Enhancement of the dense-core vesicle secretory cycle by glucocorticoid differentiation of PC12 cells: Characteristics of rapid exocytosis and endocytosis

The secretory cycle of dense-core vesicles (DCVs) in physiologically stimul ated patch-clamped PC12 cells was analyzed using both amperometry and capac itance measurements. Untreated cells had low or undetectable Ca currents an d sparse secretory responses to short depolarizations. Dexamethasone (5 mu M) treatment for 5-7 d tripled Ca current magnitude and dramatically increa sed quantal secretion in response to depolarization with action potentials. Such cells expressed L-, N-, and P-type Ca channels, and depolarization ev oked rapid catecholamine secretion recorded as amperometric spikes; the ave rage latency was similar to 50 msec. These spikes were much smaller and sho rter than those of primary adrenal chromaffin cells, reflecting the smaller size of DCVs in PC12 cells. Depolarizing pulse trains also elicited a rapi d increase in membrane capacitance corresponding to exocytosis in different iated but not in naive cells. On termination of stimulation, membrane capac itance declined within 20 sec to baseline indicative of rapid endocytosis ( RE). RE did not take place when secretion was stimulated in the presence of Ba or Sr, indicating that RE is Ca-specific. RE was blocked when either an ti-dynamin antibodies or the pleckstrin homology domain of dynamin-1 was lo aded into the cell via the patch pipette. These studies indicate that neuro endocrine differentiation of PC12 cells with glucocorticoids enhances the d evelopment of the excitable membrane and increases the coupling between Ca channels and vesicle release sites, leading to rapid exocytosis and endocyt osis. Slow catecholamine secretion in undifferentiated cells may be caused in part by a lack of localized secretory machinery rather than being an int rinsic property of dense-core vesicles.