Effects of Calmodulin on Rat Striatal Adenylate Cyclase Activity (Dopamine, Guanyl Nucleotide, Parkinson's Disease).

This thesis describes our investigation of the effects of calmodulin, a 16,800 dalton calcium-binding protein, on adenylate cyclase activity in rat striatal membranes. Rat striatal adenylate cyclase activity is stimulated by the action of dopamine on specific D-1 receptors. Receptor activation is mediated through a GTP-transducing mechanism to increase the activity of the catalytic moiety of adenylate cyclase. We have studied the interaction between calmodulin and dopamine in the activation of adenylate cyclase. In rat striatal membranes depleted of endogenous calmodulin, adenylate cyclase activity was stimulated by calmodulin in a calcium and dose dependent manner. The apparent K(,a) for calmodulin in the activation of adenylate cyclase was 70 nM, and stimulation was maximal at a free calcium concentration of 10('-7) M. Dopamine-stimulated adenylate cyclase activity was enhanced by the addition of calcium and calmodulin; the apparent K(,a) for dopamine decreased 3-fold from 1.1 (mu)M to 0.35 (mu)M. We have distinguished between calmodulin-stimulated and calmodulin-insensitive components of adenylate cyclase by their differential response to the guanyl nucleotide triphosphates, guanosine triphosphate (GTP) and a non-hydrolyzable analog, guanosine-5'-((beta),(gamma)-imido) triphosphate (GppNHp). Adenylate cyclase activity is regulated in part by the action of a high affinity GTPase activity which inactivates the GTP-stimulated enzyme. We found that calmodulin inhibited a high affinity GTPase activity at concentrations of calcium and calmodulin identical to those that stimulated adenylate cyclase activity. Adenylate cyclase activity in the striatum from rats chronically treated with dopamine receptor antagonists (antipsychotic drugs) exhibited an increased sensitivity to dopamine, calmodulin, and GppNHp as compared to saline treated controls. We conclude that calmodulin and dopamine share a common locus of action, and suggest that calmodulin plays a regulatory role in the dopamine-sensitive adenylate cyclase system in rat striatum.Ph.D.PharmacologyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/161041/1/8612640.pd