MODULATION BY GLY, CA, AND ACIDOSIS OF INJURY-ASSOCIATED UNESTERIFIEDFATTY-ACID ACCUMULATION IN PROXIMAL TUBULE CELLS

We have examined the dependence of unesterified fatty acid accumulatio n by intact, freshly isolated proximal tubules on Ca2+, pH, and the cy toprotective amino acid, glycine, during injury induced by hypoxia, an timycin, or antimycin plus ionomycin. In the absence of glycine, simil arly high levels of fatty acid accumulation were seen during all three injury conditions irrespective of whether tubules were incubated in n ormal 1.25 mM Ca2+ medium or in medium where Ca2+ was buffered to 0.1 mu M, a maneuver which prevented injury-associated increase of cytosol ic-free Ca2+ as measured with fura 2. In the presence of glycine, whic h strongly suppressed development of lethal membrane damage for at lea st 60 min and did not have any apparent direct effects on fatty acid a ccumulation, both Ca2+-independent and Ca2+-dependent components of fa tty acid accumulation were discernible. The Ca2+-independent component accounted for similar to 2/3 of fatty acid accumulation and did not v ary as Ca2+ ranged from 10 nM to 1 mu M. Unequivocal Ca2+-dependent ac cumulation occurred when Ca2+ exceeded 10 mu M. Lowering pH to 6.9 had a moderate, generalized suppressive effect on fatty acid accumulation , including the major Ca2+-independent component, irrespective of the presence of glycine. These data emphasize the role of Ca2+-independent fatty acid accumulation during proximal tubule cell injury, clarify t he modulatory actions of the potent, intrinsic cytoprotective factors, glycine and reduced pH, and provide insight into the relationship bet ween fatty acid accumulation and lethal membrane damage.