title: Steroid-induced inhibition of adenosine transport in cultured chromaffin cells.
abstract: 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.
authors.affiliation: Department of Biochemistry, Veterinary Faculty, Complutense University, Madrid, Spain.
authors.forename: M D
authors.initials: MD
authors.lastname: Fideu
authors.forename: M T
authors.initials: MT
authors.lastname: Miras-Portugal
mesh_terms: D000241:Adenosine / Q000378:metabolism*; D000313:Adrenal Medulla / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000345:Affinity Labels / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology; D006728:Hormones / Q000494:pharmacology; D007700:Kinetics; D013256:Steroids / Q000494:pharmacology*; D013868:Thioinosine / Q000031:analogs & derivatives / Q000378:metabolism; D014212:Tretinoin / Q000494:pharmacology; D014284:Triiodothyronine / Q000494:pharmacology
chemical_list: D000345:Affinity Labels; D002352:Carrier Proteins; D006728:Hormones; D013256:Steroids; D014284:Triiodothyronine; D013868:Thioinosine; D014212:Tretinoin; D003907:Dexamethasone; C001789:4-nitrobenzylthioinosine; D000241:Adenosine