Calcium-dependent release of neurotransmitters is a crucial step in virtually all aspects of central and peripheral neuron function. Calcium ions are known to enter the nerve terminal via voltage-gated ion channels, but the study of presynaptic calcium channels in vertebrates has been limited by the lack of suitable experimental preparations. We have recently reported the first recording of calcium currents in a vertebrate presynaptic nerve terminal using the calyx synapse of the check ciliary ganglion. This calcium current was shown to have characteristics consistent with a role in synaptic transmission: rapid activation, resistance to dihydropyridine blockers, and sensitivity to block by omega-conotoxin. In a continuation of this study, we have recorded presynaptic calcium currents at the single-channel level and have shown that these channels are located on the release face of the nerve terminal, have a single-channel conductance in the 13pS range, and can be highly clustered. This study is the first description of calcium channel properties at the single-channel level at a presynaptic nerve terminal.
