Effects of aldosterone on (Na+ + K+)-ATPase of amphibian sodium-transporting epithelial cells (A6) in culture.
Stimulation by aldosterone of sodium reabsorption can be reproduced on a cell line, A6, derived from the renal tissue of Xenopus laevis. These cells organize themselves as a polarized epithelium carrying out unidirectional sodium transport, reflected by the short-circuit current (Isc). Isc response to aldosterone starts to be apparent after a latency period of 2-3 h; the full hormonal effect takes much longer. On the other hand, (Na+ + K+)-ATPase activity and density in ouabain binding sites did not increase before several hours of treatment. At that stage, while Isc more than trebled, Na+ pump activity and density went up by less than 50%. A significant influence of aldosterone on the way the Na+ pump operates is considered unlikely, since cell interaction with ouabain remained unchanged (Kd approximately 18 nM). Furthermore, the close correspondence of hormonal effect, in relative terms, on (Na+ + K+)-ATPase activity vs density, argues against a significant degree of recruitment of spare pump units. Thus aldosterone effect on Na+ pump probably results from increased biosynthesis of the enzyme. The aldosterone dependent Na+ pump stimulation is apparently unrelated to sodium available for transport. The hormone seems to act on Na+ pump directly.
Leal
T
T
Department of Physiology, U.C.L. Medical School, Brussels, Belgium.
Crabbé
J
J
D000450:Aldosterone / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D004553:Electric Conductivity; D004848:Epithelium / Q000201:enzymology / Q000502:physiology; D007668:Kidney; D007700:Kinetics; D010042:Ouabain / Q000378:metabolism / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014982:Xenopus laevis
D000450:Aldosterone; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase