Phospholipid changes during adaptation to acidosis in urinary bladder of Bufo marinus

The purpose of this study was to determine whether phospholipids (PL) play a role in the adaptation to metabolic acidosis by toad urinary bladder epithelium. Toads were placed in an NH4Cl acidosis for 48 hr. Quarter bladders were removed and incubated with [32P]orthophosphate or [3H]arachidonic acid for 1 hr at 25 degrees C. PL were detected by thin layer chromatography, autoradiography, and quantitated by liquid scintillation counting or fractional amounts were determined from phosphate content and expressed as counts per minute per micromolar of total phosphate or as percentage of fraction of total PL. Incorporation of [3H]arachidonic acid into urinary bladder PL was measured in acidotic and normal toads. There was a higher rate of arachidonic acid incorporation into several PL in acidotic animals. Phosphatidic acid and phosphatidylserine fraction in acidosis was 37,705 +/- 6,821 and in normal bladders was 9,254 +/- 2,652 (P less than 0.005); phosphatidylcholine fraction in acidotic toads was 80,462 +/- 16,862 and in normal bladders was 26,892 +/- 5,198 (P less than 0.025); and the phosphatidylethanolamine (PE) fraction in acidotic was 48,665 +/- 10,998 and in normal animals was 17,441 +/- 3,905 (P less than 0.025). 32P labeling revealed a higher rate of incorporation in bladders from acidotic toads compared with normal toads. In the acidotic bladders, the phosphatidic acid and phosphatidylserine fraction was 19,754 +/- 3,597 and in normal bladders was 12,980 +/- 1,394 (P less than 0.05) and for PE acidotic bladders was 9,129 +/- 1,304 and in normal bladders was 3,285 +/- 416 (P less than 0.001). Fractional PL (reported as percentage of fraction of total PL based on total lipid phosphorus) analysis in normal toads revealed phosphatidylinositol = 8.1 +/- 0.6% and PE = 27 +/- 1.2%, whereas for acidotic toads phosphatidylinositol = 11 +/- 0.6% and PE = 32 +/- 1.0% (P less than 0.01 for both). Aldosterone, a known stimulator of acidification, had no effect on 32P incorporation into PL fractions of the bladder. The increase in PL turnover following induction of acidosis is consistent with increased membrane synthesis or turnover during metabolic acidosis and this may reflect an increased transport of vesicular H+-ATPase into the apical membrane or the result of a proliferation of acid-secreting mitochondria-rich cells or both.