Sea urchins can detect and respond to light, and many species of sea urchins are negatively phototaxic. Light detection is hypothesized to occur via photoreceptors located on sea urchin tube feet, and opsins have been detected in tube feet, spines, and the test. However, the molecular mechanisms underlying light detection are, for the most part, unknown. Individual tube feet disc cells were isolated from purple sea urchins (Strongylocentrotus purpuratus), and the electrical responses of these cells to varying levels of illumination were quantified using the patch clamp technique. No currents were observed under bright illumination, whereas under dark conditions, large, slowly activating currents were consistently observed. Two types of cells were functionally identified based on their responses to darkness. Type I cells sustained currents indefinitely in the dark, whereas Type II cell currents spontaneously decayed after several seconds. The large currents observed were composed of the summation of many smaller events that were characterized by a rapid onset and an exponentially decaying component, which may be indicative of direct vesicular release from the tube feet disc cells in response to the dark conditions.

中文翻译：

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海胆管足细胞中依赖光的电活动

海胆可以探测和响应光，许多种类的海胆具有负趋光性。光检测被假设是通过位于海胆管脚上的光感受器发生的，并且在管脚、刺和测试中已经检测到视蛋白。然而，光检测的分子机制在很大程度上是未知的。从紫色海胆 (Strongylocentrotus purpuratus) 中分离出单个管足盘细胞，并使用膜片钳技术量化这些细胞对不同光照水平的电响应。在明亮的照明下没有观察到电流，而在黑暗条件下，持续观察到大的、缓慢激活的电流。根据它们对黑暗的反应，在功能上鉴定了两种类型的细胞。I 型细胞在黑暗中无限期地持续电流，而 II 型细胞电流在几秒钟后自发衰减。观察到的大电流由许多较小事件的总和组成，这些事件的特征是快速发生和指数衰减成分，这可能表明管足盘细胞响应黑暗条件直接释放囊泡。