Loose Coupling Between Ca 2+ Channels and Release Sensors at a Plastic Hippocampal Synapse

Abstract

From Channel to Sensor The coupling between voltage-activated calcium channels and calcium sensors of exocytosis on synaptic vesicles is a key factor that determines the timing and efficiency of transmitter release. It is still largely unclear how tight this coupling is at mature synapses in the central nervous system. Vyleta and Jonas (p. 665 ) found that mossy fiber boutons contain high concentrations of endogenous calcium buffers that normally limit the amount of calcium that reaches the calcium sensor responsible for neurotransmitter release. As a consequence, the calcium signal available to trigger release is small for the initial action potential. However, after high-frequency stimulation, the endogenous calcium buffer binds calcium and is less able to buffer calcium entry, which allows more calcium to reach the calcium sensor, increasing neurotransmitter release and synaptic facilitation.