Calcium-dependent transmitter release from presynaptic nerve terminals is involved in virtually all functions of neurons. We have used the cholinergic calyx-type synapse of the chick ciliary ganglion to develop a unique experimental preparation in which it is possible to apply voltage clamp techniques to the presynaptic nerve terminal. We have used this technique to characterize presynaptic calcium channels by recording the voltage-dependent calcium current. The presynaptic calcium channels are dihydropyridine blocker-insensitive, omega-conotoxin-sensitive but voltage-dependent inactivation resistant. These channels may represent a type that is unique to fast transmitting nerve terminals.
