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We suggest that a dysregulation of energy metabolism in the brain of genetic absence epilepsy rats from Strasbourg (GAERS) could create a specific cerebral environment that would favor the expression of spike-and-wave discharges (SWD) in the thalamocortical loop, largely dependent on glutamatergic and gamma-aminobutyric acid (GABA)-ergic neurotransmissions. We tested several aspects of metabolic activity in the brain of GAERS compared to a genetic strain of nonepileptic (NE) rats. Glucose metabolism was higher in all brain regions of GAERS compared to those of NE rats along the whole glycolytic and aerobic pathways, as assessed by regional histochemical measurement of lactate dehydrogenase and cytochrome oxidase activities. Branched-chain amino acids (BCAA) and alpha-ketoisocaproate (alpha-KIC), the ketoacid of leucine, when injected intraperitoneally, increased the number of SWD in GAERS but had only a slight effect on their duration. These data speak in favor of a BCAA- or alpha-KIC-induced change in neuronal excitability. Leucine and alpha-KIC decreased the concentration of glutamate in thalamus and cortex without affecting GABA concentrations. Thus, BCAA and alpha-KIC, by decreasing glutamatergic neurotransmission, could favor GABAergic neurotransmission, which is known to increase the occurrence of seizures in GAERS. Finally, the transport of [1-(14)C]alpha-KIC in freshly isolated cortical neurons was lower in GAERS than in NE rats, and this difference was shown to be of metabolic origin. The addition of gabapentin, a specific inhibitor of BCAA transaminase (BCAT), reduced the transport of [1-(14)C]alpha-KIC in GAERS and NE rats to a level that became identical in both strains. This strain-dependent change was not related to a difference in the activity of BCAT, which was identical in GAERS and NE rats. The exact origin of this apparent metabolic dysregulation of energy metabolism in GAERS that could underlie the origin of seizures in that strain remains to be explored further., (Copyright 2001 Wiley-Liss, Inc.)

The purpose of this study was to investigate the effects exerted by thiol-modifying reagents on themitochondrial sulfonylurea receptor. The thiol-oxidizing agents (timerosal and 5, 5'-dithio-bis(2-nitrobenzoic acid)) were found to produce a large inhibition (70% to 80%) of specific binding of [(3)H]glibenclamide to the beef heart mitochondrial membrane. Similar effects were observed with membrane permeable (N-ethylmaleimide) and non-permeable (mersalyl) thiol modifying agents. Glibenclamide binding was also decreased by oxidizing agents (hydrogen peroxide) but not by reducing agents (reduced gluthatione, dithiothreitol and the 2,3-dihydroxy-1,4-dithiolbutane). The results suggest that intact thiol groups, facing the mitochondrial matrix, are essential for glibenclamide binding to the mitochondrial sulfonylurea receptor., (Copyright 1999 Academic Press.)

The transport of L-carnitine (4-N-trimethylammonium-3-hydroxybutyric acid) was studied with a primary culture of porcine brain capillary endothelial cells (BCEC) as an in vitro model of the blood-brain barrier. The measurements with suspended cells and cell monolayers allowed to distinguish a polarized transport phenomena. The part of the BCEC cells exposed to the medium (apical membrane) accumulated carnitine by a sodium-independent, saturable (Km=28 microM) system, with k=0.018 min-1. Exposure of the basolateral part revealed a presence of a facilitated diffusion process. Carnitine uptake through the saturable system was inhibited by butyrobetaine. Acylcarnitines and choline have no effect on the carnitine accumulation in suspended cells, a process diminished by phenylalanine, leucine, and L system inhibitor. This points to the possibility that carnitine enters through the basolateral membrane using amino acid transporting systems. A different, novel system is postulated to operate in the apical part of the plasma membrane of BCEC., (Copyright 1997 Academic Press.)

Mitochondria from several tissues contain a potassium-specific channel similar to the ATP-regulated K+ (K ATP) channel of the plasma membrane. The mitochondrial channel shares with the plasma membrane K ATP channel the sensitivity to sulfonylurea derivatives and some other blockers as well as to channel openers of diverse chemical character. In contrast to the plasma membrane channel, which is blocked by free ATP, the mitochondrial K ATP channel reconstituted into liposomes requires the ATP-Mg complex for inhibition. The mitochondrial K ATP channel, possibly in a concerted action with other K+ permeability pathways, plays an important role in mitochondrial volume control. Its function in the regulation of the components of the protonmotive force is also suggested.

N,N'-Dicyclohexylcarbodiimide (DCCD) inhibits the activity of ubiquinol-cytochrome c reductase in the isolated and reconstituted mitochondrial cytochrome b-c1 complex. In proteoliposomes containing b-c1 complex DCCD inhibits equally electron flow and proton translocation catalyzed by the enzyme. In both isolated and reconstituted systems the inhibitory effect is accompanied by structural alterations in the polypeptide pattern of the enzyme consistent with cross-linking between subunits V and VII. The kinetics of inhibition of enzymic activity correlates with that of the cross-linking, suggesting that the two phenomena may be coupled. Binding of [14C] DCCD to both isolated and reconstituted enzyme was also observed, though it was not correlated kinetically with the inhibition.