The Action of Adrenaline in Cardiac Muscle Dissociation between Phosphorylase Activation and Inotropic Response

Abstract Øye, I. The action of adrenaline in cardiac muscle. Dissociation between phosphorylase activation and inotropic response . Acta physiol. scand. 1965. 65 . 251–258. — Isolated, working rat hearts were used in order to study the relationship between phosphorylase activation and inotropic response after adrenaline administration. At the maximum of inotropic response a small but consistent activation of phosphorylase was found (19.2 per cent of the total activity present in the a form, versus 5.0 per cent in the controls). A lag of about 20 sec separated the time of onset of phosphorylase activation from the time of onset of the inotropic response, phosphorylase activation being the later of the two changes and therefore unlikely to play a part in the chain of events leading to increased force of contraction. In the early phase of the inotropic response no activation of phosphorylase was found when the tissue was extracted in glycerol at 30° C. However, an activation of phosphorylase was revealed in these hearts when aqueous extraction at room temperature was carried out. Most likely this finding reflects an activation of phosphorylase b kinase during the early phase of the inotropic response. The results imply that phosphorylase activation and inotropic response might be triggered by the same initial event, in spite of the dissociation, which has been observed between these two adrenergic effects.