Brefeldin A Increases the Quantal Size and Alters the Kinetics of Catecholamine Release from Rat Adrenal Chromaffin Cells

The fungal metabolite, brefeldin A (BFA), is known to inhibit guanine nucleotide exchange on the ADP-ribosylating factors that are involved in vesicle membrane trafficking. Here, we investigated the action of BFA on Ca 2+ -regulated exocytosis in single rat adrenal chromaffin cells. Incubation of chromaffin cells with BFA (1 or 10 μ m ) for 2 h effectively disrupted the Golgi membranes but did not affect the pattern of catecholamine release triggered by high extracellular K + , which was monitored with carbon fiber amperometry along with cytosolic Ca 2+ measurement. The BFA treatment, however, increased the mean quantal size of catecholamine-containing vesicles and the occurrence of amperometric events with a “foot” or “stand alone” signal (which reflects sluggish or incomplete dilation of the fusion pore). To examine whether BFA altered the Ca 2+ -dependence of exocytosis, we employed the whole-cell recording technique in conjunction with the capacitance measurement to measure exocytosis evoked from the entire cell during voltage-gated Ca 2+ entry. Our results suggested that BFA treatment did not alter either the initial rate of capacitance increase or the total amount of capacitance increase. Therefore, in chromaffin cells, BFA treatment affects Ca 2+ -regulated exocytosis predominantly by increasing the quantal size and by slowing the fusion kinetics of some vesicles.