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Reduced mitochondrial volume contributes but cannot fully explain the increase in matrix free calcium after addition of ADP
Author(s) -
Boelens Age Douwe,
Stowe David F,
Aldakkak Mohammed,
Gadicherla Ashish K,
Dash Ranjan K,
Haumann Johan,
Camara Amadou K S
Publication year - 2010
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.24.1_supplement.1048.9
Subject(s) - mitochondrial matrix , mitochondrion , chemistry , egta , contraction (grammar) , biophysics , calcium , matrix (chemical analysis) , atp–adp translocase , volume (thermodynamics) , bioenergetics , biochemistry , inner mitochondrial membrane , cytosol , biology , chromatography , endocrinology , enzyme , physics , organic chemistry , quantum mechanics
In an earlier study we showed a transient doubling of mitochondrial matrix (m) [Ca 2+ ] in response to added ADP and proposed that greater buffering of Ca 2+ by ATP than by ADP is largely responsible for the increase. Previous studies have described mitochondrial volume contraction in response to ADP. Thus we explored if reduced mitochondrial volume with ADP also contributes to the apparent increase in m[Ca 2+ ]. Guinea pig heart mitochondria were isolated by differential centrifugation. Mitochondria were suspended in respiration media, including 1 mM EGTA, 1 mM MgCl 2 , 140 mM KCl, and 5 mM K 2 HPO 4 . Mitochondria were energized with pyruvic acid followed by 250 μM ADP. Mitochondrial volume was measured by light scattering at a wavelength of 520 nm. Alamethicin (5 μg/ml) was added at the end to attain maximal matrix volume. Changes in matrix volume after addition of ADP were calculated as a percentage of maximal volume change. We showed a matrix contraction in response to ADP of approximately 5% of the maximal change in matrix volume. We conclude that although matrix contraction can contribute to the increase in [Ca 2+ ] after addition of ADP, it explains only a small proportion of the rise in [Ca 2+ ] during phosphorylation of ADP, suggesting differential Ca 2+ buffering of ADP and ATP remains a major factor.