Abstract
AbstractIn isolated rat diaphragm suspended in a buffer solution where Na+ had been exchanged for K+ or choline the basal phosphorylaseaactivity was reduced and the phosphorylaseaactivating effect of adrenaline and isoprenaline was blocked or reduced. The total phosphorylase activity and the level of high energy phosphate compounds were unchanged in high‐K+ buffer but the former reduced in choline buffer. The basal phosphorylaseaactivity was reduced in a Ca++‐free solution but the effect of adrenaline was unchanged. The phosphorylaseaactivating effect of the catecholamines is mediated by adenosine 3′,5′‐monophosphate (cyclic AMP). Addition of cyclic AMP to the buffer solution had a stimulating effect on the phosphorylaseaactivity of the rat diaphragm. This effect was blocked or reduced when Na+ in the buffer solution was exchanged for K+ or choline. It has been demonstrated that the stimulating effect of adrenaline on the cyclic AMP content in the diaphragm is unchanged in high‐K+ media. We suggest that the blockade of the phosphorylaseaactivating effect of the catecholamines in high‐K+ media was due to an inhibition of the action of cyclic AMP.
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