Modulation of beta-endorphin secretion from mouse pituitary tumor cells by calmodulin inhibitor W7

The involvement of calmodulin in the secretion of beta-endorphin from the mouse anterior pituitary tumor cell line, AtT-20, was investigated. The calmodulin inhibitor W7 potentiated secretion produced by 8-BrcAMP, and induced a secretory response to arginine vasopressin, which did not elevate beta-endorphin levels when added alone. Release of hormone in response to CRF was not affected. Calmodulin phosphodiesterase inhibitor 8-MeOMeMIX produced a dose-dependent increase in 8-BrcAMP stimulation, suggesting that inhibition of cAMP degradation is the mechanism of enhancement of 8-BrcAMP-induced secretion in the presence of W7.