Mechanism of Signal Transduction in the Chromatophore Membrane

膜磷脂酰肌醇1，4，5-二磷酸（PIP_2）被磷脂酶C水解生成肌醇1，4，5-三磷酸（IP_3），IP_3又作用于细胞内Ca^2+储存区上的IP_3受体，释放出Ca ^2+。本研究首次在色素细胞系统中发现了该序列。通过改造一个商业化的工业显微镜系统，我们发明了一种能够同时测量色素细胞反应和细胞内Ca^2+浓度的装置。通过将其应用于培养的罗非鱼黑素细胞，去甲肾上腺素刺激后，Ca^2+迅速增加，随后黑素小体聚集。IP_3系统的参与表明，α_1-肾上腺素能受体参与了色素细胞的色素聚集。在实践中，α_1和α_2系统都可能在鱼类色素细胞中起作用，并且它们的发生率在物种之间以及在特定物种的组织之间可能不同。还认为α_2系统参与的是相对缓慢的色素运动，而α_1系统参与的是IP_3的变化，参与的是更快的反应成分。在鲶科鲶鱼中，响应交感神经刺激的色素聚集由毒蕈碱型乙酰胆碱受体介导。在半透明玻璃鲶鱼的工作中，我们表征了M3型受体。对虹膜细胞的研究也取得了重要进展。其中，对暗潜虾虎鱼树突状虹彩体反射颜色变化的研究是一个新的方面。

The concept that membranous phosphatidyl-inositol 1, 4, 5-bisphosphate (PIP_2) is hydrolyzed by phospholipase C to produce inositol 1, 4, 5-trisphosphate (IP_3), which in turn acts on IP_3 receptors on the intracellular Ca^<2+> storage compartment to release the ions has been demonstrated in a few effector cells. In this profect, the sequence has firstly been shown in the chromatophore system. The apparatus which enables us to measure the chromatophore responses and the intracellular Ca^<2+> concentration at the same time was invented by remodelling a commercial industrial microscope system. By applying this to a tilapia melanophore in culture, a quick Ca^<2+> increase followed by melanosome aggregation was demonstrated in response to norepinephrine stimulation. The present results showing the involvement of the IP_3 system strongly suggest that alpha_1-adrenergic receptors are involved in the pigment aggregation in the chromatophores. In practice, both alpha_1 and alpha_2 systems may be operating in fish chromatophores, and the ratios of their incidences may vary among species and also among tissues in a particular species. It is also assumed that alpha_2 system which involves cyclic AMP takes part in relatively slow movement of pigment, whereas alpha_1 system with the IP_3 changes has role in more rapid component of the response. In silurid catfishes, the pigment aggregation in response to sympathetic stimulation is mediated by acetylcholine receptors of the muscarinic type. Working on the translucent glass catfish, we characterized the receptors to be of the M3 type. Significant progresses have also been made withthe studies on motile iridophores. Among them, is a novel aspect on the change of reflective color from dendritic iridophores of the dark sleeper goby.