Five ADNFLE mutations reduce the Ca2+ dependence of the mammalian α4β2 acetylcholine response

• Published in: The Journal of physiology 2003-07, Vol.550 (1), p.11
• Main Authors: Nivalda Rodrigues-Pinguet, Li Jia, Maureen Li, Antonio Figl, Alwin Klaassen, Anthony Truong, Henry A Lester, Bruce N Cohen
• Format: Article
• Language: English
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2003.036681

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 (α4 or β2), and studied the Ca 2+ dependence of their ACh responses. All the mutations significantly reduced 2 mM Ca 2+ -induced increases in the 30 μM 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 Ca 2+ -activated Cl − currents. The S256L mutation also abolished 2 mM Ba 2+ 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 μM. Co-expression of the V262M mutation with a mutation (E180Q) that abolished Ca 2+ potentiation resulted in 2 mM Ca 2+ block, rather than potentiation, of the 30 μM ACh response, suggesting that the ADNFLE mutations reduce Ca 2+ potentiation by enhancing Ca 2+ block of the α4β2 nAChR. Ca 2+ modulation may prevent presynaptic α4β2 nAChRs from overstimulating glutamate release at central excitatory synapses during bouts of synchronous, repetitive activity. Reducing the Ca 2+ dependence of the ACh response could trigger seizures by increasing α4β2-mediated glutamate release during such bouts.