Differential Regulation by Calmodulin of Basal, GTP-, and Dopamine-Stimulated Adenylate Cyclase Activities in Bovine Striatum (original) (raw)

1988, Journal of Neurochemistry

The concentration requirements of calmodulin in altering basal, GTP-, and dopamine-stimulated adenylate cyclase activities in an EGTA-washed particulate fraction from bovine striatum were examined. In the bovine striatal particulate fraction, calmodulin activated basal adenylate cyclase activity 3.5-fold, with an ECSO of 110 nM. Calmodulin also potentiated the activation of adenylate cyclase by GTP by decreasing the ECso for GTP from 303 k 56 nM to 60 f 10 nM. Calmodulin did not alter the maximal response to GTP. The EC50 for calmodulin in potentiating the GTP response was only 1 1 nM as compared to 1 10 nM for activation of basal activity. Similarly, calmodulin increased the maximal stimulation of adenylate cyclase by dopamine by 50-60%. The EC5o for calmodulin in eliciting this response was 35 nM. These data demonstrate that calmodulin can both activate basal adenylate cyclase and po-tentiate adenylate cyclase activities that involve the activating GTP-binding protein, N,. Mechanisms that involve potentiation of N,-mediated effects are much more sensitive to calmodulin than is the activation of basal adenylate cyclase activity. Potentiation of GTP-stimulated adenylate cyclase activity by calmodulin was apparent at 3 and 5 mM MgClz, but not at 1 or 10 mM MgC12. These data further support a role for calmodulin in hormonal signalling and suggest that calmodulin can regulate cyclic AMP formation by more than one mechanism. Key Words: Basal ganglia-Guanyl nucleotides-Calcium-Dopamine-Adenylate cyclase. Harrison J. K. et al. Differential regulation by calmodulin of basal, GTP-, and dopamine-stimulated adenylate cyclase activities in bovine striatum. J. Neurochem. 51, 345-352 (1988). A limited number of mammalian tissues display an adenylate cyclase activity that is sensitive to an endogenous Ca2+-binding protein, calmodulin (CaM). These include brain, retina, pancreatic islets, adrenal medulla, kidney, and heart (Manalan and Nee, 1984; MacNeil et al., 1985). The response of adenylate cyclase to CaM in nervous tissue, however, is significantly greater than that in other tissues. Much of the evidence to date suggests that CaM stimulates adenylate cyclase activity by binding directly to the catalytic moiety of the enzyme (Salter et al., 198 1 ; Yeager et al., 1985). Although guanyl nucleotides are not required for stimulation of adenylate cyclase by CaM (Heideman et al., 1982; Seamon and Daly, 1982), CaM can affect the activation of guanyl nucleotidemediated activities of adenylate cyclase (Brostrom et