MECHANISMS OF CELL INJURY IN ATP-DEPLETED PROXIMAL TUBULES - ROLE OF GLYCINE, CALCIUM, AND POLYPHOSPHOINOSITIDES

Increase of intracellular free Ca2+ (Caf) plays an important role in t he deterioration of cell structure that occurs during depletion of ade nosine triphosphate (ATP). On the other hand a form of Ca2+ independen t cell injury due to glycine deficiency has also been recognized. Norm ally high intracellular gradients of glycine are dissipated during ATP depletion. Under these circumstances exogenous glycine protects cells and preserves structure independently of metabolism. We have examined the specific contributions of calcium and glycine to the injury proce ss in isolated rabbit proximal tubules depleted of ATP by exposure to a metabolic inhibitor, or additionally made permeable to calcium ions by an ionophore. Tubules were incubated in high or low Ca2+ media (1.2 5 mM or 100 nM Ca2+) to attain high concentrations of Caf or 'clamp' C af in the physiological range. Our results showed that structural brea kdown in proximal tubule cells is compartmentalized. Increase of Caf l eads to specific patterns of membrane damage and phospholipid hydrolys is. On the other hand glycine deficiency leads to a unique membrane de fect that occurs independently of phospholipid breakdown and is fully expressed even if calcium-mediated injury is prevented by low Ca2+ con ditions. Furthermore, the specificity of glycine was emphasized by its ability to maintain membrane continuity and thus dramatically delay l ethal injury in spite of severe structural damage caused by massive in creases of Caf.