Actin cytoskeleton and exocytosis in rat melanotrophs

We monitored secretory activity of single rat melanotrophs by the patch-cla mp membrane capacitance measurements (C-m). Secretory activity was stimulat ed by cytosol dialysis with a patch-pipette solution containing 1 mu M [Ca2 +](i). Actin cytoskeleton was disaggregated by pretreating cells with Clost ridium spiroforme toxin, which specifically ADP-ribosylates cellular actin. The extent of cytoskeleton disaggregation was monitored by phalloidin immu nostaining. The maximal rate of secretion increases two folds in toxin-trea ted cells in comparison to controls, whereas the extent of calcium-induced secretory response was similar to that obtained in the non-treated cells. T he results show that the subcortical actin network attenuates the rate of s ecretory activity, which we interpret to reflect a barrier function of cyto skeleton for exocytosis.