Increase of calmodulin-stimulated striatal particulate phosphorylation response in chronic haloperidol-treated rats

Calcium- and calmodulin-dependent protein kinase and phosphatase activities were studied in rat striatal particulate preparations. The effect of Ca2+ (0.1-0.5 mM) on phosphorylation was completely abolished in the preparation which had been washed 3 times with a buffer containing ethylene glycol bis-(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA, 1.2 mM). Ca2+-stimulated phosphorylation was restored in a dose-dependent manner after calmodulin (1 microgram) was added to the assays. Ca2+ and calmodulin promoted the phosphate incorporation into two major striatal protein bands with estimated Mr at 52 and 40 kdaltons. The presence of phosphatase in the EGTA-pretreated preparations was negligible. Chronic treatment in rats with haloperidol (1 mg/kg, 20 days) produced a significant decrease in the Ca2+-independent phosphorylation but an increase in the extent of Ca2+ and calmodulin-dependent phosphorylation in the striatum. The chronic haloperidol treatment did not alter the striatal [125I]calmodulin binding curve. In vitro, haloperidol (even at 10(-4) M) had no effect on calmodulin-dependent phosphorylation. Haloperidol (10(-4) M) did not reduce the number but decreased the rate of [125I]calmodulin bindign to the striatal particulates. These data suggest that the link between dopamine receptors and calmodulin-dependent enzyme is dissociated in vitro. On the other hand, the potentiated sensitivity of calmodulin-dependent protein kinase in the chronic haloperidol-treated rats correlated with the supersensitive dopamine receptor responses occurred in these rats. Therefore, calmodulin-dependent protein kinase may biochemically regulate dopamine receptor functions in the striatum in vivo.