Multiple structural elements contribute to voltage-dependent facilitation of neuronal α1C (CaV1.2) L-type calcium channels

Voltage- and frequency-dependent facilitation of calcium channel activity has been implicated in a number of key physiological processes. Various mechanisms have been proposed to mediate these regulations, including a switch between channel gating modes, voltage-dependent phosphorylation, and a voltage-dependent deinhibition of G-protein block. Studying such modulation on recombinant Ca channels expressed in oocytes, we previously reported that α_1C L-type calcium channel contrast with non-L type Ca channels by its ability to exhibit facilitation by pre-depolarization (Voltage-dependent facilitation of a neuronal α_IC L-type calcium channel, E. Bourinet et al., EMBO Journal, 1994; 13, 5032–5039). To further analyze this effect, we have investigated the molecular determinants which mediate the differences in voltage-dependent facilitation between «facilitable» α_1C and «non facilitable» α_1E calcium channels. We used a series of chimeras which combine the four transmembrane domains of the two channels. Results show that the four domains of α_1C contribute to facilitation, with domain I being most critical. This domain is required but not sufficient alone to generate facilitation. The minimal requirement to observe the effect is the presence of domain I plus one of the three others. We conclude that similarly to activation gating, voltage-dependent facilitation of α_1C is a complex process which involves multiple structural elements were domains I and III play the major role.