Identification and characterization of substance P receptors on LRM55 glial cells

Substance P (SP) receptors were described by the specific binding of [3H]SP to several neuronal and glial cell lines. The neuronal cell lines N18 and NG108-15 were found to contain few if any SP receptors (less than 5 fmol/mg of protein). The glial cell line LRM55 contained large numbers (Bmax = 707 fmol/mg of protein) of a single class of SP binding sites (Kd = 276 pM). [3H]SP binding could be inhibited by a number of c-terminal SP fragments and the tachykinins physalaemin, eledoisin and kassinin. The binding kinetics and pharmacology of these receptors are similar to those the authors have previously described in the brain. Activation of SP receptors was shown to inhibit cyclic AMP-dependent, beta adrenergic-stimulated taurine release from LRM55 glial cells. SP inhibition must occur by mechanisms affecting taurine release after adenylate cyclase activation, inasmuch as SP has no significant effect on beta adrenergic-stimulated increases or basal levels of intracellular cyclic AMP.