Base induced hyperpolarization of the cell potential in HCO ⁻₃ free perfused necturus renal proximal tubules

Abstract

Short-term peritubular alkalinization from 7.5 to 8.5 hyperpolarized (−8.8 mV) the basolateral membrane potential (V ₁) in HCO ⁻₃ free Hepes buffered Necturus renal proximal tubule cells. This sustained base induced hyperpolarization (BIH) was associated with an increase in the peritubular apparent transference number for potassium ($t_{K^ + }$). The apparent transference number for potassium ($t_{K^ + }$) was estimated at pH 7.5 and 8.5 by raising peritubular K⁺ from 2.5 to 10 mmol/l.$t_{K^ + }$ increased linearly asV ₁ hyperpolarized, whereas$t_{K^ + }$ measured in the presence of peritubular Ba²⁺ at pH 7.5 and 8.5 was nearly zero. However, the BIH persisted in the presence of barium at the peritubular, luminal or both sides of the epithelium. Moreover this BIH was also accompanied by a small hyperpolarization (−0.4 mV) of the transepithelial membrane potential (V ₃) in the absence or presence of peritubular and/or luminal Ba²⁺. Therefore we conclude that BIH must originate from additional mechanisms other than an increase in peritubular or luminal potassium conductance.