Benyhe S, Varga E, Hepp J, Magyar A, Borsodi A, Wollemann M
Institute of Biochemistry, Biological Research Center of Hungarian Academy of Sciences, Szeged.
Neurochem Res. 1990 Sep;15(9):899-904. doi: 10.1007/BF00965909.
The distribution and properties of frog brain kappa-opioid receptor subtypes differ not only from those of the guinea pig brain, but also from that of the rat brain. In guinea pig cerebellum the kappa 1 is the dominant receptor subtype, frog brain contains mainly the kappa 2 subtype, and the distribution of the rat brain subtypes is intermediate between the two others. In competition experiments it has been established that ethylketocyclazocine and N-cyclopropylmethyl-norazidomorphine, which are nonselective kappa-ligands, have relatively high affinities to frog brain membranes. The kappa 2 ligands (Met5)enkephalin-Arg6-Phe7 and etorphine also show high affinities to the frog brain. Kappa 1 binding sites measured in the presence of 5 microM/D-Ala2-Leu5/enkephalin represent 25-30% of [3H]ethylketocyclazocine binding in frog brain membranes. The kappa 2 subtype in frog brain resembles more to the mu subtype than the delta subtype of opioid receptors, but it differs from the mu subtype in displaying low affinity toward beta-endorphin and /D-Ala2-(Me)Phe4-Gly5-ol/enkephalin (DAGO). From our data it is evident that the opioid receptor subtypes are already present in the amphibian brain but the differences among them are less pronounced than in mammalian brain.
蛙脑κ-阿片受体亚型的分布和特性不仅与豚鼠脑不同，也与大鼠脑不同。在豚鼠小脑中，κ1是主要的受体亚型，蛙脑主要含有κ2亚型，而大鼠脑亚型的分布介于两者之间。在竞争实验中已证实，非选择性κ配体乙基酮环唑辛和N-环丙基甲基-去甲阿齐吗啡对蛙脑膜具有较高亲和力。κ2配体（Met5）脑啡肽-Arg6-Phe7和埃托啡对蛙脑也显示出高亲和力。在5μM/D-Ala2-Leu5/脑啡肽存在下测得的κ1结合位点占蛙脑膜中[3H]乙基酮环唑辛结合的25%-30%。蛙脑中的κ2亚型与阿片受体的μ亚型比δ亚型更相似，但它与μ亚型的不同之处在于对β-内啡肽和/D-Ala2-(Me)Phe4-Gly5-ol/脑啡肽（DAGO）显示出低亲和力。从我们的数据可以明显看出，阿片受体亚型在两栖动物脑中已经存在，但它们之间的差异不如在哺乳动物脑中那么明显。
