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 recombi nant Ca channels expressed in oocytes, we previously reported that a,, 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 ct,, L-type calcium channel, E. Bourinet et al., EMBO Journal, 1991 : 13, 5032-5039). To further analyze this effect, we have investigated the molecular determi nants which mediate the differences in voltage-dependent facilitation between facilitable alpha (IC) and non facilitable alpha (IE) 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 a,, 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 a,, is a complex process which involves multiple structural elements were domains I and III play the major role. (C) 2001 Elsevier Science Ltd. All rights reserved.