Characterization of 5-HT 1A receptor functional coupling in cells expressing the human 5-HT 1A receptor as assessed with the cytosensor microphysiometer

Abstract

The functional activity of a series of 5-HT 1A receptor ligands has been evaluated in a cell line expressing the human 5-HT 1A receptor (h5-HT 1A · CHO) using the agonist-stimulated increase in extracellular acidification rate, measured with the microphysiometer, as a functional assay. Both 5-CT and 8-OH-DPAT were potent agonists in stimulating an increase in extracellular acidification rate in h5-HT 1A · CHO cells with estimated EC 50 values of 1.2 and 7.8 nM, respectively. Additionally, these two 5-HT 1A receptor agonists elicited a similar maximum response. Concentration-dependent agonist activity was also observed in the presence of buspirone, ipsapirone, BMY7378, NAN-190 and WAY100135, and each of these compounds behaved as partial 5-HT 1A receptor agonists. The selective 5-HT 1A receptor antagonist WAY100635 produced a potent (IC 50, 2.3 nM) and complete block of the 8-OH-DPAT-stimulated response. An evaluation of the inhibitory activity of a series of 5-HT 1A receptor antagonists produced the following rank order of potency; WAY100635 > LY206130 (IC 50, 7.1 nM) > WAY100135 (30.8 nM) > pindolol (76.2 nM) > (−)UH-301 (92.8 nM). Parallel studies on the inhibition of forskolin-stimulated adenylyl cyclase activity in h5-HT 1A · CHO cells revealed that agonist potencies were generally similar between the two functional assays and were in good agreement with the estimated 5-HT 1A receptor binding affinities. However, the relative efficacies determined for the partial agonists in the cAMP assay were substantially greater than those observed with the microphysiometer. Finally, antagonists were considerably weaker in the cAMP assay compared with the microphysiometer. The evaluation of 5-HT 1A ligands using the microphysiometer, which represents a very distinct indice of 5-HT 1A receptor function compared with the cAMP assay, results in a different profile of functional activity.