?1 and ?2 Adrenergic receptors in mouse brain astrocytes from primary cultures

Abstract

Mouse brain astrocytes from primary cultures were found to contain both α₁ and α₂ adrenergic receptors. ³H WB 4101 labeled one category of binding site (K_D=1.5±0.39 nM, Bmax =64±7.9 fmoles/mg protein) with typical α₁ adrenergic specificity (WB 4101 >prazosin>yohimbine). The density of α₁ adrenergic receptors was 2–3 times higher in mouse cerebral cortex than in glial cells. Like rat brain [U'Pritchard et al, 1979; Rouot et al, 1980], mouse glial cells were found to contain two categories of ³H clonidine binding sites: high affinity sites, which were identical to the high but not to the low affinity sites found in rat brain, since (1) they displayed the same affinity for ³H clonidine (K_D=1.2±0.13 nM, n=4) and the same typical α₂ adrenergic specificity (yohimbine>WB 4101 > prazosin); (2) the dissociation rate constant for clonidine binding was equal to 0.06 min⁻¹, a value close to that found previously for the high affinity ³H clonidine binding sites in rat brain (0.05 min⁻¹); and (3) divalent cations augmented and guanyl nucleotides reduced ³H clonidine binding as in rat brain. Na⁺ decreased ³H clonidine binding in a complex manner. The number of high affinity sites in glial cells (52 ±9.4 fmoles/mg protein, n=4) was half the number found in mouse cerebral cortex (98 fmoles/mg protein). Low affinity ³H clonidine binding sites (K_D=81±18 nM, Bmax=96±5.8 fmoles/mg protein, n=3) were not fully characterized. In conclusion, glial cells contained the same α adrenergic receptors as those described in brain, but their physiological function is not yet known.