Intracellular pH regulation in isolated myocytes from adult rat heart in HCO-3-containing and HCO-3-free media

Abstract

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.