Effect sf changes in action potential shape on calcium currents and transmitter release in a calyx-type synapse of the rat auditory brainstem

We studied the relation between the size of presynaptic calcium influx and transmitter release by making simultaneous voltage clamp recordings from pr esynaptic terminals, the calyces of Held and postsynaptic cells, the princi pal cells of the medial nucleus of the trapezoid body, in slices of the rat brainstem. Calyces were voltage clamped with different action potential wa veforms. The amplitude of the excitatory postsynaptic currents depended sup ralinearly on the size of the calcium influx, in the absence of changes in the time-course of the calcium influx. This result is in agreement with the view that at this synapse most vesicles are released by the combined actio n of multiple calcium channels.