REGULATION OF [CA-SY5Y) CELLS EXPRESSING RECOMBINANT RAT ANGIOTENSIN(1A) RECEPTORS BY ANGIOTENSIN-II AND CARBACHOL(+](I) IN HUMAN NEUROBLASTOMA (SH)

The ability of angiotensin II (AII) to regulate [Ca++](i) in human neu roblastoma (SH-SY5Y) cells stably expressing recombinant rat AT(1A) re ceptors was investigated using microfluorimetric methods, and compared to responses obtained by stimulation of native muscarinic receptors. Applications of AII or carbachol produced biphasic rises of [Ca++](i), but in Ca++-free solutions (containing 1 mM ethylene glycol-bis (beta -aminoethyl ether)N,N,N,'N'-tetraacetic acid), both agonists produced only transient monophasic rises of [Ca++](i), and second applications were without effect. Application of Ca-o(++), (2.5 mM) to cells after exposure to either agonist produced a Ni2+-sensitive rise of [Ca++](i) in the absence of agonist (''capacitative Ca++ influx''). After remov al of Ca-o(++), both All and carbachol elicited a second rise of [Ca+](o). Thapsigargin (1 mu M) prevented these second rises of [Ca++](i). During capacitative Ca++ influx, application of AII failed to produce a further rise of [Ca++](i). In contrast, carbachol produced a furthe r rise of [Ca++](i), attributable to activation of both nicotinic and muscarinic receptors, because it was reduced (but not abolished) by me camylamine (1 mu M) and was observed when muscarine was used as the ag onist. Thus, activation of recombinant AT(1A) and muscarinic receptors in SH-SY5Y cells leads to mobilization of Ca++ from a common intracel lular pool, and stimulates capacitative Ca++ influx. Muscarinic (but n ot AII) receptor occupancy is capable of stimulating an additional Ca+ influx pathway.