Alpha 1- and beta-adrenergic and muscarinic-cholinergic regulation in the spontaneous beating and Ca2+ oscillations in cultured neonatal rat cardiac myocytes.

ABSTRACT

alpha 1- and beta-adrenergic and muscarinic-cholinergic regulation in spontaneous beating and Ca2+ oscillations in neonatal rat cardiac myocytes at day 6 of culture was investigated. The spontaneous beating in myocytes decreased in the presence of 10 microM norepinephrine (NE). This 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 beating rate which was antagonized by propranolol. NE increased inositol phosphate formation whereas CCh and ISP did not. NE and CCh suppressed the frequency of the spontaneous Ca2+ oscillations but ISP increased. The present results suggest that alpha 1-adrenergic and muscarinic receptors regulate chronotropism to be negative whereas beta-adrenoceptor regulates chronotropism to be positive in cultured neonatal rat cardiac myocytes.