Effect of acidosis on Ca21 uptake and release by sarcoplasmic reticulum of intact rat ventricular myocytes

Hulme, J. T., and C. H. Orchard. Effect of acidosis on Ca21 uptake and release by sarcoplasmic reticulum of intact rat ventricular myocytes. Am. J. Physiol. 275 (Heart Circ. Physiol. 44): H977–H987, 1998.—The effect of acidosis on Ca21 uptake and release by the sarcoplasmic reticulum (SR) of rat ventricular myocytes has been investigated. Intracellular Ca21 concentration ([Ca]i) was monitored using fura 2; the L-type Ca21 current (ICa) 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 NH4Cl withdrawal (intracellular acidosis). Both types of acidosis increased the amplitude, and slowed the declining phase, of the Ca21 transient. Application of caffeine produced a rise of [Ca]i, which declined in the continued presence of caffeine; the declining phase was slowed by the acid solution but was unaffected by NH4Cl withdrawal. Acidosis decreased the fraction of the caffeineinduced release that was released by electrical stimulation but had no effect on ICa. It is concluded that acidosis inhibits SR Ca21 uptake and Ca21-induced Ca21 release in intact myocytes but that these effects are compensated by an increase in SR Ca21 content secondary to a rise in cytoplasmic [Ca21].