EFFECT OF ACIDOSIS ON CA2-RETICULUM OF INTACT RAT VENTRICULAR MYOCYTES( UPTAKE AND RELEASE BY SARCOPLASMIC)

The effect of acidosis on Ca2+ uptake and release by the sarcoplasmic reticulum (SR) of rat ventricular myocytes has been investigated. Intr acellular Ca2+ concentration ([Ca2+](i)) was monitored using fura 2; t he L-type Ca2+ current (I-Ca) was monitored using the perforated patch -clamp technique. Acidosis was produced either by superfusing the cell s with an acid solution (intracellular and extracellular acidosis) or by NH4Cl withdrawal (intracellular acidosis). Both types of acidosis i ncreased the amplitude, and slowed the declining phase, of the Ca2+ tr ansient. Application of caffeine produced a rise of [Ca2+](i), which d eclined in the continued presence of caffeine; the declining phase was slowed by the acid solution but was unaffected by NH4Cl withdrawal. A cidosis decreased the fraction of the caffeine-induced release that wa s released by electrical stimulation but had no effect on I-Ca. It is concluded that acidosis inhibits SR Ca2+ uptake and Ca2+-induced Ca2release in intact myocytes but that these effects are compensated by a n increase in SR Ca2+ content secondary to a rise in cytoplasmic [Ca2].