Beta-receptor-stimulated and cyclic adenosine 3',5'-monophosphate-mediated taurine release from LRM55 glial cells

Abstract

Adrenergic stimulation of LRM55 glial cells results in the release of the neuroactive amino acid taurine. The present study characterizes the receptors involved in taurine release and shows that taurine release is mediated by cyclic adenosine 3',5'-monophosphate (cAMP). beta-Receptors in LRM55 cells were first characterized by [125I]iodohydroxybenzylpindolol binding. Binding was stereospecific and saturable with time and ligand concentration. Kinetic analysis of equilibrium binding at 37 degrees C revealed a single component of high affinity (Km = 113 pm; Bmax = 52.1 +/- 5.0 fmol/mg of protein). The pharmacologies of the stimulation of cAMP accumulation and taurine release were similar. The agonists isoproterenol (IPR), epinephrine (E) and norepinephrine (NE) showed a rank order of potency characteristic of a beta-adrenergic system (IPR greater than E greater than or equal to NE). The beta-antagonists alprenolol and propranolol inhibited the IPR stimulation of both processes; the alpha-antagonist phentolamine did not. The dependence of taurine release on cAMP was further suggested by the similarity of the two time courses and was demonstrated by the stimulation of taurine release by the cAMP analogue dibutyryl cAMP. Thus, one physiological response of glial cells to beta-adrenergic stimulation is the release of taurine. Receptor-activated release of taurine from glia represents a previously undescribed neuronal-glial interaction by which glia may actively regulate neuronal excitability.