Myers J M, Tunnicliff G
Laboratory of Neurochemistry, Indiana University School of Medicine, 8600 University Boulevard, Evansville, IN 47712, U.S.A.
Neurochem Int. 1988;12(2):125-9. doi: 10.1016/0197-0186(88)90119-2.
GABA receptor binding to mammalian neuronal membranes has been classified into at least 2 subtypes-GABA(A) and GABA(B) binding sites. In catfish brain GABA(A) receptor sites have previously been demonstrated. Evidence is now presented that under appropriate conditions which rule out GABA(A) receptor binding, [(3)H]GABA binds to membranes prepared from catfish brain. This binding is bicuculline-insensitive but differs enough from mammalian GABA(B) binding to cast some doubt on the idea that GABA(B) receptors exist in catfish brain. Specific binding was detected that was saturable and exhibited a dissociation constant of 4?M. (+/-)Baclofen, a potent inhibitor in rat brain, was a weak inhibitor, producing a maximum of 43% inhibition. This inhibitory effect could be enhanced, however, in the presence of 320 ?M isoguvacine. [(3)H]GABA binding was unaffected by bicuculline. Thus bicuculline-insensitive GABA binding sites exist in catfish brain but they differ in a number of ways from the GABA(B) receptor site found in mammals. Furthermore, a third [(3)H]GABA binding site appears to exist that is both baclofen- and bicuculline-insensitive, yet is inhibited by high concentrations of isoguvacine, a known GABA(A) agonist.
γ-氨基丁酸（GABA）与哺乳动物神经元膜的结合已被至少分为两种亚型——GABA(A)和GABA(B)结合位点。此前已在鲶鱼脑中证实了GABA(A)受体位点。现在有证据表明，在排除GABA(A)受体结合的适当条件下，[³H]GABA与从鲶鱼脑制备的膜结合。这种结合对荷包牡丹碱不敏感，但与哺乳动物的GABA(B)结合有足够差异，这使人对鲶鱼脑中存在GABA(B)受体的观点产生一些怀疑。检测到的特异性结合是可饱和的，解离常数为4μM。(±)巴氯芬是大鼠脑中的一种强效抑制剂，却是一种弱抑制剂，最大抑制率为43%。然而，在存在320μM异鹅肌肽的情况下，这种抑制作用可以增强。[³H]GABA结合不受荷包牡丹碱影响。因此，鲶鱼脑中存在对荷包牡丹碱不敏感的GABA结合位点，但它们在许多方面与哺乳动物中发现的GABA(B)受体位点不同。此外，似乎存在第三个[³H]GABA结合位点，它对巴氯芬和荷包牡丹碱均不敏感，但会被高浓度的异鹅肌肽（一种已知的GABA(A)激动剂）抑制。
