The Efficacy of the GABA[underline]A[/underline] Receptor Endogenous Phosphorylation Is Decreased in the Human Epileptogenic Tissue.
Abstract number :
2.033
Submission category :
Year :
2001
Submission ID :
2711
Source :
www.aesnet.org
Presentation date :
12/1/2001 12:00:00 AM
Published date :
Dec 1, 2001, 06:00 AM
Authors :
R. Pumain, PhD, U109, Inserm, Paris, France; I. Kurcewicz, U109, Inserm, Paris, France; F. Minier, PhD, Neurosciences, Un. de Rennes, Rennes, France; J. Louvel, PhD, U109, Inserm, Paris, France; B. Turak, MD, U109, Inserm, Paris, France; B. Devaux, MD, Ne
RATIONALE: Maintenance of GABA currents requires that the type A receptors (GABAA-R) be phosphorylated by a specific, closely associated endogenous kinase. We have shown in the bovine cortex, that the endogenous kinase was the glyceraldehyde-3-phosphate deshydrogenase (GAPDH), an enzyme of the glycolysis. This protein has been shown to specifically phosphorylate of the [alpha]1 subunit of purified GABAA-R. Run-down of GABA induced currents of acutely dissociated rat neocortical neurons was decreased or prevented by the protein or its specific substrate, glyceraldehyde-3-phosphate (G-3-P), and accelerated by iodacetamide, which inactivates GAPDH.
METHODS: We have tested whether neurons from cortectomies taken from epileptic patients undergoing neurosurgery for therapeutic reasons revealed a similar modulation of the GABAA responses.
RESULTS: Phosphorylation of the [alpha]1 subunit of GABAA-R was significantly reduced in the epileptogenic cortex (40%), compared to post-mortem control human cortex. This feature was not related to a reduced number of GABAA-R in the epileptogenic tissue since no correlation could be found between incorporation of phosphate on [alpha]1 subunits and binding to [3H flunitrazepam] on the same subunits. Patch-clamp experiments on acutely dissociated cells from epileptogenic human tissue revealed that the run down of GABAA responses was faster in the human tissue when compared to the normal rat cortex. After introduction in the intracellular perfusate, G-3-P markedly reduced the run down of the GABAA responses. However, its efficacy was less than in the control rat cortex. Iodoacetamide accelerated the run down.
CONCLUSIONS: These experiments show that GAPDH is very likely the endogenous kinase phosphorylating the [alpha]1 subunit of the GABAA-R in humans, reducing run-down of the GABAA responses. Phosphorylation of the [alpha]1 subunit appears to be less efficient in the epileptic than in control tissue, which can promote propagation of seizures. In addition, this feature parallels the hypometabolism associated with the epileptogenic zone in epileptic patients.