Ca2+ uptake in mitochondria occurs via the reverse action of the Na+/Ca2+ exchanger in metabolically inhibited MDCK cells (original) (raw)

2004, AJP: Renal Physiology

7 other HighWire-hosted articles: This article has been cited by http://ajprenal.physiology.org/content/286/4/F784#cited-by including high resolution figures, can be found at: Updated information and services http://ajprenal.physiology.org/content/286/4/F784.full found at: can be American Journal of Physiology -Renal Physiology about Additional material and information Ca 2ϩ uptake in mitochondria occurs via the reverse action of the Na ϩ /Ca 2ϩ exchanger in metabolically inhibited MDCK cells. Am J Physiol Renal Physiol 286: F784-F794, 2004. First published December 9, 2003; 10.1152/ajprenal.00284.2003.-In ischemic or hypoxic tissues, elevated Ca 2ϩ levels have emerged as one of the main damaging agents among other Ca 2ϩ -independent mechanisms of cellular injury. Because mitochondria, besides the endoplasmic reticulum, play a key role in the maintainance of cellular Ca 2ϩ homeostasis, alterations in the mitochondrial Ca 2ϩ content ([Ca 2ϩ ]m) were monitored in addition to changes in cytosolic Ca 2ϩ concentration ([Ca 2ϩ ]i) during metabolic inhibition (MI) in renal epithelial Madin-Darby canine kidney (MDCK) cells. [Ca 2ϩ ]i and [Ca 2ϩ ]m were monitored via, respectively, fura 2 and rhod 2 measurements. MI induced an increase in [Ca 2ϩ ]i reaching 631 Ϯ 78 nM in ϳ20 min, followed by a decrease to 118 Ϯ 9 nM in the next ϳ25 min. A pronounced drop in cellular ATP levels and a rapid increase in intracellular Na ϩ concentrations in the first 20 min of MI excluded Ca 2ϩ efflux in the second phase via plasma membrane ATPases or Na ϩ /Ca 2ϩ exchangers (NCE). Mitochondrial rhod 2 intensities increased to 434 Ϯ 46% of the control value during MI, indicating that mitochondria sequester Ca 2ϩ during MI. The mitochondrial potential (⌬⌿m) was lost in 20 min of MI, excluding mitochondrial Ca 2ϩ uptake via the ⌬⌿m-dependent mitochondrial Ca 2ϩ uniporter after 20 min of MI. Under Na ϩ -free conditions, or when CGP-37157, a specific inhibitor of the mitochondrial NCE, was used, no drop in [Ca 2ϩ ]i was seen during MI, whereas the MI-induced increase in mitochondrial rhod 2 fluorescence was strongly reduced. To our knowledge, this study is the first to report that in metabolically inhibited renal epithelial cells mitochondria take up Ca 2ϩ via the NCE acting in the reverse mode. renal epithelial cells; intramitochondrial calcium; rhod 2; CGP-37157 CELLULAR CA 2ϩ OVERLOAD IS an important determinant of ischemic cellular injury, because an excessive increase in cytosolic Ca 2ϩ concentration ([Ca 2ϩ ] i ) might activate different Ca 2ϩdependent catabolic enzymes such as phospholipases, proteases, and endonucleases. Therefore, excessive elevation of *I. Smets, A. Caplanusi, and S. Despa contributed equally to this report.