P2-purinoceptor activation stimulates phosphoinositide hydrolysis and inhibits accumulation of cAMP in cultured ventricular myocytes.
Extracellular ATP modulates cardiac contraction through P2-purinoceptors on cardiac myocytes. To elucidate the molecular mechanism of this response, we examined the effects of P2-purinoceptor activation on phosphoinositide (PI) hydrolysis and the cAMP system in cultured ventricular myocytes of fetal mice. In a concentration-dependent manner, ATP stimulated accumulations of [3H]inositol monophosphate, bisphosphate, and trisphosphate with the half-maximum effective concentration of approximately 1 microM in the myocytes labeled with [3H]inositol. The order of efficacy of a series of adenyl compounds for stimulation of PI hydrolysis was adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S), ATP greater than ADP, 5'-adenylylimidodiphosphate (APPNP) greater than alpha,beta-methyleneadenosine 5'-triphosphate (APCPP) greater than beta,gamma-methyleneadenosine 5'-triphosphate, AMP greater than adenosine. On the other hand, 100 microM ATP gamma S inhibited isoproterenol-induced accumulation of cAMP by approximately 70% without decreasing the time to maximal cAMP levels, as measured by radioimmunoassay. This response was also concentration dependent, with a half-maximum inhibitory concentration (IC50) of approximately 1 microM. All of the tested ATP, ADP, and ATP analogues inhibited the cAMP system, and the responses to ATP gamma S, APPNP, and APCPP were insensitive to an A1-purinoceptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine. Pertussis toxin attenuated the ATP-induced PI hydrolysis by no more than 25% at 100 ng/ml but completely suppressed the ATP gamma S-induced inhibition of the cAMP system.(ABSTRACT TRUNCATED AT 250 WORDS)
Yamada
M
M
First Department of Internal Medicine, Kobe University School of Medicine, Japan.
Hamamori
Y
Y
Akita
H
H
Yokoyama
M
M
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism; D006352:Heart Ventricles; D006868:Hydrolysis / Q000187:drug effects; D051379:Mice; D009206:Myocardium / Q000378:metabolism*; D037342:Pertussis Toxin; D010703:Phorbol Esters / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism*; D011983:Receptors, Purinergic / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014970:Xanthines / Q000494:pharmacology
D010703:Phorbol Esters; D010716:Phosphatidylinositols; D011983:Receptors, Purinergic; D010566:Virulence Factors, Bordetella; D014970:Xanthines; C022571:adenosine 5'-O-(3-thiotriphosphate); D000255:Adenosine Triphosphate; C051360:1,3-dipropyl-8-cyclopentylxanthine; D000242:Cyclic AMP; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins