Rokni Dan, Hochner Binyamin
Department of Neurobiology, Institute of Life Sciences, and the Interdisciplinary Center for Neuronal Computation, Hebrew University, Jerusalem 91904, Israel.
J Neurophysiol. 2002 Dec;88(6):3386-97. doi: 10.1152/jn.00383.2002.
The octopus arm provides a unique model for neuromuscular systems of flexible appendages. We previously reported the electrical compactness of the arm muscle cells and their rich excitable properties ranging from fast oscillations to overshooting action potentials. Here we characterize the voltage-activated ionic currents in the muscle cell membrane. We found three depolarization-activated ionic currents: 1) a high-voltage-activated L-type Ca(2+) current, which began activating at approximately -35 mV, was eliminated when Ca(2+) was substituted by Mg(2+), was blocked by nifedipine, and showed Ca(2+)-dependent inactivation. This current had very rapid activation kinetics (peaked within milliseconds) and slow inactivation kinetics (tau in the order of 50 ms). 2) A delayed rectifier K(+) current that was totally blocked by 10 mM TEA and partially blocked by 10 mM 4-aminopyridine (4AP). This current exhibited relatively slow activation kinetics (tau in the order of 15 ms) and inactivated only partially with a time constant of 150 ms. And 3) a transient A-type K(+) current that was totally blocked by 10 mM 4AP and was partially blocked by 10 mM TEA. This current exhibited very fast activation kinetics (peaked within milliseconds) and inactivated with a time constant in the order of 60 ms. Inactivation of the A-type current was almost complete at -40 mV. No voltage-dependent Na(+) current was found in these cells. The octopus arm muscle cells generate fast (3 ms) overshooting spikes in physiological conditions that are carried by a slowly inactivating L-type Ca(2+) current.
章鱼臂为灵活附肢的神经肌肉系统提供了一个独特的模型。我们之前报道了臂部肌肉细胞的电致密性及其丰富的可兴奋特性，范围从快速振荡到超射动作电位。在此，我们对肌肉细胞膜中的电压激活离子电流进行了表征。我们发现了三种去极化激活离子电流：1）一种高压激活的L型Ca(2+)电流，在约-35 mV时开始激活，当Ca(2+)被Mg(2+)取代时消失，被硝苯地平阻断，并表现出Ca(2+)依赖性失活。该电流具有非常快速的激活动力学（在数毫秒内达到峰值）和缓慢的失活动力学（时间常数约为50 ms）。2）一种延迟整流K(+)电流，被10 mM四乙铵（TEA）完全阻断，被10 mM 4-氨基吡啶（4AP）部分阻断。该电流表现出相对缓慢的激活动力学（时间常数约为15 ms），并且仅以约150 ms的时间常数部分失活。3）一种瞬时A 型K(+)电流，被10 mM 4AP完全阻断，被10 mM TEA部分阻断。该电流表现出非常快速的激活动力学（在数毫秒内达到峰值），并以约60 ms的时间常数失活。A 型电流在-40 mV时几乎完全失活。在这些细胞中未发现电压依赖性Na(+)电流。章鱼臂肌肉细胞在生理条件下产生快速（约3 ms）的超射尖峰，由缓慢失活的L型Ca(2+)电流传导。
