Elemental microanalysis of organelles in proximal tubules. I. Alterations in transport and metabolism.
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Oxygen deprivation to the kidney causes a multifactorial series of morphological, physiological, and biochemical alterations that occur as a function of time. One of the earliest events involves significant changes in the cellular contents of the physiologically important elements (ions) Na and K. Controversy exists as to the nature of changes in the content of the regulatory ion Ca, in either its free or bound form, and much less is known regarding in situ distribution and amounts of other elements such as Mg, P, S, and Cl during physiological or pathophysiological states. The objective of these studies was to evaluate element compartmentation in proximal renal tubules by using quantitative electron probe x-ray microanalysis, during specific conditions which are at least partially manifested during oxygen deprivation. Cells from control proximal tubule suspensions were compared with those exposed to (1) ouabain, to inhibit (Na+, K+)-ATPase; (2) mitochondrial uncouplers, to rapidly deplete ATP content; or (3) calcium ionophores, to cause a rapid elevation in cytoplasmic free calcium. In parallel with electron probe x-ray microanalysis imaging of subcellular elemental content, total cell potassium and ATP contents, enzyme release, oxygen consumption, cytoplasmic free calcium levels, and ultrastructural alterations were assessed. Results indicated that ATP depletion was, in the short term, more deleterious to renal proximal tubules than any of the tested ionic alterations. Intracellular organelles including mitochondria and nuclei appeared to be readily permeable to Na, K, and Cl, altering their concentrations of these ions in parallel with cytoplasmic concentrations. Lysosomes exhibited evidence of Cl accumulation, consistent with an inwardly directed proton ATPase with accompanying Cl transport. Whereas in the cytoplasm Na, K and Cl appeared to be mostly free, a large fraction of these ions within intracellular organelles seemed bound. (+info)
Elemental microanalysis of organelles in proximal tubules. II. Effects of oxygen deprivation.
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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. (+info)
Elucidating the selenium and arsenic metabolic pathways following exposure to the non-hyperaccumulating Chlorophytum comosum, spider plant.
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Variations in the composition of gelling agents affect morphophysiological and molecular responses to deficiencies of phosphate and other nutrients.
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