Relation between glycolysis and calcium homeostasis in postischemic myocardium

This study examined the hypothesis that glycolysis is required for functional recovery of the myocardium during reperfusion by facilitating restoration of calcium homeostasis. [Ca²⁺]_i was measured in isolated perfused rabbit hearts by using the Ca²⁺ indicator 1,2-bis(2-amino-5-fluorophenoxy)ethane-N,N,N′,N′-tetraacetic acid (5F-BAPTA) and ¹⁹F nuclear magnetic resonance spectroscopy. In nonischemic control hearts, inhibition of glycolysis with iodoacetate did not alter [Ca²⁺]_i. In hearts subjected to 20 minutes of global zero-flow ischemia, [Ca²⁺]_i increased from 260±80 nM before ischemia to 556±44 nM after 15 minutes of ischemia (p<0.05). After reperfusion with 5 mM pyruvate as a carbon substrate, [Ca²⁺]_i increased further in hearts with intact glycolysis to 851±134 nM (p<0.05 versus ischemia) during the first 10 minutes of reperfusion, before returning to preischemic levels. In contrast, inhibition of glycolysis during the reperfusion period resulted in persistent severe calcium overload ([Ca²⁺]_i, 1,380±260 nM after 15 minutes of reperfusion, p<0.02 versus intact glycolysis group). Furthermore, despite the presence of pyruvate and oxygen, inhibition of glycolysis during early reperfusion resulted in greater impairment of functional recovery (rate/pressure product, 3,722±738 mm Hg/min) than did reperfusion with pyruvate and intact glycolysis (rate/pressure product, 9,851±590 mm Hg/min, p<0.01). Inhibition of glycolysis during early reperfusion was also associated with a marked increase in left ventricular end-diastolic pressure during reperfusion (41±5 mm Hg) compared with hearts with intact glycolysis (16±2 mm Hg, p<0.01). The detrimental effects of glycolytic inhibition during early reperfusion were, however, prevented by initial reperfusion with a low calcium solution ([Ca]_o, 0.63 mM for 30 minutes, then 2.50 mM for 30 minutes). In these hearts, the rate/pressure product after 60 minutes of reperfusion was 12,492±1,561 mm Hg/min (p<0.01 versus initial reflow with [Ca]_o of 2.50 mM). These findings indicate that the functional impairment observed in postischemic myocardium is related to cellular Ca²⁺ overload. Glycolysis appears to play an important role in restoration of Ca²⁺ homeostasis and recovery of function of postischemic myocardium.