Effects of tandospirone, a novel anxiolytic agent, on human 5-HT 1A receptors expressed in Chinese hamster ovary cells (CHO cells)

Tandospirone is a novel anxiolytic agent which selectively binds to 5-HT 1A receptors. In this study, we established a stable CHO cell line expressing human 5-HT 1A receptors and examined the action of tandospirone in this cell line. The human 5-HT 1A receptor gene was transfected into CHO cells. Several clones showed specific binding of [ 3 H]8-OH-DPAT and one (5HT1A/CHO-No.5) with high density of 5-HT 1A receptors was isolated. Scatchard analysis revealed the dissociation constant (Kd) for [ 3 H]8-OH-DPAT of 2.8 nM and the expression level (Bmax) of 956 fmol/mg protein. Competition experiments of [ 3 H]8-OH-DPAT binding showed that affinities (Ki) of several compounds to human 5-HT 1A receptors were as follows; 5-HT (8.8 nM), 8-OH-DPAT (3.9 nM), tandospirone (72 nM) buspirone (32 nM), WAY-100635 (0.22 nM) and ritanserin (IC50 > 1 μ M). 5-HT, 8-OH-DPAT and tandospirone (0.1 nM–10 μ M) concentration-dependently stimulated [ 35 S]GTP γ S binding in 5-HT 1A /CHO-No.5 cells, but WAY-100635 (10 nM–10 μ M) did not. Furthermore, treatment with 5-HT, 8-OH-DPAT, tandospirone and buspirone (0.1 nM–10 μ M), but not WAY-100635 (10 nM–10 μ M), inhibited forskolin-induced cAMP production in a concentration-dependent manner. These findings suggest that 5-HT 1A /CHO-No.5 cells retain 5-HT 1A receptor and Gi/o-protein coupling and that tandospirone acts as an agonist at human 5-HT 1A receptors.