Aldosterone induction of electrogenic sodium transport in the apical membrane vesicles of rat distal colon.
Na-H exchange is present in apical membrane vesicles (AMV) isolated from distal colon of normal rats. Because in intact tissue aldosterone both induces amiloride-sensitive electrogenic sodium transport and inhibits electroneutral sodium absorption, these studies with AMV were designed to establish the effect of aldosterone on sodium transport. An outward-directed proton gradient stimulated 22Na uptake in AMV isolated from distal colon of normal and dietary sodium depleted (with elevated aldosterone levels) experimental rats. Unlike normal AMV, proton gradient-dependent 22Na uptake in experimental AMV was inhibited when uptake was measured under voltage-clamped conditions. 10 microM amiloride inhibited the initial rate of proton gradient-dependent 22Na uptake in AMV of normal and experimental rats by 30 and 75%, respectively. In contrast, 1 mM amiloride produced comparable inhibition (90 and 80%) of 22Na uptake in normal and experimental AMV. Intravesicular-negative potential stimulated 22Na uptake in experimental but not in normal AMV. This increase was inhibited by 90% by 10 microM amiloride. An analogue of amiloride, 5-(N-ethylisopropyl) amiloride (1 microM), a potent inhibitor of electroneutral Na-H exchange in AMV of normal rat distal colon, did not alter potassium diffusion potential-dependent 22Na uptake. Increasing sodium concentration saturated proton gradient-dependent 22Na uptake in normal AMV. However, in experimental AMV, 22Na uptake stimulated by both proton gradient and potassium diffusion potential did not saturate as a function of increasing sodium concentration. We conclude from these results that an electrically sensitive conductive channel, not electroneutral Na-H exchange, mediates 22Na uptake in AMV isolated from the distal colon of aldosterone rats.
Rajendran
V M
VM
Department of Internal Medicine, Yale University, New Haven, Connecticut 06510.
Kashgarian
M
M
Binder
H J
HJ
D000450:Aldosterone / Q000494:pharmacology*; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D003106:Colon / Q000378:metabolism* / Q000648:ultrastructure; D004058:Diffusion; D004563:Electrochemistry; D005455:Fluorescent Antibody Technique; D007700:Kinetics; D008854:Microscopy, Electron; D011188:Potassium / Q000378:metabolism; D011522:Protons; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D012979:Sodium Radioisotopes; D014634:Valinomycin / Q000494:pharmacology
D011522:Protons; D012979:Sodium Radioisotopes; D014634:Valinomycin; D000450:Aldosterone; D000584:Amiloride; D012964:Sodium; D011188:Potassium; C039614:ethylisopropylamiloride