Low voltage activated calcium channels: from genes to function.

Cloning of three members of low-voltage-activated (LVA) calcium channel family, predominantly neuronal alpha1G and alpha1I, and ubiquitous alpha1H, enabled to investigate directly their electrophysiological and pharmacological profile as well as their putative subunit composition. All the three channels are half-activated at membrane potential about -40 mV and half-inactivated at about -70 mV. Kinetics of alpha1G and alpha1H channels activation and inactivation are similar and faster than that of alpha1I channel. All the three channels are blocked with high affinity by the organic blocker mibefradil. Another high affinity blocker is kurtoxin. Cloned LVA channels are relatively insensitive to antiepileptics, dihydropyridines and omega-conotoxins. Ni2+ is high affinity blocker of alpha1H channel only. Amiloride inhibits the alpha1H channel. The subunit composition of LVA channel remains unclear. Out of known high-voltage-activated calcium channel subunits, alpha2delta-2 and gamma-5 subunits significantly and systematically modified activation and/or inactivation of the current. In contrast, alpha2delta-1, alpha2delta-3, gamma-2 and gamma-4 subunits failed to modulate the current or had only minor effects.