Measurement of Phosphodiesterase Activity in the Conduction System and Contractile Muscle of the Rat Heart: Evidence of Regional Difference

Given that information regarding the biochemical regulation of cyclic adenosine monophosphate (cyclic AMP)-mediated signal transduction pathway in the atrioventricular node is limited, we quantitatively measured the phosphodiesterase activity in the conduction system and compared it with that in the contractile myocardium of rats by using the enzymatic fluorometric assay with the histochemical method (n = 4). The phosphodiesterase activities in the atrioventricular node, His bundle, and left ventricular myocardium were 87.9±7.8, 54.5±2.7, and 7.8±0.5 pmol/min/mg as cyclic AMP hydrolyzing speed, respectively (mean±SE). These regional differences imply that cyclic AMP-mediated signal transduction pathway in the conduction system may be more dynamically regulated than in the contractile myocardium.