Intracellular Calcium Regulation in Cardiac Cells during Acidosis
The effects of intracellular acidosis on Ca2+ regulation mechanism in enzymatically isolated guinea pig ventricular myocytes were studied. Comparable degrees of acidosis were obtained by NH4Cl removal or application of lactate. Intracellular pH and [Ca2+] were monitored using the fluorescent indicators 2′-7′-bis-(carboxyethyl)-5(6)-carboxyfluorescein (BCECF) and indo-1. Release of Ca2+ from the sarcoplasmic reticulum was produced by rapid cooling or application of caffeine. Using caffeine, we have shown that acidosis affects Na+-Ca2+ exchange-mediated Ca2+ extrusion. This effect was not observed when the increase of intracellular Na+ during acidosis was prevented by blocking the Na+-H+ exchange. Using Na+-free/Ca2+-free solution to study the activity of the SR Ca2+ ATPase on cytoplasmic Ca2+, Ca2+ extrusion was slower in the presence of lactate but was unchanged after removal of NH4Cl. Using paired rapid cooling contractures, the relative contributions of the cellular mechanisms to Ca2+ extrusion were investigated. In acidosis produced by application of lactate and acetate, the relative role of the SR Ca2+ uptake was reduced, probably in favor of Na+-Ca2+ exchange.
KeywordsSarcoplasmic Reticulum Ventricular Myocytes Intracellular Acidosis Normal Tyrode Normal Tyrode Solution
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