DEPENDENCE OF THE CA2-INHIBITABLE ADENYLYL-CYCLASE OF C6-2B GLIOMA-CELLS ON CAPACITATIVE CA2+ ENTRY()

The ability of adenylyl cyclases to be regulated by physiological tran sitions in Ca2+ provides a key point for integration of cytosolic Ca2 concentration ([Ca2+](i)) and cAMP signaling, Ca2+-sensitive adenylyl cyclases, whether endogenously or heterologously expressed, require C a2+ entry for their regulation, rather than Ca2+ release from intracel lular stores (Chiono, Ri, Mahey, R., Tate, G., and Cooper, D. M. F. (1 995) J. Biol. Chem. 270, 1149-1155; Fagan, K., Mahey, R., and Cooper, D. M. F. (1996) J. Biol. Chem. 271, 12438-12444). The present study co mpared the regulation by capacitative Ca2+ entry versus ionophore-medi ated Ca2+ entry of an endogenously expressed Ca2+-inhibitable adenylyl cyclase in C6-2B cells, Even in the face of a dramatic [Ca2+](i) rise generated by ionophore, Ca2+ entry via capacitative Ca2+ entry channe ls was solely responsible for the regulation of the adenylyl cyclase, Selective efficacy of BAPTA over equal concentrations of EGTA in blunt ing the regulation of the cyclase by capacitative Ca2+ entry defined t he intimacy between the adenylyl cyclase and the capacitative Ca2+ ent ry sites. This association could not be impaired by disruption of the cytoskeleton by a variety of strategies. These results not only establ ish an intimate spatial relationship between an endogenously expressed Ca2+-inhibitable adenylyl cyclase with capacitative Ca2+ entry sites but also provide a physiological role for capacitative Ca2+ entry othe r than store refilling.