Modulation by Gly, Ca, and acidosis of injury-associated unesterified fatty acid accumulation in proximal tubule cells

We have examined the dependence of unesterified fatty acid accumulation by intact, freshly isolated proximal tubules on Ca²⁺, pH, and the cytoprotective amino acid, glycine, during injury induced by hypoxia, antimycin, or antimycin plus ionomycin. In the absence of glycine, similarly high levels of fatty acid accumulation were seen during all three injury conditions irrespective of whether tubules were incubated in normal 1.25 mM Ca²⁺ medium or in medium where Ca²⁺ was buffered to 0.1 μM, a maneuver which prevented injury-associated increase of cytosolic-free Ca²⁺ as measured with fura 2. In the presence of glycine, which strongly suppressed development of lethal membrane damage for at least 60 min and did not have any apparent direct effects on fatty acid accumulation, both Ca²⁺- independent and Ca²⁺dependent components of fatty acid accumulation were discernible. The Ca²⁺ -independent component accounted for ~2/3 of fatty acid accumulation and did not vary as Ca²⁺ ranged from 10 nM to 1 μM. Unequivocal Ca²⁺-dependent accumulation occurred when Ca²⁺ exceeded 10 μM. 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 the modulatory actions of the potent, intrinsic cytoprotective factors, glycine and reduced pH, and provide insight into the relationship between fatty acid accumulation and lethal membrane damage.