The Timothy syndrome is a multisystem disorder associated with the mutation of a 
Gly residue (G402 or G406) in the Ca(v)1.2 Ca(2+) 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(v)beta subunit. This Gly residue is conserved in all Ca(v)1 and Ca(v)2 
channels, and the G to R exchange produces a strong decrease of inactivation not 
only in Ca(v)1.2 but also in Ca(v)2.3. Here, we show that the mutation into Arg 
or Glu of the homologous Gly residue in Ca(v)2.1 (G363) produces also a slowing 
of inactivation. However, the G-to-A exchange that decreases the inactivation 
rate in Ca(v)1.2 and Ca(v)2.3 increases inactivation in Ca(v)2.1. Each mutation 
affects specifically the gating properties of Ca(v)2.1 that remain nevertheless 
modulated by the co-expressed beta 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(v)2.1 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(v)2.1 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(v)2.1 and the 
lack of effect of V421 insertion on inactivation.