Characterization of serotonin-1B receptors negatively coupled to adenylate cyclase in OK cells, a renal epithelial cell line from the opossum.

We have previously reported the presence of a 5-HT1 (serotonin)-like receptor coupled in an inhibitory manner to adenylate cyclase in the opossum kidney cell line, which is derived from the kidney of a North American opossum. Pharmacological data from binding and cyclic AMP production studies indicate that this receptor does not have characteristics of a 5-HT1A, 5-HT1C or 5-HT1D receptor, but is similar to 5-HT1B receptors found in rodent tissues. Many serotonergic drugs, including 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyrindinyl)1H-indol, 5-HT and methysergide, but not (+/-)-8-hydroxy-2-(di-N-propylamino)tetralin hydrobromide or buspirone, were full agonists at this receptor as defined by the inhibition of bovine parathyroid hormone peptide fragment 1-34-stimulated cyclic AMP production in an intact cell assay. Several classical beta adrenergic antagonists including propranolol and cyanopindolol were also full agonists at this receptor. Radioligand binding studies using [125I](-)-iodocyanopindolol gave a Bmax of 88 fmol/mg of protein and a KD of 47 pM for saturation experiments carried out in the presence of GTP. In the absence of GTP, the binding data were significantly better fit by a two-site model with KD values of 10 and 345 pM. Inhibition binding experiments were consistent with the results of the cyclic AMP experiments. The identification of 5-HT1B receptors in a tissue derived from the opossum kidney suggests that these receptors may be distributed more widely than previously thought, inasmuch as other studies have found them only in neuronal tissues of rodents.(ABSTRACT TRUNCATED AT 250 WORDS)