Myocardial recovery during post-ischemic reperfusion: Optimal concentrations of Na+ and Ca2+ in the reperfusate and protective effects of amiloride added to cardioplegic solution

The effects of Na⁺ and Ca²⁺ concentrations in the reperfusate on post-ischemic myocardial recovery were examined. Also, the myocardial protective effects of amiloride, an inhibitor of the Na⁺/Ca²⁺ and Na⁺/H⁺ exchange systems, added to cardioplegic solutions were assessed, using an isolated working rat heart perfusion system. Global myocardial ischemia was induced by 30-min normothermic cardioplegic arrest, using St. Thomas’ solution. The concentration of Na⁺ in the reperfusate varied, stepwise, from 75 to 145 mM/l, and that of Ca²⁺, from 0.1 to 2.5 mM/l. In this study post-ischemic functional recovery was best at 110 mM/l Na⁺ and 1.2–1.8 mM/l Ca²⁺ in the reperfusate. A significantly greater postischemic functional recovery and a lower creatine kinase release were observed when amiloride was added to the cardioplegic solution. Ca²⁺ overload via Na⁺/Ca²⁺ and Na⁺/H⁺ exchange systems would, thus, appear to be due, at least in part, to post-ischemic reperfusion injury.