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. 1999 Oct;128(3):613-20.
doi: 10.1038/sj.bjp.0702849.

Receptor density as a factor governing the efficacy of the dopamine D4 receptor ligands, L-745,870 and U-101958 at human recombinant D4.4 receptors expressed in CHO cells

L Gazi  1 , I Bobirnac, M Danzeisen, E Schüpbach, D Langenegger, B Sommer, D Hoyer, M Tricklebank, P Schoeffter
Affiliations

Receptor density as a factor governing the efficacy of the dopamine D4 receptor ligands, L-745,870 and U-101958 at human recombinant D4.4 receptors expressed in CHO cells

L Gazi et al. Br J Pharmacol. 1999 Oct.

Abstract

1. The relationships between the density of dopamine D4.4 receptors and the agonist efficacies of L-745,870 (3-(4-[4-chlorophhenyl]piperazin-1-yl)-methyl-1H-pyrrolo [2, 3-b]pyridine) and U-101958 ((1-benzyl-piperidin-4-yl)-(3-isopropoxy-pyridin-2-yl)-methyl-a min e) were investigated in Chinese hamster ovary (CHO) cells, after treatment with the gene expression enhancer, sodium butyrate. 2. In CHO cells expressing D4.4 receptors (CHO/D4 cells), dopamine inhibited forskolin-stimulated cyclic AMP accumulation (Emax 56+/-1% inhibition, pEC50 7.4+/-0.1, n=10). U-101958 behaved as a partial agonist (39+/-7% the efficacy of dopamine, pEC50 8.1+/-0.3, n=4), whereas L-745,870 had no detectable agonist effect. 3. Receptor density, as estimated by [3H]-spiperone saturation binding was 240+/-30 fmol mg-1 protein (n=8) in CHO/D4 cell homogenates. It reached 560+/-150 (n=6), 1000+/-190 (n=4) and 840+/-120 (n=4) fmol mg-1 protein after treatment with sodium butyrate (5 mM) for 6, 18 and 48 h, respectively. 4. The increase in receptor density was associated with a gradual enhancement of the agonist effects (increased Emax and pEC50 values) of dopamine. The efficacy of U-101958 (relative to dopamine) doubled and L-745,870 was turned into a partial agonist (efficacy 49% relative to dopamine, pEC50 8. 6+/-0.2, n=6, after 48 h treatment with sodium butyrate). These agonist effects of U-101958 and L-745,870 could be antagonized by spiperone (0.1 microM) but not by raclopride (10 microM). 5. The results show that U-101958 and L-745,870 are partial agonists at human dopamine D4.4 receptors expressed in CHO cells. Their efficacy is governed by receptor density. Agonist effects of these two compounds in vivo cannot be excluded under circumstances of increased receptor levels.

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Figures

Figure 1
Figure 1
Concentration-response curves of dopamine, U-101958 and L-745,870 for inhibition of forskolin-stimulated cyclic AMP accumulation in (a) untreated CHO/D4 cells and CHO/D4 cells treated with 5 mM sodium butyrate for (b) 6 h, (c) 18 h and (d) 48 h. Data are means and vertical lines show s.e.mean from the number (n) of experiments indicated in Table 1.
Figure 2
Figure 2
Concentration-response curves of dopamine for inhibition of forskolin-stimulated cyclic AMP accumulation in CHO/D4 cells, in the absence and in the presence of (a) spiperone (0.1 μM), (b) clozapine (1 μM), (c) L-745,870 (0.1 μM), (d) U-101958 (0.1 μM) and (e) raclopride (10 μM). Data are means and vertical lines show s.e.mean from three experiments.
Figure 3
Figure 3
Concentration-response curves of (a,c) U-101958 and (b,d) L-745,870 for inhibition of forskolin-stimulated cyclic AMP accumulation in the absence and in the presence of (a,b) spiperone (0.1 μM) and (c,d) raclopride (10 μM) in CHO/D4 cells treated with 5 mM sodium butyrate for 48 h. Data are means and vertical lines show s.e.mean from three or four experiments.
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