Indexed on: 01 Dec '75Published on: 01 Dec '75Published in: The Journal of Membrane Biology
The effect of foreign anions on transepithelial potential difference and transepithelial input conductance was studied in the isolated perfusedNecturus kidney. Two microelectrodes (recording and current-injecting) were inserted into the lumen of single proximal tubules and the peritubular perfusate was shifted reversibly for 30–60 sec from a physiologic Ringer's solution to a test solution in which chloride was replaced isosmotically by a foreign anion. The permeability sequence, obtained by potential measurements, was: lactate < glutamate < gluconate < pyruvate < benzene sulfonate ≦ acetate ≦ F < propionate <BrO3<formate<ClO3<Cl<ClO4<I≦Br<NO3<SCN. Transepithelial conductance decreased when the tissue was perfused with anions less permeable than chloride but the conductance sequence was different from the permeability sequence. Such discrepancies were more pronounced during perfusion with hyperpolarizing anions; ClO4− and I− (both more permeable than chloride) produced an important decrease in transepithelial conductance, followed by incomplete reversibility when the perfusion was shifted again to chloride Ringer's. The results are best explained by the presence of weak positive fixed charges, governing anion permeation, at the shunt pathway of the proximal tubule. An analysis of the data allows tentative estimates of shape and size of the sites.