Abstract
Receptor binding of [3H]neurotensin was examined on membrane preparations derived from neuroblastoma X glioma NG108–15 hybrid cells. The specific binding was saturable and reversible, and a dissociation constant (Kd) was calculated to be about 0.24 nM from the rate constants. Scatchard analysis of neurotensin binding at equilibrium revealed a single class of binding sites with a Kd of 0.86 nM and a maximal binding capacity (Bmax) of 250 fmol/mg of protein (7700 receptor sites/cell). [D-Arg9]-Neurotensin had a high affinity (IC50 = 0.5 nM) for the neurotensin receptors, but [D-Phe11]-neurotensin had a lower affinity (IC50 = 280 nM), while angiotensin II and bradykinin had almost no affinity for [3H]neurotensin-binding sites. Under similar conditions [3H]neurotensin binding to mouse and rat brain synaptosomal fractions showed two binding sites with high (0.86 and 0.44 nM) and low (13 and 19 nM) affinities. We have examined several possible physiological consequences of neurotensin receptor binding. Neurotensin (10 microM) exhibited no influence on adenylate cyclase activity, 45Ca uptake, or 32Pi incorporation into phosphatidylinositol fractions of NG108–15 cells. Electrophysiological study of isolated NG108–15 cells revealed neurotensin-induced transient hyperpolarization followed by sustained depolarization with enhanced membrane excitability. Application of neurotensin to NG108–15 cells that had formed synapses with cultured striated muscle cells caused a considerable increase in frequency of miniature endplate potentials from the muscle cells. These data show that NG108–15 cells possess a single class of neurotensin receptors similar to a high affinity site of synaptosomal membranes from the murine brains.(ABSTRACT TRUNCATED AT 250 WORDS)