Characterization of Luminal and Peritubular Membrane K+ Selectivity in Proximal Tubular Cells of Frog Kidney

Abstract

The functional significance of KCNQ1/KCNE1 K(+) secretory fluxes and the effects of 3 micromol/L Cd(2+) on the peritubular cell membrane potential and its potassium selectivity were investigated in proximal tubular cells of the frog kidney. Perfusing the lumen with l-phenylalanine plus/minus chromanol 293B, a specific blocker of KCNQ1, did not modify rapid depolarization and rate of slow repolarization of the peritubular cell membrane. Peritubular exposure to Cd(2+) led to a sustained, reversible hyperpolarization of the peritubular membrane, paralleled by an increase in fractional K(+) conductance. Peritubular barium blunted hyperpolarization of the peritubular cell membrane to Cd(2+). Thus, the KCNQ1/KCNE1 K(+) secretory fluxes are absent in proximal tubule of frog kidney, while Cd(2+) increases K(+) selectivity of the peritubular cell membrane.