Multiple structural elements contribute to voltage-dependent facilitation of neuronal alpha(1C) (Ca(V)1.2) L-type calcium channels

Voltage- and frequency-dependent facilitation of calcium channel activity h as been implicated in a number of key physiological processes. Various mech anisms have been proposed to mediate these regulations, including a switch between channel gating modes, voltage-dependent phosphorylation. and a volt age-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 abil ity to exhibit facilitation by pre-depolarization (Voltage-dependent facili tation 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 inv estigated the molecular determi nants which mediate the differences in volt age-dependent facilitation between "facilitable" alpha (IC) and "non facili table" alpha (IE) calcium channels. We used a series of chimeras which comb ine the four transmembrane domains of the two channels. Results show that t he four domains of a,, contribute to facilitation, with domain I being most critical. This domain is required but not sufficient alone to generate fac ilitation. The minimal requirement to observe the effect is the presence of domain I plus one of the three others. We conclude that similarly to activ ation gating, voltage-dependent facilitation of a,, is a complex process wh ich involves multiple structural elements were domains I and III play the m ajor role. (C) 2001 Elsevier Science Ltd. All rights reserved.