Demonstration of reversible membrane internalization after exocytosis in the rat neurohypophysis

Isolated rat neurohypophysis was stimulated electrically in media containing fluid phase markers such as carboxyfluorescein and choline. After the markers in the extracellular space were washed out, release of the markers trapped in the tissue was evoked by stimulation. Both the uptake and the release of fluid phase markers were not observed in a Mn2+-containing medium. These results provide direct evidence that internalized vesicles have the function to fuse with plasma membrane in response to Ca2+ entry during electrical stimulation.