Effect of acidosis on Ca2+ uptake and release by sarcoplasmic reticulum of intact rat ventricular myocytes

Department of Physiology, University of Leeds, Leeds LS2 9JT, United Kingdom The effect of acidosis on Ca 2+ uptake and release by the sarcoplasmic reticulum (SR) of rat ventricular myocytes has been investigated. Intracellular Ca 2+ concentration ([Ca 2+ ] i ) was monitored using fura 2; the L-type Ca 2+ current ( I Ca ) was monitored using the perforated patch-clamp technique. Acidosis was produced either by superfusing the cells with an acid solution (intracellular and extracellular acidosis) or by NH 4 Cl withdrawal (intracellular acidosis). Both types of acidosis increased the amplitude, and slowed the declining phase, of the Ca 2+ transient. Application of caffeine produced a rise of [Ca 2+ ] i , which declined in the continued presence of caffeine; the declining phase was slowed by the acid solution but was unaffected by NH 4 Cl withdrawal. Acidosis decreased the fraction of the caffeine-induced release that was released by electrical stimulation but had no effect on I Ca . It is concluded that acidosis inhibits SR Ca 2+ uptake and Ca 2+ -induced Ca 2+ release in intact myocytes but that these effects are compensated by an increase in SR Ca 2+ content secondary to a rise in cytoplasmic [Ca 2+ ]. calcium ion; pH; cardiac muscle