Jackel C, Krenz W, Nagy F
J Exp Biol. 1994 Jun;191(1):167-93. doi: 10.1242/jeb.191.1.167.
Neurones were dissociated from thoracic ganglia of embryonic and adult lobsters and kept in primary culture. When gamma-aminobutyric acid (GABA) was applied by pressure ejection, depolarizing or hyperpolarizing responses were produced, depending on the membrane potential. They were accompanied by an increase in membrane conductance. When they were present, action potential firing was inhibited. The pharmacological profile and ionic mechanism of GABA-evoked current were investigated under voltage-clamp with the whole-cell patch-clamp technique. The reversal potential of GABA-evoked current depended on the intracellular and extracellular Cl- concentration but not on extracellular Na+ and K+. Blockade of Ca2+ channels by Mn2+ was also without effect. The GABA-evoked current was mimicked by application of the GABAA agonists muscimol and isoguvacine with an order of potency muscimol>GABA>isoguvacine. cis-4-aminocrotonic acid (CACA), a folded and conformationally restricted GABA analogue, supposed to be diagnostic for the vertebrate GABAC receptor, also induced a bicuculline-resistant chloride current, although with a potency about 10 times lower than that of GABA. The GABA-evoked current was largely blocked by picrotoxin, but was insensitive to the GABAA antagonists bicuculline, bicuculline methiodide and SR 95531 at concentrations of up to 100 µmol l-1. Diazepam and phenobarbital did not exert modulatory effects. The GABAB antagonist phaclophen did not affect the GABA-induced current, while the GABAB agonists baclophen and 3-aminopropylphosphonic acid (3-APA) never evoked any response. Our results suggest that lobster thoracic neurones in culture express a chloride-conducting GABA-receptor channel which conforms to neither the GABAA nor the GABAB types of vertebrates but shows a pharmacology close to that of the novel GABAC receptor described in the vertebrate retina.
从胚胎和成体龙虾的胸神经节中分离出神经元，并进行原代培养。当通过压力喷射施加γ-氨基丁酸（GABA）时，根据膜电位会产生去极化或超极化反应。它们伴随着膜电导的增加。当这些反应出现时，动作电位发放受到抑制。采用全细胞膜片钳技术在电压钳条件下研究了GABA诱发电流的药理学特性和离子机制。GABA诱发电流的反转电位取决于细胞内和细胞外的Cl⁻浓度，而不取决于细胞外的Na⁺和K⁺。Mn²⁺对Ca²⁺通道的阻断也没有影响。应用GABAA激动剂蝇蕈醇和异鹅去氧胆酸可模拟GABA诱发的电流，其效力顺序为蝇蕈醇>GABA>异鹅去氧胆酸。顺式-4-氨基巴豆酸（CACA）是一种折叠且构象受限的GABA类似物，被认为是脊椎动物GABAC受体的诊断试剂，它也能诱导一种荷包牡丹碱抗性氯电流，尽管其效力比GABA低约10倍。GABA诱发的电流在很大程度上被印防己毒素阻断，但在浓度高达100 μmol l⁻¹时对GABAA拮抗剂荷包牡丹碱、甲基荷包牡丹碱和SR 95531不敏感。地西泮和苯巴比妥没有发挥调节作用。GABAB拮抗剂巴氯芬不影响GABA诱导的电流，而GABAB激动剂巴氯芬和3-氨基丙基膦酸（3-APA）从未引起任何反应。我们的结果表明，培养的龙虾胸神经元表达一种氯离子传导的GABA受体通道，它既不符合脊椎动物的GABAA型也不符合GABAB型，但药理学特性与脊椎动物视网膜中描述的新型GABAC受体相近。
