BRADYKININ INHIBITS CYCLIC-AMP ACCUMULATION IN D384-HUMAN ASTROCYTOMA-CELLS VIA A CALCIUM-DEPENDENT INHIBITION OF ADENYLYL CYCLASE

Bradykinin causes a concentration-dependent, transient rise in intracellular Ca2+ and a sustained inhibition of forskolin-, dopamine- and 5'-N-ethyl-carboxamidoadenosine (NECA)-stimulated cAMP accumulation in D384 astrocytoma cells. Chelation of intracellular calcium abolished bradykinin's inhibitory effect on cAMP accumulation. Chelating extracellular Ca2+ did not block the initial, but eliminated the sustained inhibition of cAMP accumulation. Increasing Ca2+ influx by calcium ionophore A23187 caused a concentration-dependent inhibition of stimulated cAMP accumulation. A hydroquinone derivative 2,5-di(tert-butyl)-1,4-benzohydroquinone tBuBHQ), which inhibits microsomal C2+ sequestration, did not mimic the effect of bradykinin, although it increased [Ca2+]i even more than A23187 did. The inhibitory effect of bradykinin was not mediated by Ca2+/CaM-dependent stimulation of phosphodiesterase (PDE). Forskolin-stimulated adenylyl cyclase activity was inhibited by Ca2+ (10(-7) to 10(-3) M), both in ethyleneglycol-bis-(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) washed and native D384 plasma membranes. This effect was not altered by calmodulin (CaM) or CaM-antagonists. Bradykinin treatment, which attenuates cAMP accumulation in intact cells, did not do so in plasma membranes. These findings suggest that bradykinin-induced inhibition of cAMP formation in D384 cells requires mobilization of [Ca2+]i and subsequent entry of Ca2+ which directly interacts with a component of the adenylyl cyclase system.