Effects of calmodulin antagonists on hormone release and cyclic AMP levels in GH3 pituitary cells.

In GH3 cells the calmodulin antagonists trifluoperazine and N-(6-aminohexyl)-5-chloro-1-napthalene sulphonamide hydrochloride (W-7) showed a dose-dependent, biphasic effect on the release of growth hormone (GH) and prolactin (PRL). Hormone release was inhibited with 15-30 microM trifluoperazine and with 30-80 microM W-7, while stimulation was observed with 50-100 microM trifluoperazine and with 150 microM W-7. Trifluoperazine (greater than or equal to 30 microM) and W-7 (greater than or equal to 80 microM) increased the concentration of cellular cyclic AMP. Sulphoxides of trifluoperazine and chlorpromazine (less than or equal to 150 microM were without effect on hormone release and cellular cyclic AMP. Hydrolysis of cyclic AMP by GH3 cytosol was reduced after incubation of intact GH3 cells with trifluoperazine (15-60 microM). When trifluoperazine was incubated with cytosol, both the high and low affinity forms of cyclic AMP phosphodiesterase were inhibited competitively with calculated Ki of 4.5 and 56 microM, respectively. Stimulation of cyclic AMP phosphodiesterase caused by endogenous calmodulin was blocked by trifluoperazine. Particulate bound adenylyl cyclase activity was inhibited by trifluoperazine, and this effect was counteracted by endogenous calmodulin.