Changes in high-energy phosphate compounds of isolated rat hearts during Ca2+-free perfusion and reperfusion with Ca2+.

Isolated rat hearts were perfused with a glucose-containing modified Tyrode solution at 37°C, according to Langendorff. After a 15 min stabilization period, the hearts were perfused for 4 min with a Ca²⁺-free medium and subsequently reperfused with Ca²⁺-containing medium. Reperfusion with Ca²⁺ caused irreversible loss of electrical and mechanical activity of the hearts (calcium paradox). After 30 s of reperfusion with Ca²⁺, myocardial creatine phosphate (CP) and ATP levels were decreased by 65% and 45% respectively. In the same period there was an increase in creatine (15%), ADP (85%) and AMP (2800%). Continued reperfusion with Ca²⁺ resulted in a gradual decrease in the tissue concentration of all compounds. The effluent fluid contained large amounts of creatine and AMP, and relatively minor amounts of CP, ATP and ADP. The results show that reperfusion with Ca²⁺-containing medium, after a short Ca²⁺-free period, produces a sudden and severe decline of myocardial high-energy stores, prior to the release of these compounds.