DISTAL TUBULE UNIDIRECTIONAL HCO3 REABSORPTION IN-VIVO DURING ACUTE AND CHRONIC METABOLIC ALKALOSIS IN THE RAT

During metabolic alkalosis (MA) associated with 2 days of dietary chlo ride restriction, there is net bicarbonate secretion by rat distal tub ules 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 (J(reab)), as well as the inhibitor sensitivity of J(reab). In contro l, 2-day, and 7-day alkalosis, J(sec) was similar. J(reab), however, w as only present in 7-day MA (17 +/- 3 pmol.min(-1).mm(-1), P < 0.05). This J(reab) was completely suppressed by perfusion with 10(-7) M bafi lomycin A(1), partially suppressed with 10(-5) M Schering (Sch)-28080 (4 +/- 2 pmol.min(-1).mm(-1) P < 0.1), and converted into a secretory flux by 3 mM amiloride. We conclude that adaptation to chloride deplet ion MA from the acute secretory phase to the chronic state, where plas ma bicarbonate is sustained at elevated levels, does not involve suppr ession of distal tubule J(sec) but rather enhanced J(reab), which is s ensitive to bafilomycin, Sch-28080, and amiloride.