Changes in [Na⁺]_i, compartmental [Ca²⁺], and NADH with dysfunction after global ischemia in intact hearts

Abstract

We measured the effects of global ischemia and reperfusion on intracellular Na(+), NADH, cytosolic and mitochondrial (subscript mito) Ca(2+), relaxation, metabolism, contractility, and Ca(2+) sensitivity in the intact heart. Langendorff-prepared guinea pig hearts were crystalloid perfused, and the left ventricular (LV) pressure (LVP), first derivative of LVP (LV dP/dt), coronary flow, and O(2) extraction and consumption were measured before, during, and after 30-min global ischemia and 60-min reperfusion. Ca(2+), Na(+), and NADH were measured by luminescence spectrophotometry at the LV free wall using indo 1 and sodium benzofuran isophthalate, respectively, after subtracting changes in tissue autofluorescence (NADH). Mitochondrial Ca(2+) was assessed by quenching cytosolic indo 1 with MnCl(2). Mechanical responses to changes in cytosolic-systolic (subscript sys), diastolic (subscript dia), and mitochondrial Ca(2+) were tested over a range of extracellular [Ca(2+)] before and after ischemia-reperfusion. Both [Ca(2+)](sys) and [Ca(2+)](dia) doubled at 1-min reperfusion but returned to preischemia values within 10 min, whereas [Ca(2+)](mito) was elevated over 60-min reperfusion. Reperfusion dissociated [Ca(2+)](dia) and [Ca(2+)](sys) from contractile function as LVP(sys-dia) and the rise in LV dP/dt (LV dP/dt(max)) were depressed by one-third and the fall in LV dP/dt (LV dP/dt(min)) was depressed by one-half at 30-min reperfusion, whereas LVP(dia) remained markedly elevated. [Ca(2+)](sys-dia) sensitivity at 100% LV dP/dt(max) was not altered after reperfusion, but [Ca(2+)](dia) at 100% LV dP/dt(min) and [Ca(2+)](mito) at 100% LV dP/dt(max) were markedly shifted right on reperfusion (ED(50) +36 and +125 nM [Ca(2+)], respectively) with no change in slope. NADH doubled during ischemia but returned to normal on initial reperfusion. The intracellular [Na(+)] ([Na(+)](i)) increased minimally during ischemia but doubled on reperfusion and remained elevated at 60-min reperfusion. Thus Na(+) and Ca(2+) temporally accumulate during initial reperfusion, and cytosolic Ca(2+) returns toward normal, whereas [Na(+)](i) and [Ca(2+)](mito) remain elevated on later reperfusion. Na(+) loading likely contributes to Ca(2+) overload and contractile dysfunction during reperfusion.