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KMID : 0377619940590090695
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Korean Jungang Medical Journal
1994 Volume.59 No. 9 p.695 ~ p.705
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Effects of Na ion and GTP-?S on the Kappa Opioid Binding
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Chang Young Chul/정영철
Chang Jin Ho/Eun Hong Bai/장진호/은홍배
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Abstract
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Three major types of opioid receptors, and, are generally recognized to exist. Owing to advance of methodology and development of more selective ligands, the concept of multiplicity of opioid receptors has been enlarged. Using a paradigm to block m and d sites with specific cold ligands, [3H} diprenorphine(DIP) labels sites. In this study, the influences of Na ion and GTP?S on the [3 H] DIP binding at sites in rat and guinea pig were examined. Diprenorphine and ethylketocyclazocine (EKC) inhibited the [3H] DIP binding more effectively in guinea pig cortex than in the rat. This shows that there are binding sites in rat and guinea pig cortices possess characteristics of 1 and 2-opioid receptor, respectively. And, U69593, a selective agonist for K-site, inhibited [3H] DIP binding in guinea pig with higher affinity and binding capacity that in rat cortex. In the presence of GTPS(50 M), Ki values of EKC and U69593 were significantly increased without change of ?max in guinea pig. In the presence of 125 mM Na ion, Ki values and Bmaxs of EKC and U69593 in guinea pig, .and of EKC in rat were significantly increased. However, the competition of U69593 could not be detected in the rat.
In the presence of both Na ion(125 mM) and GTP?S, the Ki values, not Bmaxs, of EKC and U69593 were further increased in guinea pig. But, the Ki value and Bmax of EKC were not potentiated. These data suggest that [3 H] DIP binding to ? 1 and ?2 sites is sensitive to Na ion. And, ?1 site is sensitive to GTP but ?2 site is not. However, it should be noted that the significance of these characteristics with regard to the effect of ? opioids on functional systems remains to be determined.
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KEYWORD
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