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Regulation of a Ca2+-sensitive Adenylyl Cyclase in an Excitable Cell

2000; Elsevier BV; Volume: 275; Issue: 51 Linguagem: Inglês

10.1074/jbc.m006606200

1083-351X

Kent A. Fagan, Robert A. Graf, Shawna Tolman, Jerome Schaack, Dermot M.F. Cooper,

Cellular transport and secretion

In nonexcitable cells, we had previously established that Ca 2+ -sensitive adenylyl cyclases, whether expressed endogenously or heterologously, were regulated exclusively by capacitative Ca 2+ entry (Fagan, K. A., Mahey, R. and Cooper, D. M. F. (1996) J. Biol. Chem. 271, 12438–12444; Fagan, K. A., Mons, N., and Cooper, D. M. F. (1998) J. Biol. Chem . 273, 9297–9305). Relatively little is known about how these enzymes are regulated by Ca 2+ in excitable cells, where they predominate. Furthermore, no effort has been made to determine whether the prominent voltage-gated Ca 2+ entry, which typifies excitable cells, overwhelms the effect of any capacitative Ca 2+ entry that may occur. In the present study, we placed the Ca 2+ -stimulable, adenylyl cyclase type VIII in an adenovirus vector to optimize its expression in the pituitary-derived GH 4 C 1 cell line. In these cells, a modest degree of capacitative Ca 2+ entry could be discerned in the face of a dramatic voltage-gated Ca 2+ entry. Nevertheless, both modes of Ca 2+ entry were equally efficacious at stimulating adenylyl cyclase. A striking release of Ca 2+ from intracellular stores, triggered either by ionophore or thyrotrophin-releasing hormone, was incapable of stimulating the adenylyl cyclase. It thus appears as though the intimate colocalization of adenylyl cyclase with capacitative Ca 2+ entry channels is an intrinsic property of these molecules, regardless of whether they are expressed in excitable or nonexcitable cells.