Distal tubule unidirectional HCO3 reabsorption in vivo during acute and chronic metabolic alkalosis in the rat
Levine, D.Z.; Iacovitti, M.; Buckman, S.; Vandorpe, D.; Harrison, V.; Nadler, S.P.
American Journal of Physiology 266(6 Pt 2): F919-F925
1994
ISSN/ISBN: 0002-9513 PMID: 8023971 Document Number: 423312
During metabolic alkalosis (MA) associated with 2 days of dietary chloride restriction, there is net bicarbonate secretion by rat distal tubules in vivo, whereas after 5 wk of chloride depletion alkalosis there is net bicarbonate reabsorption. To examine unidirectional components of net bicarbonate reabsorption during chronic MA, we measured distal tubule unidirectional bicarbonate secretion (J-sec) and reabsorption (Jr,ab), as well as the inhibitor sensitivity of J-reab. In control, 2-day, and 7-day alkalosis, J-sec was similar. J-reab, however, was only present in 7-day MA (17 +- 3 pmol cntdot min-1 cntdot mm-1, P lt 0. 05). This J-reab was completely suppressed by perfusion with 10-7 M bafilomycin A-1, partially suppressed with 10-5 M Schering (Sch)-28080 (4 +- 2 pmol cntdot min-1 cntdot mm-1, P lt 0.1), and converted into a secretory flux by 3 mM amiloride. We conclude that adaptation to chloride depletion MA from the acute secretory phase to the chronic state, where plasma bicarbonate is sustained at elevated levels, does not involve suppression of distal tubule J-sec but rather enhanced J-reab, which is sensitive to bafilomycin, Sch-28080, and amiloride.