Actin cytoskeleton and exocytosis in rat melanotrophs

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