title: Molecular basis for the cardiovascular activities of amrinone and AR-L57.
abstract: It has been suggested that amrinone and AR-L57 enhance cardiac contractility either by inhibiting phosphodiesterase activity or altering Ca++ homeostasis. Because these novel agents are potentially useful in the management of heart failure, it was of interest to more clearly define their mechanism(s) of action. Amrinone and AR-L57 caused concentration-dependent increases in the contractile states of either perfused guinea-pig hearts or cultured rat cardiomyocytes. To determine whether these actions might result from an increase in sarcolemmal Ca++ movement, the effects of these agents on Ca++ accumulation were studied in a simple system, dog erythrocytes. Both agents promoted erythrocyte Ca++ accumulation in time and concentration-dependent manners, effects that resulted primarily from increased Ca++ entry. However, because these effects were not measurable at inotropic drug concentrations and were apparent only after a 30-min incubation, they did not provide an explanation for the inotropic effects of these agents. Amrinone and AR-L57 inhibited dog heart phosphodiesterase activity (isozyme III) with EC50 values of 23 and 420 microM, respectively; however, only the inotropic responses to amrinone were attenuated by the muscarinic agonist, carbachol, thereby implying a cAMP (cyclic AMP)-dependent mechanism. In cultured ventricular cells, concentrations of amrinone (2 X 10(-4) M) and AR-L57 (3 X 10(-5) M) that caused maximal inotropic responses were associated with the activation of glycogen phosphorylase, but neither drug significantly increased the activation state of cAMP-dependent protein kinase. To further probe the effects of these drugs on intracellular cAMP and Ca++ metabolism, their effects on protein phosphorylation were studied.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000631:Aminopyridines / Q000494:pharmacology*; D000676:Amrinone; D000818:Animals; D002118:Calcium / Q000097:blood; D002217:Carbachol / Q000494:pharmacology; D002316:Cardiotonic Agents / Q000494:pharmacology*; D002415:Cats; D004912:Erythrocytes / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D007093:Imidazoles / Q000494:pharmacology*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000201:enzymology; D010210:Papillary Muscles / Q000187:drug effects; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D006005:Phosphorylases / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013268:Stimulation, Chemical
chemical_list: D000631:Aminopyridines; D002316:Cardiotonic Agents; D007093:Imidazoles; C012633:AR-L 57 CL; D002217:Carbachol; D006005:Phosphorylases; D011494:Protein Kinases; D010727:Phosphoric Diester Hydrolases; D000676:Amrinone; D002118:Calcium