Protein kinase C activation by phorbol esters induces chromaffin cell cortical filamentous actin disassembly and increases the initial rate of exocytosis in response to nicotinic receptor stimulation.
Nicotinic stimulation and high K+ depolarization of bovine chromaffin cells cause disassembly of cortical filamentous actin networks. Previous work from our laboratory has demonstrated that disassembly of actin filaments is Ca(2+)-dependent, precedes exocytosis and occurs in cortical areas of low cytoplasmic viscosity which are the sites of exocytosis. It has also been suggested that protein kinase C is involved in catecholamine secretion from chromaffin cells. Therefore, the possibility that protein kinase C activation might be implicated in cortical filamentous actin disassembly was investigated. Here we report that phorbol myristate acetate, a protein kinase C activator, causes cortical filamentous actin disassembly. Short-term phorbol ester treatment does not alter the morphology of chromaffin cells; however, 1 h after phorbol ester exposure an increase in cell flattening and membrane ruffling is observed. Phorbol ester-induced cortical filamentous actin disassembly is inhibited by protein kinase C activity inhibitors, is independent of extracellular Ca2+ and has a slower time course than that induced by either nicotinic receptor stimulation or K(+)-depolarization. Phorbol ester effects are likely to be mediated by activation of protein kinase C and not by any changes in intracellular Ca2+ levels, as indicated by measurements of Ca2+ transients. Pretreatment of chromaffin cells with phorbol myristate acetate increases the initial rate of nicotine-evoked catecholamine release. Nicotine-induced cortical actin filament disassembly and catecholamine secretion are partially (29-40%) inhibited by pretreatment of cells with either calphostin C, staurosporine or sphingosine. The results suggest that protein kinase C may be involved in the reorganization of the cortical actin filament network priming the cells for release by removing a barrier to secretory granule mobility. However, its role in exocytosis is modulatory but not essential.
D000199:Actins / Q000378:metabolism*; D000313:Adrenal Medulla / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D004789:Enzyme Activation; D005089:Exocytosis / Q000187:drug effects*; D007700:Kinetics; D046911:Macromolecular Substances; D008856:Microscopy, Fluorescence; D009281:Naphthalenes; D009538:Nicotine / Q000494:pharmacology*; D009638:Norepinephrine / Q000378:metabolism; D011083:Polycyclic Compounds / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000502:physiology*; D013110:Sphingosine / Q000494:pharmacology; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D000199:Actins; D000470:Alkaloids; D046911:Macromolecular Substances; D009281:Naphthalenes; D011083:Polycyclic Compounds; D011978:Receptors, Nicotinic; D009538:Nicotine; D011493:Protein Kinase C; D019311:Staurosporine; C058819:calphostin C; D013110:Sphingosine; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D009638:Norepinephrine