Dependence of Cell pH and Buffer Capacity on the Extracellular Acid-Base Change in the Skeletal Muscle of Bullfrog

Abstract

Intracellular pH was measured with single- or double-barreled liquid ion-exchanger microelectrodes in the bullfrog sartorius muscle perfused in vitro. A neutral carrier ligand was used for pH sensor of microelectrodes. Average slopes of the single-barreled microelectrodes were -56.4±1.34mV/pH (n=30) and the double-barreled -52.6±1.34 mV/pH (n=65). While changing acid-base parameters of bathing media (pHe from 6.7 to 8.4, P_CO2 from 3.7 to 37mmHg, and HCO₃^- concentrations from 5 to 75mM), paired muscle cell pH (pHi) and membrane potential (EM) values were determined at 23°C. In control conditions (pHe=7.6, HCO₃^-=15mM, P_CO2=11mmHg), pHi and EM (n=20) averaged 6.99±0.04 (S.E.) and -69.2±2.2mV, respectively. A negative correlation was observed between pHiand EM (correlation coefficient r= -0.564, p<0.002). The change in EM per unit pH change was approximately -30mV, indicating that the H⁺ distribution across the cell membrane only incompletely obeys the Donnan rule. The pHi varied more or less with pHe. Namely, changes in pHe and P_CO2 at constant HCO₃^- produced relatively large changes in pHi, but elevation of pHe and P_CO3^- at constant P_CO2 produced relatively minor rise in pHi. The stability of pHi or the size of buffer capacity were proportional to external HCO₃^- concentrations. These data suggested that a transmembrane distribution of buffer pairs depends largely on non-ionic diffusion of CO₂- HCO₃^- buffer system and partly on ion fluxes of HCO₃^- or H⁺.