Factors influencing nonspecific binding of glucocorticoids in myocardial tissue.

Myocardial slices from the left ventricle of cat hearts were incubated in Krebs-Henseleit buffer containing 10 mM glucose which were gassed with 95% O2 and 5% CO2. Tritiated dexamethasone (DEXA 0.171 MM) or methylprednisolone (MP 0.805 mM) was added under varying conditions of temperature, pH, and in the presence of various metabolic inhibitors. Glucocorticoid uptake by myocardial tissue was found to be temperature-dependent, plateauting after 60 min of incubation at 0.21 mumole of DEXA/g of tissue and 0.95 mumole of MP/g of tissue at 37 degrees. Steroid uptake was retarded about 50% at 0 degrees. Increasing the concentration of either steroid resulted in a linear increase in the uptake of that steroid. Incubation in the presence of metabolic or SH-inhibitors produced no significant changes in glucocorticoid uptake. Optimal glucocorticoid uptake occurred between pH 7.3-7.4. Thus, myocardial cells appear to be able to take up large quantities of glucocorticoids, but the uptake process does not appear to be energy-dependent.