Electrophysiological study of the antiluminal membrane in the proximal tubule of Necturus: effect of inorganic anions and SCN−

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Abstract
The effects of anionic substitutions on the electrical potential difference (pd) and conductance characteristics of the antiluminal (peritubular) membrane of the proximal tubule of Necturus kidney were studied. The tubular lumina were filled with oil to minimize potential and conductance contributions from luminal membrane and from paracellular shunt pathway. Isosmotic substitutions, [A [anion concentration]]o for [Cl]o, produced the following average changes in membrane pd (mV): F- +1.7, .**GRAPHIC**. +0.1, Br- -4.5, .**GRAPHIC**. -5.2, I- -7.9, .**GRAPHIC**. -12.1, .**GRAPHIC**. -17.8, SCN- -25.3. The amplitude of the depolarization caused by increase in K concentration (K-depolarization) in the peritubular perfusate was increased during perfusion of the tissue with .**GRAPHIC**. (by 78%), SCN- (45%), I- (23%), .**GRAPHIC**. (20%), Br- (16%); it decreased with F- (by 17%). Comparison of membrane pd at peak K-depolarization in the control state (during KCl perfusion) with that obtained in the experimental state (during KA perfusion) was more reliable than determination of bi-ionic potentials as a qualitative estimate of the permeabilities of the various anions (PA) relative to that of chloride (PCl). Study of both peak K-depolarization pd and bi-ionic potentials yielded the following sequence for halide anion permeabilities: PF > PCl > PBr > PI. The peritubular membrane was substantially more permeable to .**GRAPHIC**. and SCN- than to Cl-. The sequence of membrane conductances during anionic substitutions was: Cl- .simeq. .**GRAPHIC**. < Br- .ltoreq. .**GRAPHIC**. < I- .simeq. F- < .**GRAPHIC**. < .**GRAPHIC**. < SCN-. From the changes in pd induced by K-depolarization, the absolute values of pd at peak K-depolarization and from the changes in membrane conductance induced by anionic substitutions, Br-, I-, .**GRAPHIC**. and SCN- all increased PK; and F- increased PNa (though a smaller increase in PK was not excluded).