Characterization of Na/Ca exchange in plasmalemmal vesicles from zona fasciculata cells of the bovine adrenal gland

The presence of an Na/Ca exchange system in fasciculata cells of the bovine adrenal gland was tested using isolated plasmalemmal vesicles. In the pres ence of an outwardly Nat gradient, Ca2+ uptake was about 2-fold higher than in K+ condition. Li+ did not substitute for Na+ and 5 mM Ni2+ inhibited Ca 2+ uptake. Ca2+ efflux from Ca2+-loaded vesicles was Na+-stimulated and Ni2 +-inhibited. The saturable part of Na+-dependent Ca2+ uptake displayed Mich aelis-Menten kinetics. The relationship of Na+-dependent Ca2+ uptake versus intravesicular Nai concentration was sigmoid (apparent K-0.5 approximate t o 24 mM; Hill number approximate to 3) and Na+ acted on V-max without signi ficant effect on K-m. Na+-stimulated Ca2+ uptake was temperature-dependent (apparent Q(10) approximate to 2.2). The inhibition properties of several d ivalent cations (Cd2+, Sr2+, Ni2+, Ba2+, Mn2+, Mg2+) were tested and were s imilar to those observed in kidney basolateral membrane. The above results indicate the presence of an Na/Ca exchanger located on plasma membrane of z ona fasciculata cells of bovine adrenal gland. This exchanger displays simi larities with that of renal basolateral cell membrane. (C) 2000 Elsevier Sc ience B.V. All rights reserved.