An Electrophysiological Approach to the Regulation of Neuronal Voltage-Activated Calcium Channels by Guanine Nucleotide Binding Proteins

Neuronal voltage-activated Ca²⁺ channels have received consider- able attention from scientists because of the central role played by Ca²⁺ in the transduction of electrical activity to chemical signals. The importance of neuronal electrical activity resulting in a rise in intra- cellular Ca²⁺ is highlighted at the presynaptic nerve terminal. Depo- larization of the presynaptic nerve terminal results in influx of Ca²⁺ through voltage-activated Ca²⁺ channels. This Ca²⁺ influx contributes to the depolarization, but more importantly, the increase in intra- cellular Ca²⁺ activates biochemical events culminating in vesicular release of neurotransmitter. Electrophysiological studies on presyn- aptic nerve terminals have proved difficult because of access problems and the small size of most terminals. A number of preparations, how- ever, have been amenable to studying presynaptic Ca2+ channel activ- ity. These include:

1.	The squid giant presynaptic terminal (1 );
2.	Peptidergic nerve terminals of the rat neurohypophysis (2 ); and
3.	Frog motor endings (3 ).