dose-dependent fashion. Cl-36 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. Cl-36 uptake was pH independent but was calcium dependent. Phosphorylation of basolateral membranes with ATP significantly decreased Cl-36 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.