Effects of acid base disturbances on basolateral membrane potential and intracellular potassium activity in the proximal tubule ofNecturus

Abstract

The effects of extracellular acid-base disturbances on intracellular potential (E _m) and potassium activity (a _K ⁱ ) in the early proximal tubule ofNecturus were examined. Using conventional and double barreled potassium ion selective microelectrodes it was possible to measure both the transient and steady-state responses to various states of extracellular acidosis and alkalosis. The results show that (i) when extracellular [HCO ₃ ⁻ ] is varied at constantpCO₂,E _m anda _K ⁱ decrease in acidosis and increase in alkalosis. The greatest sensitivity inE _m is between pH 7.6 and 6.8 with apparent saturation above and below these extremes; (ii) decreased [HCO ₃ ⁻ ] at constant pH=7.6 also causes a depolarization ofE _m and reducesa _K ⁱ , suggesting a major effect of extracellular [HCO ₃ ⁻ ] on intracellular potential anda _K ⁱ ; (iii) rapid perfusions and transient ΔE _m analysis suggest a high basolateral conductance for K⁺ and HCO ₃ ⁻ and a low Cl⁻ conductance; (iv) increasing extracellular [K⁺] decreases the response of bothE _m anda _K ⁱ to reduced [HCO ₃ ⁻ ] at constantpCO₂. The results of this study demonstrate the important role of extracellular pH and/or [HCO ₃ ⁻ ] on the maintenance of cellular K⁺ homeostasis.