PHARMACOLOGICAL STUDY OF GABA RECEPTORS ON ECHINODERM SMOOTH MUSCLE

最近在PSU Abington的实验室进行的机械研究 1998年春，大学的研究表明，GABA对 控制乙酰胆碱诱导的海参平滑肌收缩。 GABA和GABA激动剂引起剂量依赖性舒张， 相反，GABA拮抗剂刺激收缩。 是否 GABA受体位于支配肌肉的突触前神经元上， 或突触后的肌肉细胞还有待观察 但很明显的是平滑肌对这两者都有反应 GABA A和B受体药物。 在布拉迪斯拉发区域中心进行的实验 1998年7月使用自参考钙电极直接镜像 上述机械研究，以便相关性可以 肌膜钙流和肌肉收缩力之间的关系， 对ACh、GABA和GABA A和B受体处理的反应 拮抗剂/激动剂。 BRC的第一系列实验 使用钙选择性电极显示钙通量 GABA处理可降低ACh刺激的神经元数量。 这些数据在 与我早期的力学数据一致， GABA处理使收缩减少约20%。 巴氯芬， GABA B激动剂，同样减少乙酰胆碱诱导的钙流。 一 据报道，GABA和巴氯芬的作用机制是通过刺激 钙依赖性钾通道，一种被蜂毒肽作用阻断的通道 (bee毒液）。 用维生素A治疗大大降低了 GABA或巴氯芬的浓度。 用法克氯芬（一种GABA B受体拮抗剂）治疗， GABA和巴氯芬（如apamin）的活性， 提示GABA B受体的存在， LMBW的收缩性。 2-羟苯氯芬或苯氯芬（均为GABA B拮抗剂）刺激钙流;这意味着这些 拮抗剂要么阻断肌肉本身的GABA受体， 使肌肉更加兴奋，或者他们阻止了GABA 胆碱能运动神经元上的受体，从而释放它们 从紧张性抑制，并导致更多的乙酰胆碱释放在 神经肌肉接头 机械研究表明，GABA A 受体拮抗剂荷包牡丹碱引起了巨大的持续收缩 的LMBW。 这一发现与钙选择性 电极，荷包牡丹碱刺激了一个大的钙通量， 用GABA治疗后， 结论性数据不可能 从蝇蕈醇（一种GABA A激动剂）的实验中获得， 似乎使电极不稳定。

Recent mechanical studies conducted in my lab at PSU Abington College in the spring of 1998 showed that GABA exerted an inhibitory control over ACh-induced contractions of holothurian smooth muscle. GABA and GABA agonists caused dose-dependent relaxation, while conversely, GABA antagonists stimulated contractions. Whether the GABA receptors lie on the pre-synaptic neurons innervating the muscle, or post-synaptically on the muscle cells themselves remains to be seen but what was clear was that the smooth muscle was responsive to both GABA A and B receptors drugs. Experiments conducted at the BRC in the July 1998 using self-referencing calcium electrodes directly mirrored those aforementioned mechanical studies so that a correlation could be made between sarcolemmal calcium flux and muscle contractility in response to treatment with ACh, GABA and the GABA A and B receptor antagonists/agonists. The first series of experiments at the BRC using the calcium-selective electrodes showed that calcium flux stimulated by ACh was reduced treatment with GABA. This data was in concert with my earlier mechanical data revealing that ACh-induced contractions were reduced by roughly 20% by GABA treatment. Baclofen, a GABA B agonist, similarly reduced ACh-induced calcium flux. One reported mechanism by which GABA and baclofen acts is by stimulating the Ca-dependent K channel, a channel blocked by the action of apamin (bee venom). Treatment with apamin greatly reduced the effectiveness of GABA or baclofen as measured by the calcium-selective electrodes. Treatment with phaclofen, a GABA B receptor antagonist, reduced the activity of both GABA and baclofen (like apamin) which strongly suggests the presence of GABA B receptors in regulating the contractility of the LMBW. 2-hydroxysaclofen or phaclofen (both GABA B antagonists) stimulated calcium flux; this implies that these antagonists either blocked GABA receptors on the muscle itself thus rendering the muscle more excitable, or that they blocked GABA receptors on cholinergic motor neurons upstream thereby releasing them from tonic inhibition and resulting in more ACh release at the neuromuscular junction. Mechanical studies showed that GABA A receptor antagonist, bicuculline, caused a huge sustained contraction of the LMBW. Corroborating this finding with the calcium-selective electrodes, bicuculline stimulated a large calcium flux that was suppressed by treatment with GABA. Conclusive data could not be obtained from experiments with muscimol, a GABA A agonists, as it appeared to destablize the electrode.