Demonstration of specific glucocorticoid binding sites in bovine cornea

Abstract

Specific [ 3H]-dexamethasone binding sites were demonstrated in bovine corneal cytosol using titration analyses. Specific glucocorticoid binding to corneal cytosol exhibited a single class of sites with apparent dissociation constants of 4–6 n m and 68–72 fmol binding sites mg −1 cytosolic protein. Association of steroid with these binding sites was temperature- and time-dependent. Specific binding was maximal at 4°C after 6 hr and was somewhat lower at 25°C and lowest at 37°C. Presence of increasing amounts of certain unlabeled steroids with glucocorticoid activity inhibited [ 3H]-dexamethasone binding in a dose-dependent manner. The order, beginning with the most potent inhibitor of binding, was triamcinolone acetonide > fluorometholone > dexamethasone > medroxy progesterone acetate > 11β-OH-progesterone > prednisolone acetate > prednisolone > cortisol > corticosterone. Other steroids exhibiting less inhibition of [ 3H]-dexamethasone binding were cortexolone > prednisone > dexamethasone phosphate > progesterone > prednisolone phosphate > cortisone > 17α-OH progesterone > estradiol-17β > testosterone > 11α, 17α,21-OH-progesterone. These data suggest that the influence of glucocorticoids and drugs with this type of normal activity on corneal cells is mediated by an intracellular receptor protein.