Effects of somatostatin and verapamil on growth hormone release and 45Ca fluxes.

Abstract Increasing the extracellular K + concentration to 71 mM causes a phasic release of growth hormone and efflux of 45 Ca from perifused bovine pituitary cells. Verapamil (20 μM) partially inhibits the initial phase of growth hormone release and 45 Ca efflux and completely inhibits the second phase. Somatostatin (1 μg/ml) partially inhibits both phases of growth hormone release but does not modify K + -induced 45 Ca efflux. Incubation of pituitary cells in 71 mM K + increases 45 Ca incorporation; verapamil (20 μM) completely prevents, and somatostatin (1 μg/ml) partially inhibits, the K + -induced increase in 45 Ca incorporation. The results suggest that 71 mM K + increases both calcium entry into the cells and calcium redistribution within them, and that verapamil only inhibits the K + -induced calcium entry. Somatostatin may inhibit calcium entry into tissue stores.