PHOSPHOLIPASE A(2)-INDUCED CYTOPROTECTION OF PROXIMAL TUBULES - POTENTIAL DETERMINANTS AND SPECIFICITY FOR ATP DEPLETION-MEDIATED INJURY

Addition of phospholipase A(2) (PLA(2)) to isolated proximal tubular s egments (PTS) has previously been shown to decrease hypoxic cell death without altering ATP concentrations. The study presented here was und ertaken to identify determinant(s) of this protection, and to define t he spectrum of injuries against which it can operate. PTS were extract ed from mouse kidneys and subjected to diverse forms of injury (hypoxi a/reoxygenation, antimycin A, Ca2+ ionophore, amphotericin B, FeSO4, a nd myohemoglobin). In subtoxic doses, addition of PLA(2) significantly reduced hypoxic- and antimycin A-induced injury (percentage of lactat e dehydrogenase release); however, a dose-dependent exacerbation of al l other forms of injury resulted. The ability of PLA(2) to mitigate hy poxic injury remained intact despite the inhibition of Na,K-ATPase (ou abain) or the inducement of cytoskeletal disruption (cytochalasin D). However, it was negated by minimally toxic amphotericin B or Ca2+ iono phore doses, indicating its dependence on preserved ionic gradients. N evertheless, neither lowering/removing buffer Ca2+ or NaCl concentrati ons, nor hypertonic mannitol addition reproduced the cytoprotective ef fect of PLA(2). PLA(2) induced synergistic deacylation in hypoxic tubu les, suggesting that unsaturated fatty-acid accumulation might mediate its cytoprotective effect. The fact that the addition of exogenous ar achidonate, but not palmitate, to tubules protected against hypoxia, b ut worsened nonhypoxic forms of injury, supported this hypothesis. Sin ce arachidonate might induce ''feedback'' inhibition of intracellular PLA(2), the ability of an intracellular phospholipase inhibitor (ONO-R S-082; Biomol, Plymouth, PA) to blunt hypoxic damage was tested. This agent fully reproduced the cytoprotective effect of PLA(2). It was con cluded that: (1) PLA(2)-induced cytoprotection is relatively specific for ATP depletion injury; (2) it is dependent on, but not explained by , maintenance of NaCl and Ca2+ gradients; (3) it does not require Na,K -ATPase activity or cytoskeletal integrity for its expression; and (4) extracellular PLA(2), via arachidonate release, may cause feedback in hibition of intracellular PLA(2), thereby protecting critical intracel lular targets from attack.