TY - JOUR
T1 - Distinct specificity for corticosteroid binding sites in amphibian cytosol, neuronal membranes, plasma
AU - Orchinik, Miles
AU - Matthews, Laura
AU - Gasser, Paul J.
N1 - Funding Information:
We thank Dr. Robert Spencer for adrenalectomized rat hippocampus, Shawn Barnes for technical support, and Drs. Creagh Breuner and David Jennings for insightful discussions. This work was supported by a grant from the National Science Foundation (IBN 9604200).
PY - 2000/5
Y1 - 2000/5
N2 - To address mechanisms of corticosteroid action, one needs tools for distinguishing between the major classes of corticosteroid binding sites: neuronal membrane-associated receptors, intracellular ligand-activated transcription factors, and corticosteroid binding globulins (CBG) in plasma. We characterized the binding parameters for three classes of binding sites in an amphibian, Ambystoma tigrinum, and found that each class had a distinct pharmacological specificity. Equilibrium saturation and kinetic experiments indicated that [3H]corticosterone binds to neuronal membranes with high affinity (K(d) ≃ 0.37 nM). Aldosterone and two synthetic ligands for mammalian intracellular receptors, dexamethasone and RU486, displayed low affinity for brain membrane sites. In cytosol prepared from brain and liver, [3H]corticosterone bound to a single class of receptors with high affinity (K(d) ≃ 0.75 and 4.69 nM, respectively) and the rank order potencies for steroid inhibition of [3H]corticosterone binding was RU486 > dexamethasone ≃ corticosterone > aldosterone. In kidney and skin cytosol, [3H]corticosterone binding was best fit with a model having a high-affinity and a lower-affinity site; these sites are not consistent with the pharmacology of mammalian Type I (MR) and Type II (GR) receptors. [3H]Corticosterone also bound to presumed CBG in plasma with high affinity (K(d) ≃ 2.7 nM), but dexamethasone and androgens bound to plasma CBG with equivalently high affinity. These data demonstrate that pharmacological specificity can be a useful tool for distinguishing corticosteroid binding to different classes of binding sites. These data also indicate that there may be marked species differences in the specificity of corticosteroid binding sites. (C) 2000 Academic Press.
AB - To address mechanisms of corticosteroid action, one needs tools for distinguishing between the major classes of corticosteroid binding sites: neuronal membrane-associated receptors, intracellular ligand-activated transcription factors, and corticosteroid binding globulins (CBG) in plasma. We characterized the binding parameters for three classes of binding sites in an amphibian, Ambystoma tigrinum, and found that each class had a distinct pharmacological specificity. Equilibrium saturation and kinetic experiments indicated that [3H]corticosterone binds to neuronal membranes with high affinity (K(d) ≃ 0.37 nM). Aldosterone and two synthetic ligands for mammalian intracellular receptors, dexamethasone and RU486, displayed low affinity for brain membrane sites. In cytosol prepared from brain and liver, [3H]corticosterone bound to a single class of receptors with high affinity (K(d) ≃ 0.75 and 4.69 nM, respectively) and the rank order potencies for steroid inhibition of [3H]corticosterone binding was RU486 > dexamethasone ≃ corticosterone > aldosterone. In kidney and skin cytosol, [3H]corticosterone binding was best fit with a model having a high-affinity and a lower-affinity site; these sites are not consistent with the pharmacology of mammalian Type I (MR) and Type II (GR) receptors. [3H]Corticosterone also bound to presumed CBG in plasma with high affinity (K(d) ≃ 2.7 nM), but dexamethasone and androgens bound to plasma CBG with equivalently high affinity. These data demonstrate that pharmacological specificity can be a useful tool for distinguishing corticosteroid binding to different classes of binding sites. These data also indicate that there may be marked species differences in the specificity of corticosteroid binding sites. (C) 2000 Academic Press.
KW - Corticosteroid binding globulin
KW - Glucocorticoid receptor
KW - Mineralocorticoid receptor
KW - Neuronal membranes
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U2 - 10.1006/gcen.2000.7462
DO - 10.1006/gcen.2000.7462
M3 - Article
C2 - 10890568
AN - SCOPUS:0033916330
SN - 0016-6480
VL - 118
SP - 284
EP - 301
JO - General and Comparative Endocrinology
JF - General and Comparative Endocrinology
IS - 2
ER -