The positive inotropic effect and the hydrolysis of phosphoinositide induced by endothelin-3 in rabbit ventricular myocardium: inhibition by a selective antagonist of ET(A) receptors, FR139317.
Endothelin-3 (ET-3), an isopeptide of ET, had a concentration-dependent positive inotropic effect (PIE) on rabbit papillary muscle. The maximal inotropic response to ET-3 was 65% of the maximal response to isoproterenol. ET-1 elicited a PIE below 10(-9) M, namely, over a concentration range at which ET-3 did not elicit a PIE. The selective ET(A) antagonist FR139317 effectively antagonized the PIE of ET-3. FR139317 abolished the PIE induced by ET-1 (<10(-9)M) but did not inhibit the PIE induced by high concentrations of ET-1. FR139317 also antagonized the PIE of sarafotoxin S6c. ET-3 caused a time- and concentration-dependent increase in [3H]inositol phosphates (inositol monophosphate, inositol bisphosphate and inositol trisphosphate). FR139317 at 10(-5) M decreased the ET-3-induced increase in inositol phosphates by about 60%, whereas it attenuated the increase in [3H]IP1 induced by ET-1 (3 x 10(-8)M) by only 20%. Thus, in the presence of FR139317, the PIEs of ET-3 and ET-1 were partially dissociated from the PI hydrolysis that was induced by these isopeptides. FR139317 inhibited the specific binding of [125I]ET-1 and of [125I]ET-3, and it was apparent that FR139317 had a high-affinity and a low-affinity site for competing for specific binding with each ligand. These findings indicate that different subtypes of the ET receptor are involved in the induction of the PIEs of ET-3 and ET-1. The PIE of ET-3 may be mediated predominantly by ET(A1) receptors that are susceptible to FR139317 and BQ-123 and partially by ET(B) receptor that are inhibited by RES-701-1. Both ET(A1) and ET(A2) receptors may be responsible for the PIE of ET-1, depending on the concentration in rabbit ventricular myocardium.
Endoh
M
M
Department of Pharmacology, Yamagata University School of Medicine, Japan.
Norota
I
I
Yang
H T
HT
Fujita
S
S
Takanashi
M
M
D000818:Animals; D001381:Azepines / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D065128:Endothelin Receptor Antagonists; D016232:Endothelins / Q000378:metabolism / Q000494:pharmacology*; D006868:Hydrolysis; D007211:Indoles / Q000494:pharmacology*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D010716:Phosphatidylinositols / Q000378:metabolism*; D011817:Rabbits; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin / Q000145:classification; D013268:Stimulation, Chemical; D014757:Viper Venoms / Q000494:pharmacology
D001381:Azepines; D065128:Endothelin Receptor Antagonists; D016232:Endothelins; D007211:Indoles; D010716:Phosphatidylinositols; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin; D014757:Viper Venoms; C057354:sarafotoxins s6; C079574:FR 139317