Transient activation of cyclic AMP-dependent protein kinase and phosphorylase during the cardiac cycle in the canine myocardium in situ and the effect of propranolol.

The activity ratio of cyclic AMP-dependent protein kinase and glycogen phosphorylase were determined at various stages of the contraction cycle in the canine heart in situ. Both activity ratios vary transiently throughout the contraction-relaxation cycle, the higher values occurring during systole. The rise in the activity ratio of protein kinase was found to coincide with the maximum in the level of cyclic AMP. Propranolol pretreatment prevents the transient in the level of the nucleotide as well as in the activity ratio of the kinase indicating i) a causal relationship between these changes and ii) a neurohumoral, beat-to-beat regulation by catecholamines. Contrary the activity ratio of phosphorylase retains, in the presence of propranolol, its transient changes during the cardiac cycle, probably caused by a Ca2+-mediated activation of phosphorylase kinase during the contraction process.