CONTRIBUTION OF CYTOSOLIC IONIC AND ENERGETIC MILIEU CHANGE TO ISCHEMIA-INDUCED AND REPERFUSION-INDUCED INJURY IN GUINEA-PIG HEART - FLUOROMETRY AND NUCLEAR-MAGNETIC-RESONANCE STUDIES

The contribution of cytosolic ion and energy milieu changes to ischemi a/reperfusion injury was investigated in isolated guinea-pig hearts an d mitochondria, with fluorometry and P-31 nuclear magnetic resonance ( NMR). The fura-2 Ca2+ signal during ischemia in the guinea-pig Langend orff heart changed triphasically (phases I, II, and III) and rapidly r eturned to the control level after the reperfusion. These triphasic ch anges during ischemia were affected by various agents that affect the cytosolic ion milieu: the combination of asebotoxin-III and dihydrooua bain (which increase intracellular Na+) caused an increase in Ca2+ lev els in the final stage (phase III) with a manifestation of contracture after the reperfusion of the heart. Inhibitors of the H+-Na+ exchange such as 5-(N-ethyl-N-isopropyl)-amiloride (EIPA) produced a significa nt restorative effect on the contractility of the reperfused heart wit h increased proton and decreased Na+ and Ca2+ in the cytosol. The mito chondrial matrix Ca2+ ([Ca2+](m)) preloaded with abnormally high Ca2levels was markedly increased by perfusion with either a physiologic c oncentration of Ca2+ or an acidified perfusate. These [Ca2+](m) increa ses were reduced by the H+-Na+ and H+-K+ exchange inhibitor (EIPA; ome prazole), respectively. These findings will help to explain the Ca par adox at the mitochondria level (i.e., mitochondria for Ca2+ pumping pl ay an essential role in the cellular homeostasis of Ca2+ for the maint enance of cell functions of the heart, acting like a Ca2+ scavenger in the cytosol). Factors that induce Ca2+ overload on mitochondria via s arcolemmal Ca2+ influx and any exchange mechanisms with Na+, K+, Ca2+, and H+ will lead to a loss of contractility, associated with the extr emely reduced level of free energy change predicted from the reduced A TP . PCr/Pi ratio by P-31 NMR.