LOCALIZATION AND CHARACTERIZATION OF THE SUBTYPE(S) OF MUSCARINIC RECEPTOR INVOLVED IN PROSTACYCLIN SYNTHESIS IN RABBIT HEART

The present study was conducted to localize and characterize the subty pe(s) of muscarinic receptor involved in prostacyclin production elici ted by the cholinergic transmitter acetylcholine (ACh) in various cell types in the rabbit heart. ACh increased prostacyclin synthesis, meas ured as 6-keto-prostaglandin(1 alpha) (6-keto-PGF(1 alpha)), in cultur ed coronary endothelial cells and freshly dissociated ventricular myoc ytes in a dose-dependent manner, but not in cultured coronary smooth m uscle cells of rabbit heart. McN-A-343 2-butyny1)-1-trimethylammonium- m-chlorocarbanilate chloride}, a selective M(1) muscarinic ACh recepto r (mAChR) agonist, did not alter 6-keto-PGF(1 alpha) synthesis in thes e cell types. ACh induced 6-keto-PGF(1 alpha) synthesis in coronary en dothelial cells and ventricular myocytes was not altered by a low conc entration (0.01 mu M) of pirenzepine, an M(1) mAChR antagonist, but wa s reduced by a higher concentration (1 mu M). In coronary endothelial cells, ACh-induced 6-keto-PGF(1 alpha) production was reduced by hexah ydro-sila-difendial (HHSiD), an M(3) mAChR antagonist, and in ventricu lar myocytes by both AF-DX 116 -dihydro-6H-pyrido-[2,3-b]-benzodiazepi ne-6-one}], an M(2) receptor antagonist, and HHSiD. The decrease by AC h of isoproterenol-stimulated cAMP accumulation was minimized by AF-DX 116, but not by HHSID or pirenzepine. Pertussis toxin treatment minim ized ACh-induced decrease in isoproterenol-stimulated rise in cAMP, bu t not ACh-induced 6-keto-PGF(1 alpha) synthesis. These data suggest th at ACh stimulates prostacyclin production in coronary endothelial cell s via M(3) mAChR and in ventricular myocytes via M(2) and M(3) mAChR, and may contribute to its cardiprotective effects. Moreover, ACh induc ed decrease in cAMP, but not the increase in 6-keto-PGF(1 alpha) produ ction, is mediated by pertussis toxin-sensitive G(alpha i) proteins in these cells.