Study of Signal Transduction and the Mechanism of Revelation of Motility in Fish Chromatophores

鱼类色素膜上存在各种激素物质和神经递质的受体。然而，化学信使的接收和实际机械力-化学事件之间的联系仍然知之甚少。到目前为止，已经提出cAMP作为第二信使在细胞内的作用以及G蛋白参与腺苷环化酶的激活或失活。本研究表明，Ca~(2+)和1，4，5-三磷酸肌醇(IP_3)也是第二信使。也就是说，当黑素载体受到神经递质的刺激时，去甲肾上腺素(ME)，一种细胞内的钙离子水平会增加，从而触发黑素小体的聚集。此外，将IP_3应用于Brij-58渗透细胞可引起色素颗粒的聚集。IP_3可能通过与胞内钙离子储存膜上的受体结合，释放钙离子。电子显微镜观察…更多的结果表明，细胞膜下和细胞质中分别存在大量的吞噬小泡和光滑内质网。这些生物体可能是储存钙的隔间。虽然目前还不能否认Ca~(2+)通过钙通道进入生色体，但可以肯定的是，即使在无Ca~(2+)、Mg~(2+)的生理盐水中，黑素载体也是通过色素聚集反应去甲肾上腺素的。细胞内Ca~(2+)浓度的增加可能会引起钙调素的激活，这是一种典型的钙离子结合蛋白，从而导致其他酶的激活，如磷酸二酯酶。W-7对去甲肾上腺素诱导的发色团反应有明显的拮抗作用，但在50 mM时抑制作用最强(发色团反应程度约为40%)。这些结果表明，鱼类发色团、钙调素系统(IP_3)和CAPM系统中的信号转导过程同时进行。事实上，细胞膜上存在^&lt；α&gt；1-和α_2-肾上腺素能受体，尽管发现后一种亚型占主导地位(约70%)。此外，我们还发现色素的聚集需要能量，动力蛋白-微管蛋白的相互作用可能会产生迁移的动力。较少

Various receptors for hormonal substances and neurotransmitters are present on the membrane of fish chromatophores. However, the linkage between the reception of the chemical messengers and the actual mechano-chemical events has still been poorly understood. Up to now, the intracellular role of cAMP as a second messenger and the involvement of G-protein in the activation or inactivation of the adenylate cyclase have been suggested. In the present study, it was shown that Ca^<2+> and Inositol 1,4,5-trisphosphate (IP_3) are also the second messengers. That is, when the melanophores were stimulated by the neurotransmitters, norepinephrine (ME), an intracellular Ca^<2+> level was increased, which triggers an aggregation of melanosomes. In addition, the application of IP_3 to Brij 58-permeabilized cells caused the aggregation of pigment granules. Probably, IP_3 may bind to its specific receptors on the membrane of intracellular store of Ca^<2+> to release the ions. Electron microscopic obse … More rvations indicated that many pinocytotic vesicles and smooth endoplasmic reticulum are present beneath the membrane and in the cytoplasm, respectively. These organisms may be the Ca^<2+>- storing compartments. Although the influx of Ca^<2+> into the chromatophores through the calcium channels is undeniable at the present time, it was certainly confirmed that the melanophores responded to NE by the pigment aggregation even in Ca^<2+>, Mg^<2+>-free saline. The increase in cytosolic Ca^<2+> concentration may elicit the activation of calmodulin, a representative Ca^<2+>-binding protein, leading to the subsequent activation of other enzymes such as phosphodiesterase. W-7 was found to antagonize NE-induced responses of the chromatophores largely, but the inhibitory action of the drug reached the uppermost limit at the concentration of 50 muM (Degree of the chromatophore response : about 40 %).These results imply the simultaneous progress of both processes concerning the signal transduction in fish chromatophores, Ca^<2+>-calmodulin system (IP_3) and cAPM system. In fact, ^<alpha>1- and alpha_2-adrenoceptors are present on the cell membrane, although the latter subtype is found to be dominant (about 70%). Moreover, we found that the pigment aggregation requires energy, and that dynein-tubulin interaction may generate the motive force for the migration. Less