Mutations linked to familial hemiplegic migraine located in the pore region of P/Q calcium channels (CAV2.1): Effect on channel conductance and selectivity

Mutations at the gene encoding alpha12.1 subunits of P/Q Ca2+ channels cause a group of human neurologic disorders including familial hemiplegic migraine (FHM). Four mutations linked to FHM lead to aminoacid substitutions in the pore region: T666M and V1457L are close to two of the glutamate residues forming the high-affinity Ca2+ binding site in the selectivity filter; V714A and I1811L are at the intracellular ends of IIS6 and IVS6. Previously, we reported a reduced single channel conductance for mutants T666M and V714A and a wild-type (wt) conductance for mutant I1811L. We have now studied the single channel properties of mutant V1457L, and the effect of the pore mutations on channel selectivity, after transient expression of wt and mutant human CaV2.1 channels in HEK293 cells. Mutation V1457L reduces the single channel conductance and shifts its activation curve to more negative voltages. Judging from the reversal potentials of whole-cell Ca2+ currents, both mutations T666M and V1457L reduce the channel selectivity for divalent with respect to monovalent ions, whereas mutation V714A does not affect selectivity. The single channel conductance for Na+ ions is not affected by mutations T666M and V1457L, whereas it is reduced by mutation V714A. High-affinity binding of divalent ions is not altered by mutation T666M. Our data suggest that mutations T666M and V1457L selectively decrease the divalent ion flux by reducing the effectiveness with which two divalent ions interact in the selectivity filter.