In vivo adaptation of bicarbonate reabsorption by rat distal tubules during acid loading
Levine, D.Z.; Iacovitti, M.; Buckman, S.; Vandorpe, D.; Harrison, V.; Boisvert, D.M.; Nadler, S.P.
American Journal of Physiology 267(5 Pt 2): F737-F747
1994
ISSN/ISBN: 0002-9513 PMID: 7977778 Document Number: 439082
We carried out in vivo microperfusion experiments in acid-loaded rats to characterize the adaptive response of the unidirectional components (secretory flux (J-sec) and reabsorptive flux (J-reab)) of distal tubule bicarbonate reabsorption and to test the hypothesis that J-reab is dependent on bafilomycin A-1-sensitive H+-adenosinetriphosphatase activity. During 18 h of severe acidosis there was a significant decrease in J-sec (-15 +- 3 vs. -38 +- 5 pmol cntdot min-1 cntdot mm-1, P lt 0.05) and a significant increase in J-reab (37 +- 6 vs. 0 +- 5 pmol cntdot min-1 mm-1, P lt 0.05), which was insensitive to 10-5 M bafilomycin A-1, 10-5 M Sch-28080, and 3 mM amiloride. After 3 days of acid loading, these same inhibitors reduced J-reab by apprx 60%. However, when water flux was completely inhibited by isosmotic perfusion, a significant J-reab (15 +- 2 pmol cntdot min-1 cntdot mm-1 resistant to 10-5 M bafilomycin A-1 persisted, as in severe acidosis. In reabsorbing distal tubules of overnight-fasted rats. Sch-28080 elicited no inhibition, whereas bafilomycin A-1 and amiloride had significant effects (28 +- 5, 24 +- 4, respectively, vs. 50 +- 4 pmol cntdot min-1 cntdot mm-1 for fasted rats, P lt 0.05). Thus, although J-sec is reduced in the transition from mild to severe metabolic acidosis of 18-h duration, the predominant effect is a stimulation of bafilomycin A-1-resistant J-reab.