Effects of adrenaline on glycogenolysis in resting anaerobic frog muscles studied by 31P-NMR

The effects of adrenaline (also called epinephrine) on glycogenolysis in living anaerobic muscles were examined based on time-dependent changes of P-31-NMR spectra of resting frog skeletal muscles with and without iodoacetate treatments. The phosphate-metabolite concentration and the intracellular pH determined from the NMR spectra changed with time, reflecting the advancement of various phosphate metabolic reactions coupled with residual ATPase reactions to keep the ATP concentration constant. The results could be explained semi-qualitatively as the ATP regenerative reactions, creatine kinase reaction and glycogenolysis, advanced with time showing the characteristic two phases. Thus, it was clarified for living muscles that adrenaline activates the phosphorylase step of glycogenolysis, and the adrenaline-activated glycogenolysis is further regulated at the phosphofructokinase step by PCr and also possibly by AMP. Associated with the adrenaline-activated glycogenolysis in the examined muscles, the P-i concentration and the intracellular pH, factors affecting the muscle force, changed significantly, suggesting complicated effects of adrenaline on the muscle contractility.