ABSTRACT
Voltage-dependent calcium channels control the influx of calcium, which couples excitation to secretion of transmitter. They are also responsible for calcium action potentials in dendrites and for excitation–contraction coupling in skeletal, cardiac and smooth muscle. The electrophysiological criteria used to distinguish the channels include: The size of the depolarization needed to activate them. High voltage activated (HVA), need a large depolarization, and low voltage activated (LVA) require only a small depolarization. The size of the depolarization needed to activate them. HVA, need a large depolarization, and LVA require only a small depolarization. L-type channels are located in proximal dendrites of pyramidal neurons and contribute to their excitability but are not the pre-synaptic calcium channels involved in neurotransmitter release. Three types of High voltage activated calcium channel are implicated in transmitter release by the ability of selective toxins to block release.
