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In intact sheep gonadotropes, the protein kinase inhibitor, staurosporine, inhibited the stimulatory effect of phorbol 12-myristate 13-acetate (PMA) on luteinizing hormone (LH) secretion. Under the same conditions staurosporine enhanced gonadotrophin-releasing hormone (GnRH)-stimulated LH exocytosis without altering the EC50 of GnRH and without affecting basal LH exocytosis. These results suggest that PKC does not play a major role in mediating acute GnRH-stimulated LH exocytosis. Furthermore, they demonstrate that staurosporine enhances GnRH stimulus-secretion coupling. Both extracellular Ca2(+)-dependent and Ca2(+)-independent components of GnRH-stimulated LH secretion were enhanced by the drug. Staurosporine had no effect on GnRH stimulation of cAMP and inositol phosphate synthesis. In permeabilized cells staurosporine did not enhance Ca2(+)- and cAMP-stimulated LH exocytosis. Based on these results we hypothesize that staurosporine inhibits a protein kinase which is activated by GnRH and which negatively modulates GnRH stimulus-secretion coupling.

Type

Journal article

Journal

FEBS Lett

Publication Date

02/07/1990

Volume

267

Pages

111 - 113

Keywords

Alkaloids, Animals, Cells, Cultured, Cyclic AMP, Exocytosis, Inositol Phosphates, Luteinizing Hormone, Pituitary Gland, Anterior, Pituitary Hormone-Releasing Hormones, Protein Kinase Inhibitors, Sheep, Staurosporine, Tetradecanoylphorbol Acetate