Information is transferred from one neuron to the next at synapses, points of intimate contact, by the release of a chemical neurotransmitter. While it is well established that the entry of calcium through ion channels is a critical step in the release of the transmitter, the mechanism and the modulation of this process remains poorly understood. We have previously demonstrated that the calyx type presynaptic terminal of the chick ciliary ganglion can be used to record single calcium channel activity at a pre-synaptic nerve terminal release face. We have used this preparation to show that single quanta of transmitter can be released during single calcium channel activity. This result is strong evidence that the calcium channel and the transmitter release mechanism are very closely situated, presumably as part of a multimolecular complex. The calyx was also used to demonstrate a regular spacing of individual calcium channels in the transmitter release face using atomic force microscopy. We have also made the first direct recordings of ligand-gated ion channels, activated by ATP, from a presynaptic nerve terminal. These channels may be important in the feedback modulation of transmitter release.
