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°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 < 0.005); phosphatidylcholine fraction in acidotic toads was 80,462 ± 16,862 and in normal bladders was 26,892 ± 5,198 (P < 0.025); and the phosphatidylethanolamine (PE) fraction in acidotic was 48,665 ± 10,998 and in normal animals was 17,441 ± 3,905 (P < 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 < 0.05) and for PE acidotic bladders was 9,129 ± 1,304 and in normal bladders was 3,285 ± 416 (P < 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 < 0.01 for both).