FM1–43 measurements of local exocytotic events in rat melanotrophs

We have explored the existence of fusion- and secretion-competent sites on the plasma membrane of peptide secreting rat pituitary melanotrophs at rest, and following stimulation with glutamate. We monitored changes in fluorescence of FM1–43, a styryl dye which labels plasma membrane. The results show spontaneous local increases in FM1–43 reporting changes in membrane surface area due to cumulative exocytosis. Addition of glutamate, further increased the occurrence of these events. Statistical analysis of local FM1–43 fluorescence changes suggests that this is due to the recruitment of inactive exocytotic domains and due to the stimulation of already active exocytotic domains.