The communication between nerve cells ultimately depends on release of chemical messengers termed neurotransmitters from one nerve cell and subsequent activation of another nerve cell by the released neurotransmitter. Neurotransmitters are released from a specialized portions of a nerve cell called nerve endings or nerve terminals. The most important initiator of neurotransmitter release at nerve terminals is the concentration of free calcium within the terminal. As a consequence of their small size and of their being mixed with glial cells and other nerve cell regions in intact tissue, direct investigation of the basic secretory mechanisms at nerve endings of vertebrates has been limited. It is the purpose of this proposal to utilize a unique nerve terminal preparations of vertebrates which overcomes the above limitations to characterize the fundamental relationships between calcium and induction of secretion of the chemical messengers. State of the art electrophysiological and optical approaches which provide high quantitative and high time resolution will be used in the proposed studies. Specific questions that will be addressed include: What are the qualities of the changes in intracellular calcium that are most important for initiation of secretion? Which calcium entry pathways are most important for induction of the secretory response? Does continued activation by electrical activity alter the importance of these influx pathways? In addition, a number of specific proteins have recently been implicated in the chain of events leading to secretion by biochemical evidence. To date, the specific functions of these proteins have not been elucidated and is a specific aim of this proposal.
