CHARACTERIZATION OF THE EFFECT OF SR48692 ON INOSITOL MONOPHOSPHATE, CYCLIC-GMP AND CYCLIC-AMP RESPONSES LINKED TO NEUROTENSIN RECEPTOR ACTIVATION IN NEURONAL AND NONNEURONAL CELLS

1 Neurotensin stimulated inositol monophosphate (IP1) formation in both human colonic carcinoma HT29 cells and in mouse neuroblastoma N1E115 cells with EC(50) values of 3.5+/-0.5 nM (n=4) and 0.46+/-0.02 nM (n=3), respectively. Neurotensin also stimulated cyclic GMP production with an EC(50) of 0.47+/-1.2 nM and inhibited cyclic AMP accumulation induced by forskolin (0.5 mu M) with an IC50 Of 1.33+/-1.5 nM (n=3) on the N1E115 cell line. 2 The competitive antagonism by the non-peptide neurotensin receptor antagonist, SR48692 of neurotensin-induced IPI formation revealed pA(2) values of 8.7+/-0.2 (n=3) for HT29 and 10.1+/-0.2 (n=3) for N1E115 cells. SR48692 also antagonized the cyclic GMP and cyclic AMP responses induced by neurotensin in the N1E115 cell line with pA(2) values of 10.7+/-0.7 (n=3) and 9.8+/-0.3 (n=3), respectively. 3 In CHO cells transfected with the rat neurotensin receptor, neurotensin stimulated IP1 and cyclic AMP formation with EC(50) values of 3.0+/-0.5 nM (n=3) and 72.2+/-20.7 nM (n=3), respectively. Both effects were antagonized by SR48692, giving pA(2) values of 8.4+/-0.1 (n=3) for IP1 and 7.2+/-0.4 (n=3) for cyclic AMP responses. 4 Radioligand binding experiments, performed with [I-125]-neurotensin (0.2 nM), yielded IC50 values of 15.3 nM (n=2) and 20.4 nM (n=2) for SR48692 versus neurotensin receptor binding sites labelled in HT29 and N1E115 cells, respectively. 5 In conclusion, SR48692 appears to be a potent, species-independent antagonist of the signal transduction events triggered by neurotensin receptor activation in both neuronal and non-neuronal cell systems.