Calcium and free radicals in hypoxia/reoxygenation injury of renal epithelial cells

Eddie L. Greene, Mark S Paller

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60 Scopus citations


Hypoxia and reoxygenation (H/R) gener-ate oxygen free radicals that result in renal cell injury. We tested the roles of calcium and calmodulin in mediating xanthine oxidase-derived oxygen free radical production during H/R. Lowering extracellular Ca2+ attenuated lethal cell injury. H/R increased Superoxide radical production over basal levels, whereas removing extracellular Ca2+ before hypoxia decreased Superoxide radical production to basal levels. Pretreatment with either 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate hydrochloride or thapsigargin, to inhibit release or deplete stores of intracellular Ca2+, did not affect injury following H/R. Ionomycin increased lactate dehydrogenase release during H/R but did not increase superoxide radical to levels greater than that observed for H/R alone. The calmodulin inhibitors trifluoperazine, calmidazolium, or N-(6-aminohexyl)-5-chloro-l-naphthalenesulfonamide decreased cell injury to varying degrees. Trifluoperazine also decreased superoxide radical production during H/R and was shown to inhibit the conversion of xanthine dehydrogenase to xanthine oxidase. Cell injury and superoxide radical production correlated with cytosolic free Ca2+ during H/R as determined with the Ca2+-sensitive fluoroprobe indo 1. Cytosolic free Ca2+ increased slightly during hypoxia and showed a dramatic increase as soon as cells were reoxygenated. Cells incubated in a Ca2+-free medium actually showed a small decrease in intracellular Ca2+ despite H/R. In summary, Ca2+ derived from extracellular sources promoted superoxide radical production and renal cell injury by a calmodulin-dependent conversion of xanthine dehydrogenase to xanthine oxidase, a major source of oxygen free radicals during H/R.

Original languageEnglish (US)
Pages (from-to)F13-F20
JournalAmerican Journal of Physiology - Renal Physiology
Issue number1
StatePublished - 1994


  • Calmodulin
  • Oxygen free radical
  • Protease
  • Xanthine oxidase


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