ACTIVITY OF PHOSPHORYLASE IN TOTAL GLOBAL-ISCHEMIA IN THE RAT-HEART - A P-31 NMR-STUDY

The uptake and subsequent phosphorylation of deoxyglucose into perfused rat hearts were monitored by 31P NMR. The accumulated deoxyglucose 6-phosphate provided an independent method for measuring cytosolic pH in the normoxic and ischemic heart tissue, and a way of studying the activity of phosphorylase during ischemia. The cytosolic pH measured from the 31P NMR resonance position of deoxyglucose 6-phosphate is in good agreement under all conditions studied with that obtained previously from the Pi resonances. This eliminates any possible doubts about the use of Pi for measuring intracellular pH. Deoxyglucose 6-phosphate in vitro inhibits phosphorylase b but not phosphorylase .alpha.. Its inhibitory effect on glycogenolysis during ischemia is monitored by measuring tissue acidosis by NMR. In the initial stages of ischemia phosphorylase activity is not inhibited; after about 5 min approximately 50% of the activity is inhibited. These observations are interpreted in terms of the relative contributions of phosphorylase a and the AMP-dependent phosphorylase b activities during ischemia.