STABLE EXPRESSION OF THE CLONED RAT-BRAIN NEUROTENSIN RECEPTOR INTO FIBROBLASTS - BINDING-PROPERTIES, PHOTOAFFINITY-LABELING, TRANSDUCTION MECHANISMS, AND INTERNALIZATION

The study of the pharmacological, biochemical, and transduction proper ties of the cloned rat brain neurotensin receptor was carried out in t hymidine kinase mutant fibroblasts stably transfected with the recepto r cDNA. The interaction of neurotensin with transfected fibroblasts le ads to a concentration-dependent stimulation of phosphatidylinositol h ydrolysis and intracellular calcium. These effects are totally inhibit ed by the nonpeptide neurotensin antagonist SR48692. By contrast, this receptor remains unable to modulate intracellular levels of cyclic nu cleotides. The transfected neurotensin receptor can be solubilized in an active form by digitonin with an identical pharmacological profile, whereas the detergent 3-[(3-cholamidopropyl) dimethylammonio]-1-propa ne sulfonic acid is unable to solubilize the binding activity. The bin ding of iodinated neurotensin to transfected fibroblasts bearing the c loned receptor remains partly undissociated even after an acid washing step, indicating that the transfected neurotensin receptor retains th e capacity to be internalized according to a temperature-dependent mec hanism. Indeed, the sequestration of the neurotensin-receptor complex can be blocked by phenylarsine oxide. Finally, photoaffinity labeling experiments reveal that the cloned rat brain neurotensin receptor is e xpressed under two forms with molecular masses of 50 and 60 kDa. Label ing and internalization of these two proteins are totally blocked by t he neurotensin antagonist SR48692.