Oliver Dominik, Brinkmann Martin, Sieger Thiemo, Thurm Ulrich
Institute for Neurobiology and Behavioral Biology, University of Münster, Badestr. 9, D-48149 Münster, Germany.
J Exp Biol. 2008 Sep;211(Pt 17):2876-88. doi: 10.1242/jeb.018515.
Nematocytes, the stinging cells of Hydrozoa, can be considered as prototypic mechanosensory hair cells bearing a concentric hair bundle, the cnidocil apparatus. These cells produce typical mechanoreceptor potentials in response to deflection of their cnidocil. Here we show that mechanosensory signals are relayed to neighbouring nematocytes via chemical neurotransmission and that nematocytes receive synaptic input from surrounding nematocytes, hair cells and probably from epithelial cells. Intracellular voltage recordings from stenotele nematocytes of capitate hydroid polyps showed two distinct types of responses when other nematocytes within the same tentacle were mechanically stimulated: (i) graded depolarizations of variable duration ('L-potentials'), and (ii) uniform impulse-like, often repetitive depolarizations ('T-potentials') that occurred in correlation with contractions of epitheliomuscular cells. Voltage clamp experiments showed that despite the stereotyped time course of T-potentials, their generation did not involve electrically excitable conductances. Instead, time course, post-stimulus delay, susceptibility to blockers of neurotransmission and gap junctions, and induction by electrical stimulation of other nematocytes indicate that L- and T-potentials are postsynaptic, most likely glutamatergic potentials. Both result from different presynaptic pathways: L-potentials are induced monosynaptically by presynaptic receptor potentials, T-potentials are most likely triggered by presynaptic action potentials propagating through the ectodermal epithelium via gap junctions. Moreover, contact-chemosensory (phospholipid) stimulation of the presynaptic nematocyte is a positive modulator of the nematocyte's afferent synaptic efficacy and of cnidocyst discharge, both triggered by mechanoreceptor potentials. The results reveal that hydrozoan nematocytes act as bimodal sensory cells, signalling coincident chemical and mechanical stimuli indicative of prey, and receive signals from other nematocytes and sensory cells.
刺细胞是水螅虫纲的刺细胞，可以被认为是具有同心毛束（刺丝囊装置）的原型机械感觉毛细胞。这些细胞在其刺丝囊受到偏转时会产生典型的机械感受器电位。在这里，我们表明机械感觉信号通过化学神经传递传递给相邻的刺细胞，并且刺细胞从周围的刺细胞、毛细胞以及可能从上皮细胞接收突触输入。对头状水螅虫息肉的刺丝囊刺细胞进行细胞内电压记录显示，当同一触手内的其他刺细胞受到机械刺激时，会出现两种不同类型的反应：（i）持续时间可变的分级去极化（“L电位”），以及（ii）与上皮肌细胞收缩相关的均匀脉冲样、通常重复的去极化（“T电位”）。电压钳实验表明，尽管T电位具有刻板的时间进程，但其产生并不涉及电兴奋性电导。相反，时间进程、刺激后延迟、对神经传递和间隙连接阻滞剂的敏感性以及对其他刺细胞电刺激的诱导表明，L电位和T电位是突触后电位，最有可能是谷氨酸能电位。两者都来自不同的突触前途径：L电位由突触前感受器电位单突触诱导，T电位最有可能由通过间隙连接在外胚层上皮中传播的突触前动作电位触发。此外，对突触前刺细胞的接触化学感觉（磷脂）刺激是刺细胞传入突触效能和刺丝囊放电的正调节因子，两者均由机械感受器电位触发。结果表明，水螅虫纲的刺细胞作为双峰感觉细胞，发出指示猎物的同时存在的化学和机械刺激信号，并从其他刺细胞和感觉细胞接收信号。
