Alpha 2-adrenergic receptors in neuronal and glial cultures: characterization and comparison.
Membranes prepared from either neuronal or glial cultures contain alpha 2-adrenergic receptors as determined by the characteristics of [3H]yohimbine [( 3H]YOH) binding. The binding was rapid, reversible, saturable, dependent on the protein concentration used, and reached equilibrium by 5 min in membranes from both neuronal and glial cultures. Scatchard analyses of saturation isotherms revealed similar KD values of 13.7 +/- 1.35 nM (n = 10) for neuronal cultures and 18.42 +/- 2.34 nM (n = 10) for glial cultures. Glial cultures contained many more binding sites for [3H]YOH than neuronal cultures, having a Bmax of 1.6 +/- 0.33 pmol/mg protein (n = 10) compared with 0.143 +/- 0.018 pmol/mg protein (n = 10) in neurons. Drugs selective for alpha 2-adrenergic receptors were the most effective displacers of [3H]YOH binding in both neuronal and glial cultures, i.e., the alpha 2-adrenergic antagonists rauwolscine and yohimbine were better displacers than the other catecholamine antagonists prazosin, corynanthine, or propranolol. The agonists showed the same pattern with the alpha 2-selective drugs clonidine and naphazoline being the most effective competitors for the [3H]YOH site. GTP and its nonhydrolyzable analog. 5'-guanylyl-imidodiphosphate, were able to lower the affinity of the alpha 2-receptors for agonists but not antagonists in membranes from both neuronal and glial cultures, suggesting that the receptors are linked to a G protein in both cell types. The presence of alpha 2-adrenergic receptors in neuronal cultures was also substantiated by light microscopic autoradiography of [3H]YOH binding. In summary, we have demonstrated that both neuronal and glial cultures contain alpha 2-adrenoceptors.
Richards
E M
EM
Department of Physiology, University of Florida College of Medicine, Gainesville 32610.
Sumners
C
C
Chou
Y C
YC
Raizada
M K
MK
Phillips
M I
MI
D000818:Animals; D001345:Autoradiography; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D005455:Fluorescent Antibody Technique; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D007700:Kinetics; D009457:Neuroglia / Q000378:metabolism* / Q000648:ultrastructure; D009474:Neurons / Q000378:metabolism* / Q000648:ultrastructure; D009994:Osmolar Concentration; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D015016:Yohimbine / Q000378:metabolism
D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D006165:Guanylyl Imidodiphosphate