Influence of ischemic preconditioning on intracellular sodium, pH, and cellular energy status in isolated perfused heart.

The possible relationships between intracellular Na(+) (Na(i)(+)), bioenergetic status and intracellular pH (pH(i)) in the mechanism for ischemic preconditioning were studied using (23)Na and (31)P magnetic resonance spectroscopy in isolated Langendorff perfused rat heart. The ischemic preconditioning (three 5-min ischemic episodes followed by two 5-min and one 10-min period of reperfusion) prior to prolonged ischemia (20 min stop-flow) resulted in a decrease in ischemic acidosis and faster and complete recovery of cardiac function (ventricular developed pressure and heart rate) after 30 min of reperfusion. The response of Na(i) during ischemia in the preconditioned hearts was characterized by an increase in Na(i)(+) at the end of preconditioning and an accelerated decrease during the first few minutes of reperfusion. During post-ischemic reperfusion, bioenergetic parameters (PCr/P(i) and betaATP/P(i) ratios) were partly recovered without any significant difference between control and preconditioned hearts. The reduced acidosis during prolonged ischemia and the accelerated decrease in Na(i)(+) during reperfusion in the preconditioned hearts suggest activation of Na(+)/H(+) exchanger and other ion transport systems during preconditioning, which may protect the heart from intracellular acidosis during prolonged ischemia, and result in better recovery of mechanical function (LVDP and heart rate) during post-ischemic reperfusion.