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

Abstract

The effects of extracellular acid-base disturbances on intracellular potential (Em) and potassium activity (aiK) in the early proximal tubule of Necturus 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 constant pCO2, Em and aiK decrease in acidosis and increase in alkalosis. The greatest sensitivity in Em 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 of Em and reduces aiK, suggesting a major effect of extracellular [HCO-3] on intracellular potential and aiK; (iii) rapid perfusions and transient delta Em analysis suggest a high basolateral conductance for K+ and HCO-3 and a low Cl- conductance; (iv) increasing extracellular [K+] decreases the response of both Em and aiK to reduced [HCO-3] at constant pCO2. The results of this study demonstrate the important role of extracellular pH and/or [HCO-3] on the maintenance of cellular K+ homeostasis.