A small number of open Ca2+ channels trigger transmitter release at a central GABAergic synapse.

To determine the number of open Ca(2+) channels necessary for transmitter release at the inhibitory basket cell-granule cell synapse in rat hippocampus, we combined presynaptic Ca(2+) imaging, recording of postsynaptic currents and modeling. We found that that the opening of three or fewer Ca(2+) channels triggered transmitter release. Furthermore, a small number of Ca(2+) channels were able to evoke release with high temporal precision, despite stochastic Ca(2+) channel opening.