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Table 2 Competition affinities for different opioid receptors and ligands.

From: In Vivo Regulation of the μ Opioid Receptor: Role of the Endogenous Opioid Agents

Receptor

Ligand

K (mean ± SEM) (nmol/L)

% Displacement

dre-µ

Met-ENK

684 ± 15

73.97 ± 1.29

 

Leu-ENK

1,317 ± 166

58.51 ± 2.68

 

β-END

186 ± 25

88.45 ± 2.03

 

MEGY

204 ± 53

78.98 ± 3.73

 

(d-Ala2)-MEGY

744 ± 27

66.72 ± 0.81

 

(d-Ala2, Val5)-MEGY

3,645 ± 621

43.16 ± 3.39

 

Morphine

187 ± 94

100

 

Naloxone

10.65 ± 1.53

100

  

Ki (nmol/L)

Reference

dre-δ1

β-END

36.6

29

 

MEGY

427

21

 

Morphine

22

29

dre-δ2

Met-ENK

45

30

 

Leu-ENK

175

 

MEGY

146

21

 

Morphine

1,400

30

rn-µa

Met-ENK

1.80

5

 

Leu-ENK

6.19

 

MERF

0.37

 

Morphine

7.48

rn-δb

Met-ENK

0.45

 

Leu-ENK

0.37

 

MERF

0.57

 

Morphine

302

tg-µc

Met-ENK

70.7

32

 

Leu-ENK

117

 

β-END

55.9

tg-δc

Met-ENK

24.9

 

Leu-ENK

198

 

β-END

284

  1. This table summarizes the results obtained in competition binding assays (Ki and % displacement) using (3H)-diprenorphine on membrane homogenates from HEK293 cells that stably express the µ opioid receptor from zebrafish. The results of other competition binding studies for the zebrafish δ opioid receptors dre-δ1 and dre-δ2, prototypical mammalian δ and µ receptors rn-oprm1 (rn, Rattus norvegicus (rat)) and rn-oprm1 and the amphibian µ and δ receptors tg-oprm1 and tg-oprd1 (tg, Taricha granulosa (newt)) have also been included for comparison.
  2. aIn this case, the radioligand used was the µ-selective peptidic analog (3H)-DAMGO and not (3H)-diprenorphine.
  3. bIn this case, the radioligand used was the δ-selective peptidic analog (3H)-DPDPE and not (3H)-diprenorphine.
  4. cIn this case, the radioligand used was the nonspecific antagonist (3H)-naloxone and not (3H)-diprenorphine.