Mechanism of anion permeation in the basolateral membrane of isolated rabbit renal proximal tubule S3 segment

Conventional and double-barreled microelectrodes were used to examine the anion selectivity of Cl- conductance in the basolateral membrane of rabbit renal proximal tubule S3 segment. The permeability sequence determined by anion replacements in the presence of K+ channel blocker quinine was SCN- > I- > Br- > Cl- > gluconate in both nonperfused and luminally perfused tubules. The anion-selective microelectrodes with higher sensitivity to I- enabled us to measure intracellular I- activities. With these electrodes, we could compare the conductive movements of Cl- and I- in response to the increase in bath K+ concentrations and confirmed that the conductance sequence was also I- > Cl-. Although the basolateral potential changes generated by Cl- and Br- currents were stimulated by adenosine 3',5'-cyclic monophosphate (cAMP), the potential changes by SCN- and I- currents were somewhat inhibited by cAMP. In addition, the conductive uptake of I- was, in contrast to that of Cl-, inhibited by cAMP These results are consistent with the existence of at least two distinct anion conductances in this membrane, which are differently regulated by cAMP.