STAUROSPORINE-INDUCED REDUCTION OF SECRETORY FUNCTION IN CULTURED BOVINE ADRENAL CHROMAFFIN CELLS

Staurosporine, a potent inhibitor of protein kinases, has been used to investigate the involvement of protein kinases in cellular processes such as secretory function and differentiation. We have been examining the effects of staurosporine on secretory function under the same conditions it induces dramatic changes in cell morphology in cultured bovine adrenal chromaffin cells. Our results show that treatment with 100 nM staurosporine reduces catecholamine release stimulated by 56 mM KCl, 10 mu M nicotine, and 2 mM BaCl2 in a time-dependent manner (t(1/2)s, 42, 32, and 31 min, respectively). However, we demonstrate that the time-dependent effects on secretory function are not the direct result of staurosporine-induced changes in cell morphology. The effects of staurosporine on secretion stimulated by KCl, nicotine, and BaCl2 are concentration-dependent (IC(50)s, 6.3, 29.3, and 34.9 nM, respectively). Staurosporine pretreatment does not inhibit activated Ca-45(2+) influx, but does reduce catecholamine release stimulated directly by Ca2+ from permeabilized cells. Furthermore, staurosporine also inhibits basal release with time- and concentration-dependencies (IC50, 9.3 nM and t(1/2), 21 min) similar to those found for stimulated release. These results suggest that prolonged staurosporine pretreatment may result in the depletion/ alteration of a component essential for the more terminal steps of the secretory process.