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Table 3 Competition of [3H] DAMGO binding among the rat MOR-1 variants

From: Identification and characterization of seven new exon 11-associated splice variants of the rat mu opioid receptor gene, OPRM1

Ligand K i Value
  rMOR-1 rMOR-1H1 rMOR-1H2 rMOR-1i1 rMOR-1i2 rMOR-1i3
Morphine 1.5 ± 0.2 2.0 ± 0.3 0.8 ± 0.1 1.3 ± 0.4 1.2 ± 0.2 1.6 ± 0.2
M6G 4.5 ± 0.3 4.5 ± 0.5 2.6 ± 0.6 3.8 ± 0.5 5.1 ± 1.0 6.3 ± 0.7
DADLE 2.4 ± 0.1   1.9 ± 0.3    
DSLET 6.3 ± 0.3   7.2 ± 1.1    
Naloxone 0.8 ± 0.1 0.9 ± 0.1 0.8 ± 0.3 0.9 ± 0.1 0.7 ± 0.1 1.3 ± 0.2
β-Endorphin 2.7 ± 0.2 3.1 ± 0.3 3.8 ± 1.9 3.3 ± 0.3 3.7 ± 0.3 6.3 ± 0.7
Dynorphin A 15.5 ± 0.9 37.5 ± 5.3 21.8 ± 5.1 16.2 ± 3.5 23.6 ± 2.8 34.6 ± 6.8
U50,488H > 500 > 500 > 500 > 500 > 500 > 500
DPDPE > 500 > 500 > 500 > 500 > 500 > 500
  1. [3H] DAMGO binding was performed in membranes of CHO cells stably expressing the indicated variants. Dissociate constants, K i values, were determined from IC50 values of at least three independent determinations. One-way ANOVA was used to compare the K i values for each drug among the variants. Of the opioids, only M6G (p = 0.0157) showed significant difference with lower K i value of rMOR-1H2 as compared to that of rMOR-1i3 (p < 0.01) in Tukey post hoc analysis.