Multitude of ion channels in the regulation of transmitter release

The presynaptic nerve terminal is of key importance in communication in the nervous system. Its primary role is to release transmitter quanta on the a rrival of an appropriate stimulus. The structural basis of these transmitte r quanta are the synaptic vesicles that fuse with the surface membrane of t he nerve terminal, to release their content of neurotransmitter molecules a nd other vesicular components. We subdivide the control of quantal release into two major classes: the processes that take place before the fusion of the synaptic vesicle with the surface membrane (the pre-fusion control) and the processes that occur after the fusion of the vesicle (the post-fusion control). The pre-fusion control is the main determinant of transmitter rel ease. It is achieved by a wide variety of cellular components, among them t he ion channels. There are reports of several hundred different ion channel molecules at the surface membrane of the nerve terminal, that for convenie nce can be grouped into eight major categories. They are the voltage-depend ent calcium channels, the potassium channels, the calcium-gated potassium c hannels, the sodium channels, the chloride channels, the non-selective chan nels, the ligand gated channels and the stretch-activated channels. There a re several categories of intracellular channels in the mitochondria, endopl asmic reticulum and the synaptic vesicles. We speculate that the vesicle ch annels may be of an importance in the post-fusion control of transmitter re lease.