[Binding of glucocorticoids by a transcortin-like protein in the cytoplasmic fraction of rat myocardium].

Myocardial cytosol of adult adrenalectomized rats bound specifically 3H-corticosterone and 3H-hydrocortisone and did not bind the synthetic 9alpha-fluoroglucocorticoid (dexamethasone) in vitro at 0-4 degrees. The specific binding of dexamethasone was not also found in the cytosol of neonatal rats. Heating of myocardial cytosol of adrenalectomized rats within 10 min at 60 degrees led to the complete loss of the glucocorticoid-binding activity. Treatment of the cytosol within the same period but at the temperature lower than 55 degrees did not affect its binding capacity. 3H-corticosterone-cytoreceptor complex was precipitated by ammonium sulphate at 40-60% of saturation. The complex was eluted from a column of Sephadex G-150 by solutions with both low (0.015 M KCl) and high (0.4 M KCl) ionic strength as the alone peak. This fraction corresponded by molecular weight to the transcortin complex. The data obtained and the results of our previous investigations suggest that myocardial glucocorticoid-binding cytoplasmic protein is related to transcortin-like cytoreceptors.