Neurotensin and its analogs-Correlation of specific binding with stimulation of cyclic GMP formation in neuroblastoma clone N1E-115

The receptors which mediate neurotensin-stimulated intracellular cyclic GMP formation in murine neuroblastoma clone N1E-115 [J. A. Gilbert and E. Richelson, Eur. J. Pharmac. 99, 245 (1984)] were further characterized. The binding of [³H]neurotensin to intact N1E-115 cells at 0° displayed specificity, saturability, reversibility, and tissue linearity. A single class of neurotensin receptors was demonstrated with an apparent K_D of 9-11 nM and a B_max of 180-250 fmoles/10⁶ cells, determined by the type of serum employed in the cellular culture medium. A number of neurotensin analogs and fragments were compared for their ability to inhibit [³H]neurotensin binding and stimulate intracellular cyclic GMP formation with intact N1E-115 cells. A direct correlation was found to exist between the K_D and EC₅₀ for each peptide. The carboxyl-terminal portion of neurotensin proved to be responsible for the binding and biochemical activities of this peptide with clone N1E-115. Neurotensin(8-13) was, in fact, fifty times more potent than native neurotensin in stimulating intracellular cyclic GMP formation and had an 18-fold higher affinity for the neurotensin receptor on this neuronal cell type.