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

Ilse Smets, Adrian Caplanusi, Sanda Despa, Zsolt Molnar, Mihai Radu, Martin VandeVen, Marcel Ameloot, Paul Steels

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Abstract

In ischemic or hypoxic tissues, elevated Ca2+ levels have emerged as one of the main damaging agents among other Ca2+ -independent mechanisms of cellular injury. Because mitochondria, besides the endoplasmic reticulum, play a key role in the maintainance of cellular Ca 2+ homeostasis, alterations in the mitochondrial Ca2+ content ([Ca2+]m) were monitored in addition to changes in cytosolic Ca2+ concentration ([Ca2+]i) during metabolic inhibition (MI) in renal epithelial Madin-Darby canine kidney (MDCK) cells. [Ca2+]i and [Ca2+]m were monitored via, respectively, fura 2 and rhod 2 measurements. MI induced an increase in [Ca2+]i reaching 631 ± 78 nM in ∼20 min, followed by a decrease to 118 ± 9 nM in the next ∼25 min. A pronounced drop in cellular ATP levels and a rapid increase in intracellular Na+ concentrations in the first 20 min of MI excluded Ca2+ efflux in the second phase via plasma membrane ATPases or Na+/Ca2+ exchangers (NCE). Mitochondrial rhod 2 intensities increased to 434 ± 46% of the control value during MI, indicating that mitochondria sequester Ca2+ during MI. The mitochondrial potential (δΨm) was lost in 20 min of MI, excluding mitochondrial Ca2+ uptake via the δΨ m-dependent mitochondrial Ca2+ uniporter after 20 min of MI. Under Na+-free conditions, or when CGP-37157, a specific inhibitor of the mitochondrial NCE, was used, no drop in [Ca2+] 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 Ca2+ via the NCE acting in the reverse mode.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Renal Physiology
Volume286
Issue number4 55-4
StatePublished - Apr 2004
Externally publishedYes

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Keywords

  • CGP-37157
  • Intramitochondrial calcium
  • Renal epithelial cells
  • Rhod 2

ASJC Scopus subject areas

  • Physiology

Cite this

Smets, I., Caplanusi, A., Despa, S., Molnar, Z., Radu, M., VandeVen, M., Ameloot, M., & Steels, P. (2004). Ca2+ uptake in mitochondria occurs via the reverse action of the Na+/Ca2+ exchanger in metabolically inhibited MDCK cells. American Journal of Physiology - Renal Physiology, 286(4 55-4).