α-肾上能受体兴奋剂及阻断剂对米虾棕色载色细胞内色素聚散的效应

萘唑啉或肾上腺素能使米虾离体棕色胞内色素集中,此作用被酚妥拉明短时所阻断。异丙肾上腺素对棕色胞无影响。作者认为棕色胞上只具有α受体,可以作为筛选α受体兴奋剂及阻断剂的模型。

EFFECTS OF ALPHA-ADRENOCEPTOR AGONIST AND ANTAGONIST ON THE BROWN CHROMATOPHORES OF A SHRIMP, CARIDINA SP.

Responses of brown chromatophores under the carapace of a shrimp, Caridina sp. to adrenergic agonist and antagonist were investigated in vitro. When the lateral portion of the carapace was placed in the medium (0.6% NaCl), the brown chromatophores lying just beneath, the carapace began to disperse and became to a full expanded (stage 5) in about 40 min. Naphazoline and adrenaline caused marked contraction of the chromatophores. Isoproterenol (a beta-adrenoceptor agonist), on the other hand, was unable to concentrate or to disperse the pigment.If the chromatophores were pre-treated with phentolamine (an alpha-adrenoceptor blocking agent) for 15 min. the response of chromatophores to naphazoline (or adrenaline) was blocked. After a pause of about 15 min or more the pigment of the chromatophores began to concentrate but at a slower rate even in the presence of phentolamine. In a mixture of phentolamine and naphazoline the former did not show any blocking effect, indicating that the phentolamine is much weaker than naphazoline in competition with their receptors. After the pigment is concentrated by naphazoline, phentolamine is more potent than saline alone to disperse the pigment of the chromatophores.The above results demonstrate clearly that alpha-adrenergic receptors are present on the surface of brown chromatophores, but no beta-receptor. It demonstrates also that the blockade of phentolamine is brief in duration.The in vitro brown chromatophores may be used as a model to screen alpha-adrenoceptor agonist and antagonist as well as to test the relative potencies between them.