Effect of theophylline on binding of cortisol to cytosolic receptors of human leukocytes.

In the cytosol of human leukocytes effect of theophylline on cortisol binding was investigated by charcoal-dextran assay. The presence of theophylline enhances the rate of binding of [3H] cortisol to the receptor and increases its apparent affinity for the steroid. A high affinity (apparent association constants: without theophylline KA = 0.10 x 10(10) 1 . mol-1 and with Ka = 0.14 x 10(10) 1 . mol-1) and low capacity (number of binding sites was for both examples practically the same N = 2.7 f mol . mg-1 of protein) of binding sites for cortisol were found.