Docosahexaenoic acid and other fatty acids induce a decrease in pHi in Jurkat T-cells.
1. Docosahexaenoic acid (DHA) induced rapid (t1/2=33 s) and dose-dependent decreases in pHi in BCECF-loaded human (Jurkat) T-cells. Addition of 5-(N,N-dimethyl)-amiloride, an inhibitor of Na+/H+ exchanger, prolonged DHA-induced acidification as a function of time, indicating that the exchanger is implicated in pHi recovery. 2. Other fatty acids like oleic acid, arachidonic acid, eicosapentaenoic acid, but not palmitic acid, also induced a fall in pHi in these cells. 3. To assess the role of calcium in the DHA-induced acidification, we conducted experiments in Ca2+-free (0% Ca2+) and Ca2+-containing (100% Ca2+) buffer. We observed that there was no difference in the degree of DHA-induced transient acidification in both the experimental conditions, though pHi recovery was faster in 0% Ca2+ medium than that in 100% Ca2+ medium. 4. In the presence of BAPTA, a calcium chelator, a rapid recovery of DHA-induced acidosis was observed. Furthermore, addition of CaCl2 into 0% Ca2+ medium curtailed DHA-evoked rapid pHi recovery. In 0% Ca2+ medium, containing BAPTA, DHA did not evoke increases in [Ca2+]i, though this fatty acid still induced a rapid acidification in these cells. These observations suggest that calcium is implicated in the long-lasting DHA-induced acidosis. 5. DHA-induced rapid acidification may be due to its deprotonation in the plasma membrane (flip-flop model), as suggested by the following observations: (1) DHA with a -COOH group induced intracellular acidification, but this fatty acid with a -COOCH3 group failed to do so, and (2) DHA, but not propionic acid, -induced acidification was completely reversed by addition of fatty acid-free bovine serum albumin in these cells. 6. These results suggest that DHA induces acidosis via deprotonation and Ca2+ mobilization in human T-cells.
Aires
Virginie
V
UPRES Lipides and Nutrition, Université de Bourgogne, Faculté des Sciences de la vie, 6, Boulevard Gabriel, Dijon 21000, France.
Hichami
Aziz
A
Moutairou
Kabirou
K
Khan
Naim Akhtar
NA
D004281:Docosahexaenoic Acids / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology*; D005452:Fluoresceins; D006801:Humans; D006863:Hydrogen-Ion Concentration / Q000187:drug effects*; D019169:Jurkat Cells; D018613:Microscopy, Confocal
D005231:Fatty Acids, Unsaturated; D005452:Fluoresceins; C057433:2',7'-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester; D004281:Docosahexaenoic Acids