title: Cortisol binding in rat skeletal muscle.
abstract: Studies of the reversible binding of [3H]cortisol by rat gastrocnemius muscle cytoplasm in vitro reveal specific binding in the 27,000 times g supernatant fraction at 0 degrees. The [3H]cortisol-binding molecule had an apparant Kd value of 1.7 times 10-7 M and the number of binding sites was 0.99 pmol per mg of cytosol protein. Only a single class of [3H]cortisol-binding sites could be detected, whose protein nature was suggested by its susceptibility to nagarse. The [3H]cortisol-protein complex sedimented at similar to 4 S in a 5 to 20% sucrose gradient either in the presence or absence of 0.3 M KCl. Binding increased more than 2-fold in adrenalectomized rats and was markedly reduced in the muscle of rats pretreated with cortisol. In contrast to the binding of [3H]dexamethasone and [3H]triamcinolone acetonide to receptor proteins in muscle, no correlation was found between the ability of various steroids to complete wtth [3H]cortisol binding and their glucocorticoid potency: [3H]cortisol binding was inhibited by a 1000-fold higher concentration of unlabeled cortisol and progesterone but not by dexamethasone or triamcinolone acetonide. It is therefore suggested that the [3H]cortisol-binding reaction is not directly involved in the biological effects of all potent glucocorticoids in skeletal muscle. The [3H]cortisol-binding protein in muscle cytosol could not be unequivocally distinguished from rat plasma corticosteroid-binding globulin, because both had similar steroid specificity and temperature stability, were not markedly affected by--SH reagents, and displayed similar sedimentation properties.
mesh_terms: D000311:Adrenal Glands / Q000502:physiology; D000315:Adrenalectomy; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D003907:Dexamethasone / Q000378:metabolism; D005033:Ethylmaleimide / Q000494:pharmacology; D006854:Hydrocortisone / Q000378:metabolism* / Q000494:pharmacology; D007461:Iodoacetates / Q000494:pharmacology; D007700:Kinetics; D009124:Muscle Proteins / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism*; D011374:Progesterone / Q000494:pharmacology; D011485:Protein Binding; D051381:Rats; D011956:Receptors, Cell Surface; D012910:Snake Venoms / Q000494:pharmacology; D013997:Time Factors; D014222:Triamcinolone Acetonide / Q000378:metabolism
chemical_list: D007461:Iodoacetates; D009124:Muscle Proteins; D011956:Receptors, Cell Surface; D012910:Snake Venoms; D011374:Progesterone; D003907:Dexamethasone; D014222:Triamcinolone Acetonide; D005033:Ethylmaleimide; D006854:Hydrocortisone