Received September 1, 2004
Revised October 21, 2004
Accepted after revision November 8, 2004
GI and epithelial physiology
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Mitochondrial Ca2+ Transport in Frog Early Distal Tubule
Mark R Fowler 1
Malcolm Hunter 1*
1 University of Leeds
* To whom correspondence should be addressed. E-mail: m.hunter{at}leeds.ac.uk.
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Abstract |
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A global and transient rise of intracellular Ca2+ (Ca2+i) is central to the operation of pump-leak coupling in the frog Early Distal Tubule (EDT). The ER is the site of this Ca2+ release and reuptake; however it is likely that other intracellular pools such as mitochondria also contribute to cellular Ca2+ homeostasis. The current study was performed to seek evidence of mitochondrial Ca2+ transport in the frog EDT. Experiments were performed on isolated and permeabilised EDT segments from the frog kidney loaded with the low affinity, Ca2+-sensitive fluorescent indicator, mag-fura-2. Ca2+ uptake in the absence of SERCA activity (inhibition by TBQ) was evident at a bath [Ca2+] of 1 mM, but not at 200 nM, in the presence of ATP. This uptake was sensitive to the protonophore FCCP and the ATP-synthase inhibitor oligomycin. Ca2+ uptake was also stimulated by respiratory substrates; this uptake was enhanced by oligomycin and reversed by the application of FCCP. These findings provide the first evidence of mitochondrial Ca2+ transport in renal tubules, which appears to occur via a low-affinity pathway and which will act as a physiological Ca2+ buffer, protecting the cell from large increases in Ca2+i.
Key Words:
Calcium, Kidney, Mitochondria
