title: Five ADNFLE mutations reduce the Ca2+ dependence of the mammalian alpha4beta2 acetylcholine response.
abstract: Five nicotinic acetylcholine receptor (nAChR) mutations are currently linked to autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE). The similarity of their clinical symptoms suggests that a common functional anomaly of the mutations underlies ADNFLE seizures. To identify this anomaly, we constructed rat orthologues (S252F, +L264, S256L, V262L, V262M) of the human ADNFLE mutations, expressed them in Xenopus oocytes with the appropriate wild-type (WT) subunit (alpha4 or beta2), and studied the Ca2+ dependence of their ACh responses. All the mutations significantly reduced 2 mM Ca2+-induced increases in the 30 microM ACh response (P < 0.05). Consistent with a dominant mode of inheritance, this reduction persisted in oocytes injected with a 1:1 mixture of mutant and WT cRNA. BAPTA injections showed that the reduction was not due to a decrease in the secondary activation of Ca2+-activated Cl- currents. The S256L mutation also abolished 2 mM Ba2+ potentiation of the ACh response. The S256L, V262L and V262M mutations had complex effects on the ACh concentration-response relationship but all three mutations shifted the concentration-response relationship to the left at [ACh] >= 30 microM. Co-expression of the V262M mutation with a mutation (E180Q) that abolished Ca2+ potentiation resulted in 2 mM Ca2+ block, rather than potentiation, of the 30 microM ACh response, suggesting that the ADNFLE mutations reduce Ca2+ potentiation by enhancing Ca2+ block of the alpha4beta2 nAChR. Ca2+ modulation may prevent presynaptic alpha4beta2 nAChRs from overstimulating glutamate release at central excitatory synapses during bouts of synchronous, repetitive activity. Reducing the Ca2+ dependence of the ACh response could trigger seizures by increasing alpha4beta2-mediated glutamate release during such bouts.
authors.affiliation: Division of Biomedical Sciences, University of California, Riverside, CA 92521-0121, USA.
authors.forename: Nivalda
authors.initials: N
authors.lastname: Rodrigues-Pinguet
authors.forename: Li
authors.initials: L
authors.lastname: Jia
authors.forename: Maureen
authors.initials: M
authors.lastname: Li
authors.forename: Antonio
authors.initials: A
authors.lastname: Figl
authors.forename: Alwin
authors.initials: A
authors.lastname: Klaassen
authors.forename: Anthony
authors.initials: A
authors.lastname: Truong
authors.forename: Henry A
authors.initials: HA
authors.lastname: Lester
authors.forename: Bruce N
authors.initials: BN
authors.lastname: Cohen
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D016477:Artifacts; D001464:Barium / Q000494:pharmacology; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D018118:Chloride Channels / Q000502:physiology; D002940:Circadian Rhythm / Q000235:genetics*; D004553:Electric Conductivity; D017034:Epilepsy, Frontal Lobe / Q000235:genetics*; D005799:Genes, Dominant; D006706:Homeostasis; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics / Q000502:physiology; D018722:Nicotinic Agonists / Q000378:metabolism; D009865:Oocytes; D011725:Pyridines / Q000378:metabolism; D051381:Rats; D011930:Reaction Time; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D019086:Bridged Bicyclo Compounds, Heterocyclic; D018118:Chloride Channels; D018722:Nicotinic Agonists; D011725:Pyridines; D011978:Receptors, Nicotinic; C403531:nicotinic receptor alpha4beta2; D001464:Barium; C082748:epibatidine; D000109:Acetylcholine; D002118:Calcium