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Mutations linked to generalized epilepsy in humans reduce GABA(A) receptor current
Robert L Macdonald1, Matt T Bianchi, Matt T Bianch
1Department of Neurology, Vanderbilt University, Nashville, TN 37212, USA. Robert.Macdonald@vanderbilt.edu
Experimental Neurology
|November 5, 2003
Summary
Mutations in the gamma2 subunit of GABA(A) receptors can cause familial epilepsy. The R43Q mutation reduces receptor surface expression, while K289M accelerates current deactivation, impacting neuronal inhibition differently.
Area of Science:
- Neuroscience
- Molecular Biology
- Genetics
Background:
- Familial epilepsy is linked to mutations in the gamma2 subunit of GABA(A) receptors.
- Previous studies showed R43Q abolished diazepam enhancement and K289M decreased current amplitudes.
Purpose of the Study:
- To investigate the functional effects of gamma2 subunit mutations (R43Q and K289M) on GABA(A) receptor currents.
- To elucidate the mechanisms by which these mutations contribute to familial epilepsy.
Main Methods:
- Expressing mutated gamma2 subunits with alpha1 and beta3 subunits in human embryonic kidney cells.
- Utilizing single channel recording and concentration jump techniques.
- Analyzing current activation, desensitization, deactivation, and single channel properties.
Main Results:
- Neither mutation altered activation or desensitization rates during prolonged GABA application.
- K289M mutation accelerated deactivation, suggesting altered gating efficacy.
- R43Q mutation did not affect diazepam potentiation but reduced current amplitudes, likely due to decreased surface expression.
- The R43Q mutation did not alter diazepam potentiation but resulted in smaller current amplitudes, suggesting reduced surface expression of functional receptors.
Conclusions:
- The R43Q and K289M gamma2 subunit mutations contribute to familial epilepsy through distinct mechanisms.
- Normal neuronal inhibition depends on both the peak amplitude and time course of inhibitory postsynaptic currents (IPSCs).