Venkatachalam M A, Weinberg J M
Department of Pathology, University of Texas Health Science Center at San Antonio 78284-7750.
Nephrol Dial Transplant. 1994;9 Suppl 4:15-21.
Increase of intracellular free Ca2+ (Caf) plays an important role in the deterioration of cell structure that occurs during depletion of adenosine triphosphate (ATP). On the other hand a form of Ca2+ independent cell injury due to glycine deficiency has also been recognized. Normally 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 process 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 (1.25 mM or 100 nM Ca2+) to attain high concentrations of Caf or 'clamp' Caf in the physiological range. Our results showed that structural breakdown in proximal tubule cells is compartmentalized. Increase of Caf leads to specific patterns of membrane damage and phospholipid hydrolysis. On the other hand glycine deficiency leads to a unique membrane defect that occurs independently of phospholipid breakdown and is fully expressed even if calcium-mediated injury is prevented by low Ca2+ conditions. Furthermore, the specificity of glycine was emphasized by its ability to maintain membrane continuity and thus dramatically delay lethal injury in spite of severe structural damage caused by massive increases of Caf.
细胞内游离钙离子（Caf）浓度升高在三磷酸腺苷（ATP）耗竭过程中发生的细胞结构恶化中起重要作用。另一方面，由于甘氨酸缺乏导致的一种与钙离子无关的细胞损伤形式也已被认识到。正常情况下，ATP耗竭时细胞内高浓度的甘氨酸梯度会消失。在这种情况下，外源性甘氨酸可保护细胞并独立于代谢维持细胞结构。我们研究了钙离子和甘氨酸在离体兔近端小管损伤过程中的具体作用，这些小管通过暴露于代谢抑制剂而耗竭ATP，或者通过离子载体使其对钙离子通透。小管在高钙或低钙培养基（1.25 mM或100 nM钙离子）中孵育，以在生理范围内达到高浓度的Caf或“钳制”Caf。我们的结果表明，近端小管细胞的结构破坏是有区室化的。Caf升高会导致特定模式的膜损伤和磷脂水解。另一方面，甘氨酸缺乏会导致一种独特的膜缺陷，这种缺陷独立于磷脂分解而发生，即使在低钙条件下阻止了钙介导的损伤，这种缺陷也会充分显现。此外，甘氨酸能够维持膜的连续性，从而尽管Caf大量增加导致严重的结构损伤，但仍能显著延迟致命性损伤，这突出了甘氨酸的特异性。
