PHOSPHOLIPASE A(2) - A POTENTIALLY IMPORTANT DETERMINANT OF ADENOSINE-TRIPHOSPHATE LEVELS DURING HYPOXIC-REOXYGENATION TUBULAR INJURY

During the course of O-2 deprivation-induced proximal tubular injury, profound alterations in ATP homeostasis exist. This study sought to ch aracterize direct cellular determinants of these abnormalities further , Mouse proximal tubular segments (PTS) were isolated and their adenin e nucleotide profiles were determined during hypoxic-reoxygenation inj ury. The extent of oxidant stress, Ca2+ overload, cytoskeletal disrupt ion, and phospholipase activity were experimentally manipulated by H2O 2, Ca2+ ionophore, cytochalasin D, or PLA(2) addition, respectively. H ypoxia induced the expected deterioration in adenylate profiles, and a persistent defect in ATP homeostasis was observed during reoxygenatio n (decreased ATP/ADP ratios and absolute ATP content). H2O2, Ca2+ iono phore, and cytochalasin D had no significant impact on adenylate profi les. However, doses of PLA(2) that had no overt effect on normal tubul es caused 50 to 75% reductions in both hypoxic and reoxygenation ATP/A DP ratios and absolute ATP content. This effect was completely reprodu ced by the addition of arachidonic acid (C20:4), No other test fatty a cid (C16:0, C18:1, C18:3) reproduced this result. Despite its profound negative impact on hypoxic/reoxygenation ATP concentrations, PLA(2) a nd C20:4 each decreased lethal cell injury (lactate dehydrogenase rele ase), as previously reported. The reductions in ATP and lethal cell in jury were not mechanistically linked, because C18:1 and C18:3 reproduc ed the protective action of C20:4 without altering adenine nucleotide profiles. Ouabain, mannitol, or plasma membrane fatty acid ''scavenger '' therapy (albumin) did not improve the posthypoxic/PLA(2)-induced de pressions in ATP. The addition of C20:4 caused a modest decrease in po sthypoxic tubule oxygen consumption, compared to controls. It was conc luded that: (1) PLA(2) can be a major determinant of ATP concentration s during both hypoxic and reoxygenation tubular injury; (2) this actio n is mediated via C20:4 release; (3) a primary defect in mitochondrial ATP production, rather than increased ATP consumption, is likely to b e responsible for this action.