Inhibition of cyclic AMP accumulation by endothelin is pertussis toxin sensitive and calcium independent in isolated adult feline cardiac myocytes.
The aims of this study were to determine whether endothelin-1 (ET-1), a positive inotropic agent, altered the production of cyclic AMP (cAMP) in adult feline cardiac myocytes and to characterize the effect with respect to G-protein-coupling and calcium regulation of adenylyl cyclase. ET-1 inhibited basal and/or stimulated cAMP accumulation in the intact cardiac myocyte and in membrane preparations in a dose-dependent manner. In intact cells, maximal inhibition of forskolin-stimulated cAMP accumulation was 90-95% with an EC50 of 5 x 10(-10) M. Inhibition of isoproterenol-stimulated cAMP was biphasic with maximal inhibition of 70% observed by 10(-11)M; at higher doses inhibition was not consistently observed. The inhibitory response to ET-1 occurred in the absence or presence of isobutylmethylxanthine suggesting that activation of cAMP phosphodiesterases was not the means for reducing cAMP levels. Prior exposure of cardiac myocytes to 100ng/ml pertussis toxin blocked the inhibitory action of ET-1, indicating that this response is mediated through the involvement of a pertussis toxin-sensitive G-protein such as Gi. Studies carried out in the absence of extracellular calcium and under conditions of cell-loading with the intracellular calcium chelator, 1,2-bis-(2-aminophenoxy)-ethane-N,N,N'N'-tetraacetic acid-acetoxymethyl ester (BAPTA/AM), suggest that the mechanism by which ET-1 inhibits cAMP accumulation is not calcium-dependent. Thus, inhibition of cAMP accumulation by ET-1 appears to be mediated through a pertussis toxin sensitive protein rather than by activation of phosphodiesterases or calcium inhibition of cardiac forms of adenylyl cyclase. Though unlikely to play a role in the positive inotropic effect of ET-1, transduction of ET-1 responses through Gi suggests another means for regulation of growth in these adult cardiac myocytes.
Jones
L G
LG
Department of Medicine, Gazes Cardiac Research Institute Medical University of South Carolina, Charleston, 29425 USA.
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D037361:Adenylate Cyclase Toxin; D000262:Adenylyl Cyclases / Q000502:physiology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002316:Cardiotonic Agents / Q000494:pharmacology*; D002415:Cats; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D016232:Endothelins / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000502:physiology; D006321:Heart / Q000187:drug effects*; D007545:Isoproterenol / Q000494:pharmacology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D037342:Pertussis Toxin; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D012680:Sensitivity and Specificity; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
D037361:Adenylate Cyclase Toxin; D000319:Adrenergic beta-Antagonists; D002316:Cardiotonic Agents; D016232:Endothelins; D010726:Phosphodiesterase Inhibitors; D010566:Virulence Factors, Bordetella; D005576:Colforsin; D000242:Cyclic AMP; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D007545:Isoproterenol; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine