To investigate the mechanism underlying postischemic cardiac dysfunction (myocardial stunning), contractility and adenine nucleotide metabolism were studied in three groups of isolated perfused rabbit hearts (control, ischemic, and reperfused), whereas Ca2+ uptake by the sarcoplasmic reticulum (SR) was measured in homogenates obtained from them. The hearts were Langendorff-perfused under constant pressure with Krebs-Henseleit solution at 37 degrees C. Global normothermic ischemia was produced by closing the perfusion line. In the reperfused group, after 15 minutes of ischemia, Krebs-Henseleit solution was perfused for 10 minutes. Developed left ventricular pressure (control, 104 +/- 6.3 mm Hg) and left ventricular dP/dt (2,063 +/- 256.6 mm Hg.sec-1) were significantly decreased in reperfused hearts (left ventricular pressure, 78 +/- 5.9 mm Hg; left ventricular dP/dt, 1,339 +/- 216.3 mm Hg.sec-1). Myocardial ATP content (control, 13.6 +/- 0.98 mumol/g dry wt) decreased during ischemia (4.5 +/- 1.23 mumol/g) but was restored to control level on reperfusion (11.8 +/- 0.68 mumol/g). Maximum velocity of Ca2+ uptake by the SR (Vmax) (control, 49.3 +/- 2.54 nmol.min-1 x mg-1) was significantly depressed by ischemia (36.3 +/- 1.94 nmol.min-1 x mg-1) but was restored to the control value after a 10-minute reperfusion (45.3 +/- 0.79 nmol.min-1 x mg-1). Apparent dissociation constant KCa and the Hill coefficient for Ca2+ uptake were not different between control, ischemia, and reperfusion. To test for the possible role of the SR Ca(2+)-release channel in the effect of ischemia and reperfusion, we measured Ca2+ uptake after incubation of homogenates with 610 microM ryanodine.(ABSTRACT TRUNCATED AT 250 WORDS)
Adenine Nucleotides Animals