Abstract
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.
Highlights
Na-H exchange is present in apical membrane vesi- of the coupling of Na-H andC1-HCO, exchanges
It is likely that overall electroneutral NaCl absorptionis the result by the method of Stieger et al [14], identified Na-H exchange in that an outward-directed proton gradient stimulated 22Na uptake [8].their vesicles did not demonstrate transient accumulation, and atequilibrium there was a significant difference in 22Na uptake pirnesence and absence of proton gradient [8]
Preparation of Apical Membrane Vesicles-apical membrane vesicles (AMV) of normal and experimental rat distal colon were isolated by the method of Stieger et al (141, as described by Binder et al [8], with additional modification in the final centrifugation
Summary
A from apical membranes; we have modified the uptake conditions so that the equilibrium values are similar in both the presence and absenceof a proton gradient and that transient accumulation isobserved in the presencoef a proton gradient. This study demonstrates that aldosterone induceasmiloridesensitive potassiumdiffusion potential-dependent and proton gradient-linked sodiumconductive channel in AMV of rat distal colon
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