Torkkeli P H, French A S
Department of Physiology, University of Alberta, Edmonton, Canada.
Pflugers Arch. 1994 Nov;429(1):72-8. doi: 10.1007/BF02584032.
This paper describes the first voltage-clamp recordings from an arthropod cuticular sensory neuron. In the femoral tactile spine neuron of the cockroach Periplaneta americana, a rapidly activating and inactivating outward current, IA, appeared when the neuron was hyperpolarized for a short period before a depolarizing test pulse. IA could be separated from the other outward currents using 5 mM 4-aminopyridine (4-AP), which specifically blocked it. Tetraethylammonium (TEA), (50 mM) did not remove IA, but decreased the steady-state outward current by about 50%. The threshold for IA activation was about -75 mV. The minimum activation and inactivation time constants were approximately 0.2 ms and 15 ms, respectively. The voltage dependencies of activation and inactivation were well fit-ted by Boltzmann distributions, giving values of membrane potential at half-maximal activation (V50) equal to -56.5 mV and an equivalent gating charge of n = 3.9 for activation and V50 = -86.7 mV and n = 3.4 for inactivation. In current-clamp recordings, 4-AP reversibly reduced the cell's normal adaptation by lowering the threshold for action potentials, but did not affect the amplitude or duration of single action potentials. These results indicate that IA plays a role in short-term adaptation by opposing membrane depolarization and reducing the spike frequency during maintained stimulation.
本文描述了对节肢动物表皮感觉神经元进行的首次电压钳记录。在美洲大蠊的股触觉棘神经元中，当神经元在去极化测试脉冲之前短时间超极化时，会出现一种快速激活和失活的外向电流IA。使用5 mM 4-氨基吡啶（4-AP）可将IA与其他外向电流分离，4-AP能特异性阻断IA。四乙铵（TEA，50 mM）不能消除IA，但可使稳态外向电流降低约50%。IA激活的阈值约为 -75 mV。最小激活和失活时间常数分别约为0.2 ms和15 ms。激活和失活的电压依赖性很好地符合玻尔兹曼分布，激活时半最大激活的膜电位值（V50）为 -56.5 mV，等效门控电荷n = 3.9；失活时V50 = -86.7 mV，n = 3.4。在电流钳记录中，4-AP通过降低动作电位阈值可逆地减少了细胞的正常适应性，但不影响单个动作电位的幅度或持续时间。这些结果表明，IA通过对抗膜去极化和在持续刺激期间降低动作电位频率，在短期适应性中发挥作用。
