Martin R J, Valkanov M A
Department of Preclinical Veterinary Sciences, Royal (Dick) School of Veterinary Studies, Summerhall, University of Edinburgh, UK.
Exp Physiol. 1996 Nov;81(6):909-25. doi: 10.1113/expphysiol.1996.sp003992.
Isolated muscle bags from the parasitic nematode Ascaris suum were prepared by collagenase treatment and dissection. Single bags were mounted in a V-shaped plastic pipette for voltage clamp application and intra- and extracellular perfusion. With 'physiological' intra- and extracellular solutions, depolarizing voltage steps from near the normal resting membrane potential, -40 mV, produced in leak-corrected currents, a slowly activating outward current at potentials more positive than -20mV. At the end of the depolarizing pulse there was a slow inward tail current with a reversal potential near -20mV. Hyperpolarizing voltage steps produced an outward current relaxation and an outward tail current with the same reversal potential. The observations can be explained by the presence in the bag of a non-selective cation channel current, Ibcat, that activates spontaneously at the holding potential; depolarization increases opening of the channel and hyperpolarization decreases opening. Bath-applied acetylcholine in concentrations greater than 10(-7) M produced an increase in the amplitude of Ibcat. The effect of acetylcholine was not antagonized or prevented by 100 microM tubocurarine, suggesting the presence of a non-nicotinic acetylcholine receptor. Atropine (100 microM) had no detectable influence on the effect of acetylcholine but the FMRFamide peptide, PF1, in concentrations > 1 microM, reduced the amplitude of Ibcat. Ibcat was maintained when Cs+ was used to replace intra- and extracellular cations, showing that the channels were permeable to Cs+. It is concluded that the bag membrane possesses a slow voltage-activated non-selective cation channel current, Ibcat. The effect of acetylcholine in the presence of nicotinic antagonist indicates the presence of non-nicotinic acetylcholine receptors on the bag membrane. The effect of PF1 indicated the presence of PF1 receptors on the bag membrane.
通过胶原酶处理和解剖制备了来自寄生线虫猪蛔虫的分离肌肉袋。将单个肌肉袋安装在V形塑料移液管中用于电压钳应用以及细胞内和细胞外灌注。使用“生理”细胞内和细胞外溶液，从接近正常静息膜电位-40mV开始的去极化电压阶跃，在经泄漏校正的电流中，在比-20mV更正的电位下产生缓慢激活的外向电流。在去极化脉冲结束时，有一个缓慢的内向尾电流，其反转电位接近-20mV。超极化电压阶跃产生外向电流松弛和具有相同反转电位的外向尾电流。这些观察结果可以通过肌肉袋中存在一种非选择性阳离子通道电流Ibcat来解释，该电流在保持电位下自发激活；去极化增加通道开放，超极化减少通道开放。浴用浓度大于10^(-7)M的乙酰胆碱会使Ibcat的幅度增加。100μM筒箭毒碱不会拮抗或阻止乙酰胆碱的作用，这表明存在非烟碱型乙酰胆碱受体。阿托品（100μM）对乙酰胆碱的作用没有可检测到的影响，但浓度>1μM的FMRF酰胺肽PF1会降低Ibcat的幅度。当用Cs+替代细胞内和细胞外阳离子时，Ibcat得以维持，表明这些通道对Cs+具有通透性。结论是肌肉袋膜具有一种缓慢电压激活的非选择性阳离子通道电流Ibcat。在烟碱拮抗剂存在下乙酰胆碱的作用表明肌肉袋膜上存在非烟碱型乙酰胆碱受体。PF1的作用表明肌肉袋膜上存在PF1受体。
