Steroid-induced inhibition of adenosine transport in cultured chromaffin cells

1. Adenosine transport is subjected to regulation by hormones. Glucocorticoids, sexual steroids, and retinoic acid inhibit adenosine transport in chromaffin cells after a long-term incubation period (24 hr). No effects were observed after a short-term incubation period (10 min). 2. The kinetic parameters of transporters were studied. No significant changes were observed for the affinity constant (Km), whose value remains at 1 +/- 0.2 microM after 24-hr incubation in the presence of these compounds. The maximal velocity (Vmax) was significantly modified, with a decrease of about 20% in all cases. 3. NBTI binding was not modified in its affinity constant or maximal bound capacity (Bmax) by the presence of these compounds for a 24-hr incubation period. Thus the efficiency of transporters (quotient Vmax/Bmax) changed from 10.9 +/- 0.08 adenosine molecules transported per transporter per sec in the control cells to 9.1 +/- 0.07 in hormone-treated cultured cells. 4. The thyroid hormone (T3) significantly increased adenosine transport in a long-term incubation period in chromaffin cells (24 hr). This activatory effect is antagonized by steroid hormones and retinoic acid.