Dynamics of full fusion during vesicular exocytotic events: release of adrenaline by chromaffin cells.

Vesicular exocytosis is important in the communication between cells in complex organisms. It controls the release of specific chemical or biochemical messengers stored in the emitting cell, which elicit a response upon detection by the target cells. Secretion of a messenger molecule (a neurotransmitter) was measured electrochemically, which allowed the quantification of cellular events and the validation of current physicochemical models. This model led us to formulate predictions about the occurrence and kinetics of vesicular exocytotic events based on the physicochemical meaning of its key parameters. These predictions were tested successfully through a series of experiments on chromaffin cells, involving changes of osmotic conditions, presence of trivalent ions and cholesterol-induced structuring of the cell plasmic membrane.