CHARACTERIZATION OF THE HUMAN OXYTOCIN RECEPTOR STABLY EXPRESSED IN 293 HUMAN EMBRYONIC KIDNEY-CELLS

The human oxytocin (OT) receptor was stably expressed in 293 embryonic kidney cells (293/OTR), characterized pharmacologically and compared to human uterine myometrial receptors. The cloned receptor is expresse d at a reasonably high density (0.82 fmole/mu g protein) and exhibits high affinity for [H-3]OT (K-d=0.32 nM), similar to the value found in human myometrial tissue. The rank-order of potency for various antago nist and agonist ligands from several structural classes is also simil ar between the cloned and native receptor, as seen in a comparison of their inhibitory constants for [3H]OT binding. Agonist affinity at the cloned OT receptor is decreased by guanine nucleotide analogs, demons trating functional G-protein-coupling. The OT receptor in 293 cells, l ike in human myometrium, is also coupled to the inositol phosphate pat hway. In 293/OTR cells, OT stimulates inositol phosphate accumulation with an EC(50)=4.1 nM, an effect blocked by a potent and selective OT antagonist, L-366,948. Additionally, the cloned receptor in 293 cells desensitizes to high concentrations of OT, similar to the desensitizat ion in myometrial tissue and also described for several other G-protei n-coupled receptors. These results illustrate the utility of the 293 c ell line for expressing human OT receptors in an environment quite com parable to the native myometrial tissue.