Regulation of [Na+i and [Ca2+]i during Myocardial Ischemia and Reperfusion in a Single-Cell Model
To study the regulation of [Na+]i and [Ca2+]i during metabolic inhibition (MI) by the perfusion of 3.3 mM amytal and 5 μM CCCP, [Na+]i and [Ca2+], were measured simultaneously using guinea pig ventricular myocytes that were dual-loaded with SBFI/M and fluo-3/AM. It was suggested that 1) [Na+]i increased during MI by both the activated Na+ influx via Na+-H+ exchange and the suppressed Na+ extrusion via the Na+-K+ pump, 2) Na+-Ca2+ exchange was inhibited during MI, causing the dissociation between [Na+]i and [Ca2+]i, 3) Na+-Ca2+ exchange could be reactivated by energy repletion, resulting in an increase of [Ca2+]i and 4) cell contracture during MI was related to rigor due to energy depletion, while cell contracture after energy repletion was likely to be related to Ca2+ overload. We also investigated the regulation of [Na+]i, [Ca2+]i, and pHi during simulated ischemia (MI with extracellular acidosis) and reperfusion. Na+-H+ exchange was active during simulated ischemia. After reperfusion, Na+-H+ exchange was activated further as pHi was recovered, resulting in an additional [Na+]i elevation.
KeywordsMetabolic Inhibition Energy Depletion Cell Contracture Intracellular Acidosis Simulated Ischemia
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