Abstract
The release of neurotransmitters at classical chemical synapses occurs via Ca 2+ influx through voltage-dependent Ca 2+ channels, which are opened following depolarization of presynaptic terminals. However, owing to a persistence or increase in the amount of transmitter released in preparations containing low concentrations of Ca 2+, it has been proposed that transmitter release could also occur through a Ca 2+-independent, carrier-mediated process. On the other hand, lowering extracellular [Ca 2+] can actually promote Ca 2+ influx through voltage-activated Ca 2+, channels via a modification of the surface potential of plasma membranes. Therefore, the proposed Ca 2+-independent transmitter release could be re-accommodated within the framework of the Ca 2+ hypothesis of synaptic transmission by taking into account the surface-charge effects.
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