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.
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Authors | Nivalda Rodrigues-Pinguet, Li Jia, Maureen Li, Antonio Figl, Alwin Klaassen, Anthony Truong, Henry A Lester, Bruce N Cohen |
Journal | The Journal of physiology
(J Physiol)
Vol. 550
Issue Pt 1
Pg. 11-26
(Jul 01 2003)
ISSN: 0022-3751 [Print] England |
PMID | 12754307
(Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)
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Chemical References |
- Bridged Bicyclo Compounds, Heterocyclic
- Chloride Channels
- Nicotinic Agonists
- Pyridines
- Receptors, Nicotinic
- nicotinic receptor alpha4beta2
- Barium
- epibatidine
- Acetylcholine
- Calcium
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Topics |
- Acetylcholine
(pharmacology)
- Amino Acid Sequence
(genetics)
- Animals
- Artifacts
- Barium
(pharmacology)
- Bridged Bicyclo Compounds, Heterocyclic
(metabolism)
- Calcium
(pharmacology, physiology)
- Cell Membrane
(metabolism)
- Chloride Channels
(physiology)
- Circadian Rhythm
(genetics)
- Electric Conductivity
- Epilepsy, Frontal Lobe
(genetics)
- Genes, Dominant
- Homeostasis
- Molecular Sequence Data
- Mutation
(genetics, physiology)
- Nicotinic Agonists
(metabolism)
- Oocytes
- Pyridines
(metabolism)
- Rats
- Reaction Time
- Receptors, Nicotinic
(drug effects, genetics, metabolism)
- Xenopus laevis
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