Cyclic ADP-ribose (
cADPR) is a novel Ca(2+)-mobilizing second messenger in mammalian cells including cardiomyocytes. It is unknown whether
myocardial ischemia and reperfusion affect the metabolism of
cADPR in the myocardium. The present study therefore examined the effects of
myocardial ischemia and reperfusion on the concentrations of myocardial
cADPR using high-performance liquid chromatography. Basal levels of
cADPR in rat myocardium were 5.3 +/- 1.8 nmol x mg(-1)
protein.
Myocardial ischemia for 30 min significantly decreased
cADPR concentrations to 2.1 +/- 0.4 nmol x mg(-1)
protein. During reperfusion,
cADPR was maintained at ischemic levels. The activity of
ADP-ribosyl cyclase was expressed as the conversion rate of
nicotinamide guanine dinucleotide (NGD(+)) to
cyclic GDP-ribose.
Myocardial ischemia and reperfusion did not alter the activity of
ADP-ribosyl cyclase. However,
cADPR hydrolase activity, as measured by the conversion rate of
cADPR to
ADP-ribose, was significantly elevated by
ischemia and reperfusion. To determine the mechanism resulting in the enhancement of
cADPR hydrolase activity, we examined the effects of changes in
ADP,
ATP, pH, and PO(2) on the conversion rate of
cADPR to ADPR. Alterations of
ADP,
ATP, or pH in myocardial tissue had no effect on the degradation of
cADPR, whereas a decrease in tissue PO(2) markedly increased the hydrolysis of
cADPR. These results suggest that
myocardial ischemia and reperfusion decrease
cADPR in the myocardium by increasing its hydrolysis. Tissue
hypoxia may be one of the important mechanisms to activate
cADPR hydrolase.