INTRACELLULAR PH REGULATION IN ISOLATED MYOCYTES FROM ADULT-RAT HEART IN HCO3-CONTAINING AND HCO3-FREE MEDIA

1. Using microfluorimetry, intracellular pH, buffering capacity and intracellular pH recovery from intracellular acidosis were determined in isolated adult rat ventricular myocytes, in buffers with and without HCO3-. 2. In nominally HCO3--free media, the intracellular pH was higher than in HCO3--containing media. Buffering capacity at resting intracellular pH and at a pH of about 6.3 was also lower in HCO3--free media. 3. In HCO3--free media, recovery from an acid load after an NH4Cl prepulse was almost completely inhibited by the Na+/H+ antiport activity specific inhibitor ethylisopropyl amiloride. However, in the presence of HCO3-, H+ efflux rate was enhanced, and ethylisopropyl amiloride led to only partial inhibition of H+ efflux. Complete inhibition was achieved only with further addition of the anion-transport inhibitor 4,4'-di-isothiocyanatostilbene-2,2'-disulphonate. 4. Thus, in adult rat ventricular myocytes, recovery from intracellular acidosis in the absence of HCO3- was almost wholly due to Na+/H+ antiport activity. in the more physiological situation with HCO3- present, a third of the recovery from an intracellular acid load was attributed to an additional external Na+-dependent di-isothiocyanatostilbene-disulphonate-sensitive H+ efflux.