title: The familial hemiplegic migraine mutation R192Q reduces G-protein-mediated inhibition of P/Q-type (Ca(V)2.1) calcium channels expressed in human embryonic kidney cells.
abstract: Familial hemiplegic migraine is associated with at least 13 different missense mutations in the alpha1A Ca(2+) channel subunit. Some of these mutations have been shown to affect the biophysical properties of alpha1A currents. To date, no study has examined the influence of such mutations on the G-protein regulation of channel function. Because G-proteins inhibit movement of the voltage sensor, we examined the effects of the R192Q mutation, which neutralizes a positive charge in the first S4 segment. Human wild-type (WT) or R192Q mutant channels were expressed in human embryonic kidney tsA-201 cells along with dopamine D2 receptors. Application of quinpirole induced fast (approximately 1 s), pertussis toxin-sensitive inhibition of alpha1A(WT) and alpha1A(R192Q) Ca(2+) currents, consistent with the activation of a membrane-delimited pathway. alpha1A(WT) Ca(2+) currents were inhibited by 62.9 +/- 0.9 % (n = 27), whereas alpha1A(R192Q) Ca(2+) currents were inhibited by only 47.9 +/- 1.8 % (n = 35; P < 0.001). Concentration-response analysis showed that only the extent of inhibition was affected, with no change in agonist potency (EC(50) = 1 nM). Prepulse facilitation, which is a characteristic of voltage-dependent inhibition, was also reduced by the R192Q mutation. However, the kinetics of facilitation and slow activation were not affected, suggesting that G-protein-Ca(2+) channel affinity was unchanged. These results show that the R192Q mutation reduces the G-protein inhibition of P/Q-type Ca(2+) channels, probably by altering mechanisms by which Gbetagamma subunit binding induces a change in channel gating. Altered G-protein modulation and the consequent reduced presynaptic inhibition may contribute to migraine attacks by favouring a persistent state of hyperexcitability.
authors.affiliation: Merck Sharp and Dohme Research Laboratories, The Neuroscience Research Centre, Terlings Park, Eastwick Road, Harlow, Essex CM20 2QR, UK. karim_melliti@merck.com
authors.forename: Karim
authors.initials: K
authors.lastname: Melliti
authors.forename: Manfred
authors.initials: M
authors.lastname: Grabner
authors.forename: Guy R
authors.initials: GR
authors.lastname: Seabrook
mesh_terms: D020864:Calcium Channels, N-Type / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D002460:Cell Line; D004553:Electric Conductivity; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D007668:Kidney / Q000196:embryology*; D007700:Kinetics; D020325:Migraine with Aura / Q000235:genetics*; D009154:Mutation / Q000502:physiology*; D018408:Patch-Clamp Techniques; D017448:Receptors, Dopamine D2 / Q000502:physiology
chemical_list: D020864:Calcium Channels, N-Type; D019204:GTP-Binding Proteins; D017448:Receptors, Dopamine D2