CALCIUM-INDEPENDENT SYNAPTIC TRANSMISSION - ARTIFACT OR FACT

The release of neurotransmitters at classical chemical synapses occurs via Ca2+ influx through voltage-dependent Ca2+ channels, which are op ened following depolarization of presynaptic terminals. However, owing to a persistence or increase in the amount of transmitter released in preparations containing low concentrations of Ca2+, it has been propo sed that transmitter release could also occur through a Ca2+-independe nt, carrier-mediated process. On the other hand, lowering extracellula r [Ca2+] can actually promote Ca2+ influx through voltage-activated Ca 2+ channels via a modification of the surface potential of plasma memb ranes. Therefore, the proposed Ca2+-independent transmitter release co uld be re-accommodated within the framework of the Ca2+ hypothesis of synaptic transmission by taking into account the surface-charge effect s.