Nonnengässer C, Holland E M, Harz H, Hegemann P
Max-Planck-Institut für Biochemie, Martinsried, Germany.
Biophys J. 1996 Feb;70(2):932-8. doi: 10.1016/S0006-3495(96)79636-4.
Chlamydomonas exhibits a sequence of a photoreceptor current and two flagellar currents upon stimulation with bright green flashes. The currents are thought to be a prerequisite for the well-known photophobic responses. In the preceding paper, we analyzed the kinetics of these currents and their dependence on extracellular divalent ions. Here, we show that the photoreceptor current can be carried by monovalent ions (K+ > NH4+ > Na+), provided that the driving force is high enough. The small residual photoreceptor current observed in the absence of Ca2+ is able to evoke flagellar currents at low extracellular pH. This demonstrates that signal transduction from the rhodopsin to the flagella is not inevitably dependent on extracellular Ca2+. Double-flash experiments exclude a contribution of intra-rhodopsin charge movements to the photoreceptor current signal. Evidence will be provided for the existence of nonlocalized K+ outward currents, which counterbalance the localized Ca2+ influx and repolarize the cell after a light flash. A model is presented that explains the different pathways for direction changes and phobic responses.
衣藻在受到亮绿色闪光刺激时会表现出一系列光感受器电流和两种鞭毛电流。这些电流被认为是众所周知的避光反应的先决条件。在前一篇论文中，我们分析了这些电流的动力学及其对细胞外二价离子的依赖性。在此，我们表明，只要驱动力足够高，光感受器电流可以由单价离子携带（K+>NH4+>Na+）。在没有Ca2+的情况下观察到的小的残余光感受器电流能够在低细胞外pH值下诱发鞭毛电流。这表明从视紫红质到鞭毛的信号转导并非不可避免地依赖于细胞外Ca2+。双闪光实验排除了视紫红质内电荷移动对光感受器电流信号的贡献。将提供证据证明存在非局部化的K+外向电流，其在闪光后平衡局部Ca2+内流并使细胞复极化。提出了一个模型来解释方向变化和避光反应的不同途径。
