Intracellular pH transients in squid giant axons caused by CO2, NH3, and metabolic inhibitors

Abstract

The intracellular pH (pHi) of squid giant axons has been measured using glass pH microelectrodes. Resting pHj in artificial seawater (ASW) (pH 7.67.8) at 23°C was 7.32 ± 0.02 (7.28 if corrected for liquid junction potential). Exposure of the axon to 5% CO2 at constant external pH caused a sharp decrease in pHi, while the subsequent removal of the gas caused pH, to overshoot its initial value. If the exposure to CO2 was prolonged, two additional effects were noted; (a) during the exposure, the rapid initial fall in pH, was followed by a slow rise, and (b) after the exposure, the overshoot was greatly exaggerated. Application of external NH4CI caused pH, to rise sharply; return to normal ASW caused pH, to return to a value below its initial one. If the exposure to NH4CI was prolonged, two additional effects were noted: (a) during the exposure, the rapid initial rise in pH, was followed by a slow fall, and (b) after the exposure, the undershoot was greatly exaggerated. Exposure to several weak acid metabolic inhibitors caused a fall in pH, whose reversibility depended upon length of exposure. Inverting the electrochemical gradient for H+ with 100 mM K-ASW had no effect on pH, changes resulting from short-term exposure to azide. A mathematical model explains the pH, changes caused by NH4CI on the basis of passive movements of both NH3 and NH4+. The simultaneous passive movements of CO2 and HCO3− cannot explain the results of the CO2 experiments; these data require the postulation of an active proton extrusion and/or sequestration mechanism. © 1976, Rockefeller University Press., All rights reserved.