(S-94) Stowe, D.F., Monday 11:30

INTRODUCTION: The temporal relationship between myoplasmic Ca²⁺ overload and contractile dys-function were examined over 60' of reperfusion after 30' of global ischemia.
METHODS: Guinea pig hearts (n = 8) were isolated and per- fused with Krebs-Ringer's solution at 55 mmHg and 38_C. Isovolumetric LVP and + & -dLVP/dt were recorded with free cytosolic [Ca²⁺] transients measured transmurally at the LV free wall with the fluorescent Ca²⁺ probe indo 1. Data, in nM Ca²⁺, were corrected for changes in auto-fluorescence due to ischemia and reperfusion and non-cytosolic Ca²⁺.
RESULTS: The plots show systolic-diastolic (sys-dia) [Ca²⁺] and sys-dia LVP, as well as dia [Ca²⁺] and dia LVP, over 60' of reperfusion. Before isch-emia values were: dia [Ca²⁺] 120 ±15 nM, dia LVP 2 ±2 mmHg, sys-dia [Ca²⁺] 407 ±49 nM, sys-dia LVP 65 ±2 mmHg. The time during 60' of re-perfusion to attain 50% return of initial sys and dia [Ca²⁺], respectively, was 3 and 4 min; the time to attain 50% return of initial sys and dia LVP was 15 and 20 min, respectively.
DISCUSSION: There is an initial inverse relationship between sys-dia [Ca²⁺] and sys-dia LVP, and between dia [Ca²⁺] and diastolic relaxation at 1' reperfusion, that by 60' reperfusion approaches that of the pre-ischemic relationship. There is an early dissociation between sys-dia [Ca²⁺] and con-tractility, and dia [Ca²⁺] and relaxation that im-proves over time. Partial recovery of contractility and relaxation is slower than the return of sys and dia [Ca²⁺]. This study suggests that Ca²⁺ loading in cardiac myocytes is not wholly responsible for mechanical dysfunction on reperfusion.