Binding of [3H]alpha-dihydropicrotoxinin, a gamma-aminobutyric acid synaptic antagonist, to rat brain membranes.
Binding of [3H]alpha-dihydropicrotoxinin, a gamma-aminobutyric acid synaptic antagonist, to rat brain membranes.
复制标题
[3H]α-二氢印防己毒素（一种 γ-氨基丁酸突触拮抗剂）与大鼠脑膜的结合。
作者：
M. Ticku;M. Ban;R. Olsen
α-二氢苦毒素（α-Dihydropicrotoxinin，α-Dihydropicrotoxinin）具有与苦毒素相似的药理活性，能引起惊厥，抑制γ-氨基丁酸在节肢动物肌肉和脊椎动物中枢神经系统的突触反应，可作为表征哺乳动物脑内γ-氨基丁酸受体-离子载体功能的探针。[3H]合成了α-二氢苦毒素，发现其与大鼠脑匀浆的颗粒部分快速、可逆、可饱和结合，表观KD为1-2 µM。结合位点显示出与推测的γ-氨基丁酸受体结合位点相似的亚细胞以及脑区域分布，与突触后膜位置一致。二氢苦毒素结合位点的密度约为5 pmol/mg蛋白质，或130 ± 20 pmol/g湿脑，其在γ-氨基丁酸受体位点数量的2倍范围内。6种印防己毒素类似物的抗惊厥活性与抑制结合的效价具有良好的相关性，而其他一些抗惊厥和抗惊厥药物则抑制了这种结合，提示结合位点可能与药理作用有关。γ-氨基丁酸（高达1 mM）和蝇蕈醇（0.1 mM）不影响结合。由于同样发现印苦毒素不抑制γ-氨基丁酸与脑中受体位点的结合，因此结果支持印苦毒素通过结合在不同于γ-氨基丁酸识别位点的位点来抑制γ-氨基丁酸突触的解释。印苦毒素结合位点可能与调节氯渗透性并将γ-氨基丁酸识别位点（受体）相互作用转化为生理反应的大分子相关。
α-Dihydropicrotoxinin, which has a pharmacological activity similar to that of picrotoxin in producing convulsions and inhibiting the synaptic responses of γ-aminobutyric acid in arthropod muscle and the vertebrate central nervous system, was investigated as a possible probe for characterizing γ-aminobutyric acid receptor-ionophore function in mammalian brain. [3H]α-Dihydropicrotoxinin was synthesized and found to bind rapidly, reversibly, and in a saturable fashion to particulate fractions of rat brain homogenates, with an apparent KD of 1-2 µM. The binding sites showed a similar subcellular as well as brain regional distribution to presumed γ-aminobutyric acid receptor binding sites, consistent with a postsynaptic membrane location. The density of dihydropicrotoxinin binding sites was about 5 pmoles/mg protein, or 130 ± 20 pmoles/g of wet brain, which is within a factor of 2 of the number of γ-aminobutyric acid receptor sites. Six picrotoxin analogues showed an excellent correlation between convulsant activity and potency in inhibiting binding, and some other convulsant and anticonvulsant drugs inhibited the binding, suggesting that the binding sites may be related to the pharmacological effects. γ-Aminobutyric acid (up to 1 mM) and muscimol (0.1 mM) did not affect the binding. Since picrotoxinin has likewise been found not to inhibit γ-aminobutyric acid binding to receptor sites in brain, the results support the interpretation that picrotoxinin inhibits γ-aminobutyric acid synapses by binding at a site distinct from the γ-aminobutyric acid recognition site. The picrotoxinin binding sites are likely to be related to macromolecules that regulate chloride permeability and translate the γ-aminobutyric acid recognition site (receptor) interaction into the physiological response.