[Exocytosis as the mechanism for neural communication. A view from chromaffin cells]

Exocytosis constitutes the main cellular mechanism for secreting neurotransmitters. It entails the fusion of a secretory vesicle with plasma membrane, thus promoting the release of its soluble content. Among the cell models that have provided insight into molecular machinery underlying the succesive steps of exocytosis, adrenal chromaffin cells have taken a prominent place. Exocytosis gave support to the classical quantal theory, which maintains that neurotransmitters are released as discrete packages from the nerve terminals towards the postsynaptic cell. We present here a brief review of the estate of our knowlegments about the secretory vesicle traffic towards the cell membrane and how exocytosis takes place through the so called SNARE hypothesis. We also review the novel mechanisms implicated in the regulation of the late steps of exocytosis as well as their possible role as target for drug therapy