Introduction into Ca_v2.1 of the homologous mutation of Ca_v1.2 causing the Timothy syndrome questions the role of V421 in the phenotypic definition of P-type Ca2+ channel

摘要

The Timothy syndrome is a multisystem disorder associated with the mutation of a Gly residue (G402 or G406) in the Ca_v1.2 Ca2+ channel. G406 is localized at the end of the IS6 segment and just before the intracellular I–II loop, which is important for the regulation of channel inactivation and the binding of the Ca_vβ subunit. This Gly residue is conserved in all Ca_v1 and Ca_v2 channels, and the G to R exchange produces a strong decrease of inactivation not only in Ca_v1.2 but also in Ca_v2.3. Here, we show that the mutation into Arg or Glu of the homologous Gly residue in Ca_v2.1 (G363) produces also a slowing of inactivation. However, the G-to-A exchange that decreases the inactivation rate in Ca_v1.2 and Ca_v2.3 increases inactivation in Ca_v2.1. Each mutation affects specifically the gating properties of Ca_v2.1 that remain nevertheless modulated by the co-expressed β subunit as with wild-type channel. The strong decrease of inactivation produced by the G363R or G363E mutations was reminiscent to that previously described for a specific splice variant of Ca_v2.1 that contains a single Val residue inserted in the I–II loop (V421). We unexpectedly found that the V421 insertion does not affect the inactivation rate of Ca_v2.1 and that the effects previously attributed to this insertion, including those on G-protein regulation, can be reproduced by the G363E mutation. Altogether, our results highlight the role of G363 in gating properties, inactivation kinetics, and G-protein regulation of Ca_v2.1 and the lack of effect of V421 insertion on inactivation.