Blackwell Publishing Journal Backfiles 1879-2005
Abstract: 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°C yielded an association rate constant k1 of 1.86 X 107M–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 ∼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.
Type of Medium: