Elemental microanalysis of organelles in proximal tubules. I. Alterations in transport and metabolism.

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.

Duke Scholars

Author Ann LeFurgey Cell Biology