Nicholson G M, Walsh R, Little M J, Tyler M I
Department of Health Sciences, University of Technology, Sydney, City Campus, Broadway, NSW 2007, Australia.
Pflugers Arch. 1998 Jun;436(1):117-26. doi: 10.1007/s004240050612.
The present study investigates the actions of robustoxin (atracotoxin-Ar1) purified from the venom of the male Sydney funnel-web spider Atrax robustus on sodium channel gating. Using whole-cell patch-clamp techniques the study assessed the actions of robustoxin on tetrodotoxin-resistant (TTX-R) and tetrodotoxin-sensitive (TTX-S) sodium currents in rat dorsal root ganglion cells. Similar to the closely related funnel-web spider toxin versutoxin (delta-atracotoxin-Hv1) from Hadronyche versuta, robustoxin had no effect on TTX-R sodium currents but exerted potent effects on TTX-S sodium currents. The main action of robustoxin was a concentration-dependent slowing or removal of TTX-S sodium current inactivation. This steady-state current was maintained during long-lasting depolarisations at all test potentials. Robustoxin (30 nM) also caused a 13-mV hyperpolarising shift in the voltage midpoint of steady-state sodium channel inactivation (h infinity) leading to a reduced peak current at a holding potential of -80 mV. Moreover there was a steady-state or non-inactivating component present (18% of maximal sodium current) at prepulse potentials that normally inactivate all TTX-S sodium channels (more depolarised than -40 mV). In addition robustoxin produced a significant increase in the repriming kinetics of the sodium channel when channels returned to the resting state following activation. This increase in the rate of recovery of sodium current appears to explain the use-dependent effects on peak sodium current amplitude at high stimulation frequencies. Finally 30 nM robustoxin caused an 11-mV hyperpolarising shift in the voltage dependence of the channel but did not markedly modify tail current kinetics. These actions suggest that robustoxin inhibits conversion of the open state to the inactivated state of TTX-S sodium channels, thus allowing a fraction of the sodium current to remain at membrane potentials at which inactivation is normally complete. Given the recent reclassification of funnel-web spider toxins as atracotoxins, robustoxin should henceforth be known as delta-atracotoxin-Ar1 to reflect this main action on sodium channel inactivation. These present results further support the hypothesis that funnel-web spider toxins interact with neurotoxin receptor site 3 to slow channel inactivation in a manner similar to that of alpha-scorpion and sea anemone toxins.
本研究调查了从雄性悉尼漏斗网蜘蛛Atrax robustus毒液中纯化得到的强劲毒素（atraco毒素 - Ar1）对钠通道门控的作用。该研究使用全细胞膜片钳技术评估了强劲毒素对大鼠背根神经节细胞中河豚毒素抗性（TTX - R）和河豚毒素敏感性（TTX - S）钠电流的作用。与来自Hadronyche versuta的密切相关的漏斗网蜘蛛毒素通用毒素（δ - atracotoxin - Hv1）类似，强劲毒素对TTX - R钠电流没有影响，但对TTX - S钠电流有显著作用。强劲毒素的主要作用是浓度依赖性地减慢或消除TTX - S钠电流的失活。在所有测试电位下的长时间去极化过程中，这种稳态电流得以维持。30 nM的强劲毒素还导致稳态钠通道失活（h∞）的电压中点发生13 mV的超极化偏移，导致在 - 80 mV的钳制电位下峰值电流降低。此外，在通常使所有TTX - S钠通道失活的预脉冲电位（比 - 40 mV更正极）下，存在一个稳态或非失活成分（最大钠电流的18%）。另外，当通道在激活后恢复到静息状态时，强劲毒素使钠通道的再激活动力学显著增加。钠电流恢复速率的这种增加似乎解释了在高刺激频率下对峰值钠电流幅度的使用依赖性效应。最后，30 nM的强劲毒素使通道的电压依赖性发生11 mV的超极化偏移，但未显著改变尾电流动力学。这些作用表明，强劲毒素抑制TTX - S钠通道从开放状态向失活状态的转变，从而使一部分钠电流在正常情况下失活完全的膜电位下仍能保留。鉴于最近漏斗网蜘蛛毒素被重新分类为atraco毒素，从今往后强劲毒素应被称为δ - atracotoxin - Ar1，以反映其对钠通道失活的这一主要作用。目前的这些结果进一步支持了这样的假设，即漏斗网蜘蛛毒素与神经毒素受体位点3相互作用，以类似于α - 蝎毒素和海葵毒素的方式减慢通道失活。
