Binding of dexamethasone and inhibition of transport of 3-O-methylglucose in rat thymocytes.
The effect of temperature (21-37 degrees C) on binding of [3H]dexamethasone in intact rat thymocytes was investigated. Receptor binding was correlated with inhibition by dexamethasone of in vitro transport of 3-O-[14C]methyl-D-glucose at 37 degrees C. Receptor binding of dexamethasone was dependent on temperature. The number of receptors per cell was about 3000 at all temperatures studied. However, an increase of temperature from 21 to 37 degrees C changed the rate constant of dissociation from 6.0 . 10(-3) min-1 to 55.0 . 10(-3) min-1, and the dissociation constant from 1.1 to 5.9 nM. The effect of dexamethasone (0.8-790 nM) on transport of 3-O-[14C]-methyl-D-glucose (10-50 muM) was investigated during the initial 30 s of uptake at 37 degrees C. A dose-dependent inhibition of transport was found at 60 and 120 min after the addition of hormone. Correlation between effect and receptor occupancy was linear. Maximal inhibition was achieved at concentrations of dexamethasone resulting in 95-97% receptor occupancy, and 50% of the maximal effect was obtained at a concentration of dexamethasone corresponding to 50% receptor occupancy. Inhibition of transport differed in latency between cell preparations. However, this could not be ascribed to change of either amount of affinity of dexamethasone receptors.
D000818:Animals; D001693:Biological Transport, Active; D003907:Dexamethasone / Q000378:metabolism* / Q000494:pharmacology; D007700:Kinetics; D008757:Methylglucosides / Q000378:metabolism*; D008759:Methylglycosides / Q000378:metabolism*; D051381:Rats; D011965:Receptors, Glucocorticoid / Q000378:metabolism*; D011987:Receptors, Steroid / Q000378:metabolism*; D013696:Temperature; D013950:Thymus Gland / Q000187:drug effects / Q000378:metabolism*
D008757:Methylglucosides; D008759:Methylglycosides; D011965:Receptors, Glucocorticoid; D011987:Receptors, Steroid; D003907:Dexamethasone