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

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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.