Intestinal ion transport and intracellular pH during acute respiratory alkalosis and acidosis.

Acute respiratory alkalosis and acidosis alter rat ileal and colonic but not jejunal electrolyte transport. To examine the role of altered intracellular pH, pHi, and HCO3 concentration, (HCO3)i, we measured pHi in mucosa scraped from the jejunum, ileum, and colon of anesthetized, mechanically ventilated Sprague-Dawley rats. During states of respiratory alkalosis (Pco2 24.9 +/- 0.8 mmHg, pH 7.586 +/- 0.014), respiratory acidosis (Pco2 67.8 +/- 1.2 mmHg, pH 7.228 +/- 0.007), and normocapnia (Pco2 41.1 +/- 0.7 mmHg, pH 7.401 +/- 0.006), pHi was measured by determining the distribution of 5,5-dimethyl[2-14C]oxazolidine-2,4-dione, using [3H]inulin as a marker of extracellular space. (HCO3)i was calculated using portal vein Pco2. In the ileum, the pHi of 6.901 +/- 0.029 was similar in alkalosis [(HCO3)i 5.4 +/- 0.3 mM], acidosis [(HCO3)i 12.4 +/- 0.6 mM], and normocapnia [(HCO3)i 8.6 +/- 0.8 mM). In both the jejunum and colon, pHi was increased in alkalosis [pHi 6.998 +/- 0.038, (HCO3)i 6.7 +/- 0.6 mM] and decreased in acidosis [pHi 6.789 +/- 0.024, (HCO3)i 10.4 +/- 0.6 mM] as compared with normocapnia [pHi 6.915 +/- 0.026, (HCO3)i 8.9 +/- 0.7 mM] (colon data given). Net electrolyte transport measured by in vivo perfusion revealed that ileal and colonic, but not jejunal, net Na and Cl absorption was decreased during alkalosis and increased during acidosis. These data suggest that, during respiratory acidosis and alkalosis, pHi is maintained in a qualitatively similar way in the jejunum, ileum, and colon with quantitatively greater or lesser changes in (HCO3)i.(ABSTRACT TRUNCATED AT 250 WORDS)