ALPHA(1)-ADRENERGIC AND BETA-ADRENERGIC AND MUSCARINIC-CHOLINERGIC REGULATION IN THE SPONTANEOUS BEATING AND CA2+ OSCILLATIONS IN CULTURED NEONATAL RAT CARDIAC MYOCYTES

alpha(1)- and beta-adrenergic and muscarinic-cholinergic regulation in spontaneous beating and Ca2+ oscillations in neonatal rat cardiac myo cytes at day 6 of culture was investigated. The spontaneous beating in myocytes decreased in the presence of 10 mu M norepinephrine (NE). Th is negative chronotropic action was antagonized by prazosin. Carbachol (CCh) also showed negative chronotropic action which was inhibited by atropine. On the other hand, isoproterenol (ISP) increased the beatin g rate which was antagonized by propranolol. NE increased inositol pho sphate formation whereas CCh and ISP did not. NE and CCh suppressed th e frequency of the spontaneous Ca2+ oscillations but ISP increased. Th e present results suggest that alpha(1)-adrenergic and muscarinic rece ptors regulate chronotropism to be negative whereas beta-adrenoceptor regulates chronotropism to be positive in cultured neonatal rat cardia c myocytes.