Two mutations linked to nocturnal frontal lobe epilepsy cause use-dependent potentiation of the nicotinic ACh response

J Physiol. 1998 Dec 15;513 ( Pt 3)(Pt 3):655-70. doi: 10.1111/j.1469-7793.1998.655ba.x.


1. We constructed rat homologues (S252F and +L264) of two human alpha4 nicotinic mutations - alpha4(S248F) and alpha4(777ins3) - that have been linked to autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) and co-expressed them with wild-type rat beta2 subunits in Xenopus oocytes. 2. The S252F and +L264 mutations had three common effects on the ACh response. First, they caused use-dependent potentiation of the response during a train of brief 100 nM ACh pulses. Second, they delayed the rise times of the 5-15 nM (+L264) and 30 nM (S252F) ACh responses. Third, they reduced extracellular Ca2+-induced increases in the 30 microM ACh response. 3. Beside these shared effects, the S252F mutation also reduced the channel burst duration measured from voltage-jump relaxations, enhanced steady-state desensitization and reduced the single-channel conductance. In contrast, the +L264 mutation prolonged the channel burst duration, did not affect desensitization and slightly increased single-channel conductance. Neither mutation affected the number of surface receptors measured by antibody binding but the S252F mutation reduced the maximum ACh response. 4. The ACh concentration dependence of use-dependent potentiation and the delay in the rising phase of the mutant ACh response suggest that these effects are caused by a slow unblocking of the closed mutant receptors. Use-dependent potentiation of the mutant response during a series of high-frequency cholinergic inputs to the presynaptic terminal could trigger ADNFLE seizures by suddenly increasing nicotinic-mediated transmitter release.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Algorithms
  • Animals
  • Bridged Bicyclo Compounds, Heterocyclic / metabolism
  • Calcium / pharmacology
  • Electric Stimulation
  • Electrophysiology
  • Epilepsy, Frontal Lobe / genetics*
  • Humans
  • Iodine Radioisotopes
  • Ion Channels / genetics
  • Ion Channels / metabolism
  • Membrane Potentials / physiology
  • Mutation / physiology*
  • Nicotinic Agonists / metabolism
  • Oocytes / metabolism
  • Patch-Clamp Techniques
  • Pyridines / metabolism
  • Rats
  • Receptors, Nicotinic / genetics*
  • Xenopus


  • Bridged Bicyclo Compounds, Heterocyclic
  • Iodine Radioisotopes
  • Ion Channels
  • Nicotinic Agonists
  • Pyridines
  • Receptors, Nicotinic
  • epibatidine
  • Calcium