Gingl Ewald, French Andrew S
Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, B3H 4H7 Canada.
J Neurosci. 2003 Jul 9;23(14):6096-101. doi: 10.1523/JNEUROSCI.23-14-06096.2003.
Rapid responses to sensory stimulation are crucial for survival. This must be especially true for mechanical stimuli containing temporal information, such as vibration. Sensory transduction occurs at the tips of relatively long sensory dendrites in many mechanoreceptors of both vertebrates and invertebrates, but little is known about the electrical properties of these crucial links between transduction and action potential generation. The VS-3 slit-sense organ of the spider Cupiennius salei contains bipolar mechanosensory neurons that allow voltage-clamp recording from the somata, whereas mechanotransduction occurs at the tips of 100- to 200-microm-long sensory dendrites. We studied the properties of VS-3 sensory dendrites using three approaches. Voltage-jump experiments measured the spread of voltage outward from the soma by observing total mechanically transduced charge recovered at the soma as a function of time after a voltage jump. Frequency-response measurements between pseudorandom mechanical stimulation and somatic membrane potential estimated the passive cable properties of the dendrite for voltage spread in the opposite direction. Both of these sets of data indicated that the dendritic cable would significantly attenuate and retard a passively propagated receptor potential. Finally, current-clamp observations of receptor potentials and action potentials indicated that action potentials normally start at the distal dendrites and propagate regeneratively to the soma, reducing the temporal delay of passive conduction.
对感觉刺激的快速反应对生存至关重要。对于包含时间信息的机械刺激（如振动）而言，情况必然更是如此。在脊椎动物和无脊椎动物的许多机械感受器中，感觉转导发生在相对较长的感觉树突末端，但对于这些转导与动作电位产生之间关键环节的电特性，我们却知之甚少。蜘蛛Cupiennius salei的VS-3裂隙感觉器官包含双极机械感觉神经元，这使得能够从细胞体进行电压钳记录，而机械转导发生在100至200微米长的感觉树突末端。我们使用三种方法研究了VS-3感觉树突的特性。电压跃变实验通过观察电压跃变后细胞体上恢复的总机械转导电荷随时间的变化，测量了电压从细胞体向外的扩散。伪随机机械刺激与细胞膜电位之间的频率响应测量估计了树突在相反方向上电压传播的被动电缆特性。这两组数据均表明，树突电缆会显著衰减并延迟被动传播的感受器电位。最后，对感受器电位和动作电位的电流钳观察表明，动作电位通常始于远端树突，并以再生方式传播至细胞体，从而减少了被动传导的时间延迟。
