PHARMACOLOGICAL STUDY OF GABA RECEPTORS ON ECHINODERM SMOOTH MUSCLE

最近在我在PSU阿宾顿的实验室进行的力学研究 1998年春的大学研究表明，GABA发挥了抑制作用 对ACh引起的海参肌肉收缩的控制。 GABA和GABA激动剂引起剂量依赖的松弛，而 相反，GABA拮抗剂刺激收缩。无论是 GABA受体位于支配肌肉的突触前神经元上， 或突触后对肌肉细胞本身的影响仍有待观察 但有一点是清楚的，那就是平滑肌对这两种物质都有反应 GABA A和B受体药物。在BRC进行的实验 1998年7月使用自参比钙电极直接镜像 那些前述的力学研究，因此相关性可能是 心肌细胞膜钙流量与肌肉收缩能力之间的关系 ACh、GABA和GABA A、B受体对治疗的反应 拮抗剂/激动剂。BRC的第一系列实验 使用钙选择电极显示，钙通量 ACh刺激可被GABA抑制。这一数据是在 与我早先的机械数据显示ACh诱导的 通过GABA治疗，宫缩减少了大约20%。巴氯芬， 一种GABAB激动剂，类似地减少ACh诱导的钙流动。一 已报道的GABA和巴氯芬的作用机制是通过刺激 钙依赖性钾通道，一种被载脂蛋白作用所阻断的通道 (蜂毒)。阿帕明的治疗大大降低了疗效。 用钙选择电极测量的GABA或巴氯芬的浓度。 用GABA B受体拮抗剂Phaclofen治疗后， GABA和巴氯芬(如阿帕明)的活性 提示GABA B受体的存在在调节 LMBW的收缩性能。2-羟基沙洛芬或苯氯芬(均为GABA B受体拮抗剂)刺激钙离子流动；这意味着这些 拮抗剂或者阻断肌肉本身上的GABA受体，从而 使肌肉更容易兴奋，或者它们阻止了GABA 上游运动神经元上的胆碱能受体，从而释放它们 从紧张性抑制，并导致更多的ACh释放 神经肌肉接头。力学研究表明，GABA A 受体拮抗剂荷包牡丹碱引起巨大的持续性收缩 LMBW的。用选择性钙证实了这一发现 电极，荷包牡丹碱刺激了大量的钙通量，这是 用GABA治疗后被抑制。结论数据不可能是 从使用GABA A激动剂麝香酚的实验中获得，因为它 似乎破坏了电极的稳定性。

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.