Agonist and antagonist modulation of [S-35]-GTP gamma S binding in transfected CHO cells expressing the neurotensin receptor

1 The functional interaction of the cloned rat neurotensin receptor with intracellular G-proteins was investigated by studying the binding of the radiolabelled guanylyl nucleotide analogue [S-35]-GTP gamma S induced by neurotensin to membranes prepared from transfected Chinese hamster ovary (CHO) cells. 2 The agonist-induced binding of [S-35]-GTP gamma S was only detected in the presence of NaCl in the incubation buffer. However, it was also demonstrated that the binding of [H-3]-neurotensin to its receptor was inhibited by NaCl. In the presence of 50 mM NaCl, the binding of the labelled nucleotide was about 2 fold increased by stimulation with saturating concentrations of neurotensin (EC50 value of 2.3 +/- 0.9 nM). 3 The stimulation of [S-35]-GTP gamma S binding by neurotensin was mimicked by the stable analogue of neurotensin, JMV-449 (EC50 value of 1.7 +/- 0.4 nM) and the neurotensin related peptide neuromedin N (EC50 value of 21 +/- 6 nM). 4 The NT-induced [S-35]-GTP gamma S binding was competitively inhibited by SR48692 (pA(2) value of 9.55 +/- 0.28), a non-peptide neurotensin receptor antagonist. SR48692 alone had no effect on the specific binding of [S-35]-GTP gamma S. 5 The response to neurotensin was found to be inhibited by the aminosteroid U-73122, a putative inhibitor of phospholipase C-dependent processes, indicating that this drug may act at the G-protein level. 6 Taken together, these results constitute the first characterization of the exchange of guanylyl nucleotides at the G-protein level that is induced by the neuropeptide neurotensin after binding to its receptor.