Mitochondrial Ca2+ transport in frog early distal tubule.
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 endoplasmic reticulum (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 present study was performed to seek evidence of mitochondrial Ca2+ transport in the frog EDT. Experiments were performed on isolated and permeabilized EDT segments from the frog kidney loaded with the low-affinity, Ca2+-sensitive fluorescent indicator, mag-fura-2. Ca2+ uptake in the absence of SarcoEndoplasmic Reticulum Calcium ATPase (SERCA) activity (inhibition by 2,5-di-t-butyl hydroquinone, TBQ) was evident at a bath [Ca2+] of 1 microm, 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.
Fowler
Mark R
MR
School of Biomedical Sciences, Worsley Building, University of Leeds, Leeds, LS2 9NQ, UK.
Hunter
Malcolm
M
D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004579:Electron Transport / Q000502:physiology; D007686:Kidney Tubules, Distal / Q000502:physiology*; D008928:Mitochondria / Q000502:physiology*; D011896:Rana temporaria
D002118:Calcium