Addition of 10-5M l-isoproterenol chloride (I chloride) [5984-95-2] to rat ventricular muscle slice preparations for 10 min increased 32P incorporation into 100,000g particulate and 100,000g supernatant (soluble) fractions but not into homogenates or 1000 and 29,000g particulate fractions prepared from the slices.I also produced a 93% increase in 32P incorporation and a 27% increase in inorganic phosphate in TCA-insoluble protein that was obtained from ventricular slice homogenates.An increase in the incorporation of 32P occurred in the 100,000g particulate and supernatant fractions and the acid-insoluble protein within 2 and 1 min, resp.While the β-adrenergic blocking agent propranolol had no effect by itself on 32P incorporation, it prevented the I-induced incorporation of 32P into the 100,000g particulate and supernatant fractions and the acid-insoluble protein.Removal of I from the bathing medium eliminated the differences in 32P incorporation, indicating that the effects of the catecholamine were reversible.l-Norepinephrine bitartrate [51-40-1] and l-epinephrine bitartrate [51-42-3] at 10-5M caused phosphorylation effects similar to that of I.When the slices were bathed under anoxic conditions, I failed to enhance the incorporation of 32P into proteins of the 100,000g particulate and supernatant fractions or acid-insoluble protein.SDS gel electrophoresis of ventricular slice homogenates revealed that I enhanced the 32P incorporation into several myocardial proteins having mol. weights of 155, 94 (glycogen phosphorylase), 79, 68-77, and 54-59 · 103 and decreased the incorporation into a 30 · 103 dalton protein(s).These results are consistent with the notion that catecholamines may increase the phosphorylation of myocardial proteins in the intact myocardium which in turn may play a role in catecholamine-induced glycogenolysis and augmentation of contractility.