Vol. 281, Issue 3, 1257-1263, 1997

Regulation of [Ca⁺⁺]_i in Human Neuroblastoma (SH-SY5Y) Cells Expressing Recombinant Rat Angiotensin_1A Receptors by Angiotensin II and Carbachol¹

R. L. McDonald, D. J. Roberts, A. C. V. Palmer, S. G. Ball, P. F. T. Vaughan and C. Peers

Institute for Cardiovascular Research, Leeds University, Leeds LS2 9JT, U.K.

The ability of angiotensin II (AII) to regulate [Ca⁺⁺]_i in human neuroblastoma (SH-SY5Y) cells stably expressing recombinant rat AT_1A receptors 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 (-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 removal of Ca⁺⁺_o, both AII and carbachol elicited a second rise of [Ca⁺⁺]_i. Thapsigargin (1 µM) 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 further rise of [Ca⁺⁺]_i, attributable to activation of both nicotinic and muscarinic receptors, because it was reduced (but not abolished) by mecamylamine (1 µM) and was observed when muscarine was used as the agonist. Thus, activation of recombinant AT_1A and muscarinic receptors in SH-SY5Y cells leads to mobilization of Ca⁺⁺ from a common intracellular pool, and stimulates capacitative Ca⁺⁺ influx. Muscarinic (but not AII) receptor occupancy is capable of stimulating an additional Ca⁺⁺ influx pathway.