Biionic potentials in the proximal tubule of Necturus kidney.

1. Biionic potentials were studied in the proximal tubule of the doubly perfused Necturus kidney and subsequently analysed by means of an equivalent electrical circuit.2. Luminal membrane resistance was found to be at least 3 times greater than peritubular membrane resistance.3. Potassium contribution to peritubular membrane conductance amounts to at least 75%. Replacement of chloride in peritubular circulation by benzene sulphonate or acetyl glycinate hyperpolarized peritubular membrane.4. The peritubular membrane is more permeable to choline than to sodium. Indirect evidence suggests that the opposite may apply at the luminal border.5. The shunt pathway discriminates poorly, if at all, between sodium, potassium and choline, in short term experiments.6. Chloride permeability across the shunt pathway is about three times as great as combined cationic permeabilities.