Calcium currents in a vertebrate presynaptic nerve terminal: the chick ciliary ganglion calyx.

Ca currents (ICa) were recorded from presynaptic nerve terminals in the chick ciliary ganglion. Ciliary neurons are innervated by a single nerve terminal that extends over a wide area of the neuron surface to form a 'calyx'. The neurons were dissociated enzymatically with the calyx intact and the patch clamp technique was used in the whole cell mode to record ion currents. A small inward ICa (peak current 20-80 pA) was recorded that was blocked by external Cd. Only one component of ICa was detected. This was recruited at positive membrane potentials, exhibited no evidence of inactivation during a 25-ms depolarizing pulse, and deactivated rapidly. Thus, the ICa recorded in this vertebrate presynaptic nerve terminal was similar to the high-voltage activated, fast deactivating, current reported in other neurons.