The possible relationship between cardiac relaxing substance and cyclic adenosine 3′,5′-monophosphate

Abstract

Concentrations of cyclic adenosine 3′,5′-monophosphate between 10 −8 M and 10 −4 M were completely without effect on the Mg-stimulated actomyosin ATPase (EC 3.6.1.4) activity of fresh and glycerinated canine cardiac myofibrils. All fibrils were known to be capable of responding to soluble cardiac relaxing substance. Cyclic adenosine 3′,5′-monophosphate also failed to alter either the stimulant effect of Ca or the inhibitory effect of cardiac relaxing substance. We conclude from these and supporting observations, (a) that cyclic adenosine 3′,5′-monophosphate is not cardiac relaxing substance, and (b) that a co-factor capable of conferring relaxing activity upon cyclic adenosine 3′,5′-monophosphate probably does not exist.