Enhanced inhibition of the EDHF phenomenon by a phenyl methoxyalaninyl phosphoramidate derivative of dideoxyadenosine

Abstract

In rabbit arteries endogenous production of cAMP facilitates electrotonic signalling via gap junctions, thus explaining the ability of P-site inhibitors of adenylyl cyclase to attenuate EDHF-type responses. In the present study, we show that a lipophilic phosphoramidate pronucleotide derivative of dideoxyadenosine, 2′,3′-ddA-PMAPh, exhibits enhanced activity as an inhibitor of EDHF-type smooth muscle hyperpolarizations induced by acetylcholine (ACh) compared to the parent nucleoside 2′,3′-ddA, and that the effects of both compounds can be reversed by the cAMP phosphodiesterase inhibitor IBMX. Neither 2′,3′-ddA nor 2′,3′-ddA-PMAPh depress ACh-evoked endothelial hyperpolarization directly. Modifications in the lipophilicity of dideoxyadenosine and its direct intracellular delivery as a mononucleotide may thus enhance the ability to inhibit adenylyl cyclase and depress electrotonic signalling via myoendothelial gap junctions.