Department of Physiology and Biophysics, Aarhus University, Ole Worms Allé 1160, DK 8000 Arhus C, Denmark.
Br J Pharmacol. 2010 Feb 1;159(3):636-49. doi: 10.1111/j.1476-5381.2009.00542.x. Epub 2010 Jan 25.
Although picrotoxin is a well-established antagonist of GABA(A) receptors, detailed studies of its action on inhibitory synaptic transmission have not previously been made.
Electrophysiological techniques were used to study the action of picrotoxin on inhibitory postsynaptic currents (IPSCs) evoked in hippocampal neurones, in culture and slice preparations prepared from Wistar rat embryos and juveniles, respectively.
Picrotoxin gradually reduced the amplitude of GABA(A) receptor-mediated eIPSCs in a concentration-dependent manner. This was accompanied by a marked acceleration of the eIPSC decay kinetics, which, in contrast to the effect on amplitude, developed immediately and was completely reversed on washing. The decaying phase of the IPSC could be resolved into two components; 30 microM picrotoxin reduced tau(fast) by 34% and increased its relative amplitude, while tau(slow) was reduced by 38%, and its relative amplitude decreased. The area under the decaying phase of the normalized eIPSC showed an immediate reduction by 36% in 30 microM picrotoxin. With increasing concentrations of picrotoxin, this normalized area converged towards 55% of the control, indicating that the rate of relaxation and block has a finite maximum. This implies that picrotoxin does not act by a pore-occluding mechanism (open-channel blocking), and suggests allosteric stabilization of desensitized receptor states as a more likely alternative. This was corroborated by modelling, based on two established microscopic GABA(A) receptor transition schemes.
Although the identity of the stabilized state has not been determined unequivocally, picrotoxin effectively traps synaptic GABA(A) receptors in a desensitized state.
尽管苦蕈碱是 GABA(A) 受体的一种成熟拮抗剂，但之前并未对其在抑制性突触传递中的作用进行详细研究。
分别使用电生理学技术研究了苦蕈碱在 Wistar 大鼠胚胎和幼体培养和切片制备的海马神经元中诱导的抑制性突触后电流（IPSCs）的作用。
苦蕈碱逐渐以浓度依赖性方式降低 GABA(A) 受体介导的 eIPSCs 的幅度。这伴随着 IPSC 衰减动力学的显著加速，与幅度的影响相反，这种加速立即发生，并在洗涤后完全逆转。IPSC 的衰减相可分为两个分量；30μM 苦蕈碱将 tau(fast) 缩短 34%并增加其相对幅度，而 tau(slow) 缩短 38%，其相对幅度降低。归一化 eIPSC 衰减相的面积在 30μM 苦蕈碱中立即减少 36%。随着苦蕈碱浓度的增加，归一化面积收敛到对照的 55%，表明弛豫和阻断的速度具有有限的最大值。这表明苦蕈碱不是通过孔阻塞机制（通道开放阻断）起作用的，并且暗示变构稳定脱敏受体状态是一种更可能的替代机制。这得到了基于两个已建立的微观 GABA(A) 受体转换方案的建模的证实。
尽管稳定状态的身份尚未明确确定，但苦蕈碱有效地将突触 GABA(A) 受体固定在脱敏状态。
