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

各种激素物质和神经递质的受体存在于鱼色素细胞的膜上。然而，化学信使的接收和实际的机械化学事件之间的联系仍然知之甚少。到目前为止，cAMP作为第二信使的细胞内作用和G蛋白参与腺苷酸环化酶的激活或失活已被提出。本研究还发现Ca^<2+>和三磷酸肌醇（IP_3）也是第二信使。也就是说，当黑素细胞受到神经递质去甲肾上腺素（NE）的刺激时，细胞内的Ca^2+水平会升高，从而引发黑素体的聚集。此外，IP_3对Brij 58透性化细胞的应用引起了色素颗粒的聚集。IP_3可能与细胞内Ca^<2+>贮存膜上的特异性受体结合而释放出Ca^<2+。电子显微镜观察 ...更多信息 实验结果表明，在胞膜下和胞质内分别存在大量的胞饮小泡和滑面内质网。这些生物体可能是Ca^2+储存区。虽然目前Ca^<2+>通过钙通道内流到色素细胞中是不可否认的，但可以肯定的是，即使在不含Ca^<2+>、Mg^<2+>的盐水中，黑色素细胞也会通过色素聚集来响应NE。胞浆Ca^2+浓度的增加可能引起钙调蛋白（一种典型的Ca^2+结合蛋白）的激活，从而导致随后其他酶（如磷酸二酯酶）的激活。结果表明，W-7对NE诱导的色素细胞反应有明显的拮抗作用，但在50 μ M时抑制作用达到最大值（色素细胞反应程度约为40%），这表明鱼类色素细胞中的信号转导过程，即Ca^2+-钙调素系统（IP_3）和cAPM系统是同时进行的。事实上，<alpha>细胞膜上存在α_1和α_2肾上腺素受体，尽管后者亚型被发现占优势（约70%）。此外，我们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产生迁移的动力。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