Garza-Quintero R, Ortega-Lopez J, Stein J H, Venkatachalam M A
Department of Pathology, University of Texas Health Science Center, San Antonio 78284.
Am J Physiol. 1990 Apr;258(4 Pt 2):F1075-83. doi: 10.1152/ajprenal.1990.258.4.F1075.
Rabbit proximal tubules were incubated aerobically or subjected to anoxia for 30 min followed by 60 min of reoxygenation. The medium contained (in mM) 5 glucose, 10 butyrate, 4 lactate or alpha-ketoglutarate (alpha-KG), and 1 alanine. Anoxic tubules in this medium were severely injured and recovered poorly. If the incubation medium was supplemented with additional alanine (up to 2.5 or 5 mM), then anoxic injury was prevented almost completely. Tubules in high-alanine medium showed modest elevations of ATP during anoxia. Comparable elevations of ATP were induced in anoxic tubules incubated with 4 mM alpha-KG and 5 mM aspartate without alanine. These substrates are metabolized anaerobically in the mitochondria to yield ATP. Surprisingly, anoxic tubules with alpha-KG and aspartate showed severe injury despite elevated ATP. If 5 mM alanine was also present, then additional increments of ATP did not occur, but injury was prevented. Examination of glucose metabolism failed to provide evidence for stimulation of anaerobic fermentations by alanine. These results suggest that alanine-induced cytoprotection during anoxia occurs by mechanisms not related to ATP synthesis, and that elevated ATP in alanine-supplemented tubules may be a result and not the cause of protection. Cytoprotection by alanine was shown to last for less than or equal to 90 min of anoxia. Glycine, a structurally related amino acid, also protects anoxic proximal tubules (J. Clin. Invest. 80: 1446, 1987). The mechanisms that underlie the cytoprotective effects of alanine and glycine remain to be determined.
将兔近端肾小管进行需氧孵育，或进行30分钟缺氧处理，随后再进行60分钟复氧处理。培养基含有（以毫摩尔计）5葡萄糖、10丁酸盐、4乳酸盐或α-酮戊二酸（α-KG）以及1丙氨酸。在此培养基中进行缺氧处理的肾小管受到严重损伤且恢复不佳。如果在孵育培养基中添加额外的丙氨酸（高达2.5或5毫摩尔），那么缺氧损伤几乎能完全得到预防。处于高丙氨酸培养基中的肾小管在缺氧期间ATP有适度升高。在不添加丙氨酸的情况下，用4毫摩尔α-KG和5毫摩尔天冬氨酸孵育的缺氧肾小管也诱导出了类似的ATP升高。这些底物在线粒体中进行无氧代谢以产生ATP。令人惊讶的是，尽管ATP升高，但含有α-KG和天冬氨酸的缺氧肾小管仍表现出严重损伤。如果同时存在5毫摩尔丙氨酸，那么ATP不会进一步升高，但损伤得到了预防。对葡萄糖代谢的检查未能提供丙氨酸刺激无氧发酵的证据。这些结果表明，缺氧期间丙氨酸诱导的细胞保护作用是通过与ATP合成无关的机制发生的，并且在添加丙氨酸的肾小管中ATP升高可能是保护的结果而非原因。丙氨酸的细胞保护作用显示可持续缺氧90分钟及以下。甘氨酸，一种结构相关的氨基酸，也能保护缺氧的近端肾小管（《临床研究杂志》80: 1446, 1987）。丙氨酸和甘氨酸细胞保护作用的潜在机制仍有待确定。
