Characterisation of [3H]gabapentin binding to a novel site in rat brain: homogenate binding studies.
The binding characteristics of [3H]gabapentin, the radiolabelled analogue of the novel anticonvulsant gabapentin (1-(aminomethyl)cyclohexaneacetic acid) were studied using purified synaptic plasma membranes prepared from rat cerebral cortex. In 10 mM HEPES buffer [3H]gabapentin bound to a single population of sites with high affinity (KD = 38 +/- 2.8 nM) with a maximum binding capacity of 4.6 +/- 0.4 pmol/mg protein, reaching equilibrium after 30 min at 20 degrees C. This novel site was unique to the central nervous system with little or no specific [3H]gabapentin being measurable in a range of peripheral tissues. Binding was potently inhibited by a range of gabapentin analogues and 3-alkyl substituted gamma-aminobutyric acid (GABA) derivates although GABA itself and the selective GABAB receptor ligand baclofen, were only weakly active. Gabapentin itself (IC50 = 80 nM) and 3-isobutyl GABA (IC50 = 80 nM) which also has anticonvulsant properties, showed the highest affinity for the binding site. Of a wide range of other pharmacologically active compounds only the polyamines spermine and spermidine influenced [3H]gabapentin binding, with both compounds producing a maximum of 50% inhibition of specific binding. Magnesium ions produced a similar pattern of inhibition but the effect of the polyamines and magnesium ions were not additive. The data provide evidence for the existence in brain of a novel binding site that may mediate the anticonvulsant effects of gabapentin and other potential anticonvulsant compounds.
Suman-Chauhan
N
N
Parke-Davis Neuroscience Research Centre, Addenbrookes Hospital Site, Cambridge, UK.
Webdale
L
L
Hill
D R
DR
Woodruff
G N
GN
D000085:Acetates / Q000378:metabolism* / Q000494:pharmacology; D000588:Amines; D000596:Amino Acids / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D000927:Anticonvulsants / Q000378:metabolism* / Q000494:pharmacology; D001418:Baclofen / Q000378:metabolism; D001665:Binding Sites / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D003509:Cyclohexanecarboxylic Acids; D000077206:Gabapentin; D006863:Hydrogen-Ion Concentration; D051381:Rats; D011963:Receptors, GABA-A / Q000378:metabolism; D018009:Receptors, Glycine; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D017981:Receptors, Neurotransmitter / Q000378:metabolism; D013095:Spermidine / Q000494:pharmacology; D013096:Spermine / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000031:analogs & derivatives / Q000494:pharmacology
D000085:Acetates; D000588:Amines; D000596:Amino Acids; D000927:Anticonvulsants; D003509:Cyclohexanecarboxylic Acids; D011963:Receptors, GABA-A; D018009:Receptors, Glycine; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter; D013096:Spermine; D005680:gamma-Aminobutyric Acid; D000077206:Gabapentin; D001418:Baclofen; D013095:Spermidine