Presynaptic calcium channels: pharmacology and regulation.

Voltage-dependent Ca2+ channels are considered as molecular trigger elements for signal transmission at chemical synapses. Due to their central role in this fundamental process, function and pharmacology of presynaptic Ca2+ channels have recently been the subject of extensive exploration employing various experimental techniques. Several lines of evidence indicate that, at nerve terminals in higher vertebrates, the evoked influx of Ca2+ -ions is mainly mediated by Ca2+ channels of the P-type. The stringent regulation of presynaptic Ca2+ channels is supposed to be involved in fine-tuning the efficiency of synaptic transmission. Intrinsic control mechanisms, such as voltage- or Ca(2+)-dependent inactivation, or modulation of channel activity, either by G-proteins directly or via phosphorylation by protein kinases, may be of particular functional importance.