Characterization of receptors for substance P in human astrocytoma cells: radioligand binding and inositol phosphate formation.
UC11 cells, derived from a human astrocytoma, have a high density of functional substance P receptors. Radioligand binding studies were conducted with the highly selective neurokinin-1 receptor ligand [3H][Sar9,Met(O2)11]-substance P. Kinetic binding experiments conducted at 4 degrees C yielded an association rate constant k1 of 1.86 x 10(7) M-1 min-1, a dissociation rate constant k-1 of 0.00478 min-1, and a calculated kinetic KD of 257 pM. Saturation binding experiments yielded average values of KD = 447 +/- 103 pM, Bmax = 862 +/- 93 fmol/mg of protein. This Bmax corresponds to more than 150,000 binding sites/cell. Competition binding experiments with unlabeled [Sar9,Met(O2)11]-substance P yielded average values of KD = 491 +/- 48 pM and Bmax = 912 +/- 67 fmol/mg of protein. In [3H]inositol-labeled cells, substance P induced a robust inositol phosphate formation. Inositol trisphosphate levels increased as much as 20-fold within approximately 15 s of addition of substance P. This inositol trisphosphate formation was transient and had returned to baseline within the first 60-120 s. Inositol monophosphate formation, however, was linear for at least 2 h. Structure activity data on binding and inositol monophosphate formation confirmed the presence of a neurokinin-1 receptor subtype in these cells. Thus, the UC11 cell should be a useful model cell for delineating the physiological role of substance P receptors in astrocytes.
Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, Ohio.
C L
CL
Johnson
C G
CG
Johnson
D001254:Astrocytoma / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D007295:Inositol Phosphates / Q000096:biosynthesis*; D008024:Ligands; D011869:Radioligand Assay; D018040:Receptors, Neurokinin-1; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D013373:Substance P / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D007295:Inositol Phosphates; D008024:Ligands; D018040:Receptors, Neurokinin-1; D017981:Receptors, Neurotransmitter; C062618:substance P, Sar(9)-Met(O2)(11)-; D013373:Substance P