Elemental microanalysis of organelles in proximal tubules. II. Effects of oxygen deprivation.

This communication describes the effects of anoxia on rabbit proximal renal tubule element (ion) content by using high-resolution electron probe x-ray microanalytical imaging to obtain quantitative elemental data from subcellular compartments not previously resolvable with low-resolution imaging. These organelles and regions include the heterochromatin and euchromatin of the nucleus and the microvilli of the apical brush border, in addition to mitochondria, lysosomes, and cytoplasm. Anoxia of 40-min duration caused the expected decrease in K and increase in Na and Cl concentrations in the tubules with the cytoplasmic K:Na ratio declining to 0.13:1. These changes were accompanied by decreases in ATP and total K contents, and an increase in lactate dehydrogenase release. Swelling occurred in some cells as evidenced by ultrastructural changes. No alterations were evident after oxygen deprivation in Ca content of cytoplasm (control, 6.7 +/- 0.6 versus anoxia, 7.6 +/- 0.7 nmol/mg dry wt) or mitochondria (control, 4.0 +/- 0.4 versus anoxia, 4.9 +/- 0.6 nmol/mg dry wt) or in S content of recognizable lysosomes (control, 314 +/- 11 versus anoxia, 325 +/- 12 nmol/mg dry wt). Brush border (microvillus) Ca content was higher than cytoplasmic Ca content during normoxia (10.7 +/- 0.9 nmol/mg dry wt) and increased further during anoxia (17.0 +/- 1.0 nmol of Ca/mg dry wt). The finding of higher Ca content within the brush border region during normoxia is unexpected and novel, because such results suggest that Ca homeostasis in the apical elaboration of the proximal cell may be different from that in the cytoplasm. The results also raise the possibility that an increase in Ca content in the brush border membrane region may be involved in the pathogenesis of renal cell injury.