Ca2+-dependent sensitization of adenylyl cyclase activity

It has been shown that intracellular Ca2+ concentrations have multiple modu latory influences on hormone-stimulated adenylyl cyclase activity. Here, we report that increasing intracellular Ca2+ concentration by treating cells with the Ca2+ ionophore A23187 leads to a sensitization of the beta -adreno ceptor-stimulated adenylyl cyclase activity in Ltk(-) cells expressing the human beta (2)-adrenoceptor. The ionophore treatment led to a 20 +/- 5% inc rease of the maximal isoproterenol-stimulated cyclase activity that could b e prevented by chelation of the extracellular Ca2+ using EGTA. A similar Ca 2+-mediated sensitization (20 +/- 6%) was observed when the adenylyl cyclas e was directly stimulated by the diterpene forskolin indicating that the ca talytic activity of the enzyme itself is modulated by the change in Ca2+ co ncentration. Sensitization of both the isoproterenol- and forskolin-stimula ted adenylyl cyclase activities were completely blocked by treatment with K N-62{1-[ N, O-bis-(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpipe razine}, an inhibitor of the Ca2+-calmodulin-dependent protein kinase (CamK inase). Taken together, our data reveal the existence of a CamKinase-depend ent sensitization process acting at the level of the adenylyl cyclase catal ytic moiety. (C) 2001 Elsevier Science B.V. All rights reserved.