Extra-matrix Mg²⁺ Limits Ca²⁺ Uptake and Modulates Ca²⁺ Uptake-independent Respiration and Redox State in Cardiac Isolated Mitochondria

Authors

Age D. Boelens, Medical College of Wisconsin
Ranjan K. Pradhan, Medical College of Wisconsin
Christoph A. Blomeyer, Medical College of Wisconsin
Amadou K.S. Camara, Medical College of Wisconsin
Ranjan K. Dash, Medical College of Wisconsin
David F. Stowe, Marquette University

Document Type

Article

Language

eng

Format of Original

16 p.

Publication Date

6-2013

Publisher

Springer Verlag

Source Publication

Journal of Bioenergetics and Biomembranes

Source ISSN

0145-479X

Original Item ID

doi: 10.1007/s10863-013-9500-5

Abstract

Cardiac mitochondrial matrix (m) free Ca²⁺ ([Ca²⁺]_m) increases primarily by Ca²⁺ uptake through the Ca²⁺ uniporter (CU). Ca²⁺ uptake via the CU is attenuated by extra-matrix (e) Mg²⁺ ([Mg²⁺]_e). How [Ca²⁺]_m is dynamically modulated by interacting physiological levels of [Ca²⁺]_e and [Mg²⁺]_e and how this interaction alters bioenergetics are not well understood. We postulated that as [Mg²⁺]_e modulates Ca²⁺ uptake via the CU, it also alters bioenergetics in a matrix Ca²⁺–induced and matrix Ca²⁺–independent manner. To test this, we measured changes in [Ca²⁺]_e, [Ca²⁺]_m, [Mg²⁺]_e and [Mg²⁺]_m spectrofluorometrically in guinea pig cardiac mitochondria in response to added CaCl₂ (0–0.6 mM; 1 mM EGTA buffer) with/without added MgCl₂ (0–2 mM). In parallel, we assessed effects of added CaCl₂ and MgCl₂ on NADH, membrane potential (ΔΨ_m), and respiration. We found that >0.125 mM MgCl₂ significantly attenuated CU-mediated Ca²⁺ uptake and [Ca²⁺]_m. Incremental [Mg²⁺]_e did not reduce initial Ca²⁺uptake but attenuated the subsequent slower Ca²⁺ uptake, so that [Ca²⁺]_m remained unaltered over time. Adding CaCl₂ without MgCl₂ to attain a [Ca²⁺]_m from 46 to 221 nM enhanced state 3 NADH oxidation and increased respiration by 15 %; up to 868 nM [Ca²⁺]_m did not additionally enhance NADH oxidation or respiration. Adding MgCl₂ did not increase [Mg²⁺]_m but it altered bioenergetics by its direct effect to decrease Ca²⁺ uptake. However, at a given [Ca²⁺]_m, state 3 respiration was incrementally attenuated, and state 4 respiration enhanced, by higher [Mg²⁺]_e. Thus, [Mg²⁺]_e without a change in [Mg²⁺]_m can modulate bioenergetics independently of CU-mediated Ca²⁺ transport.

Comments

Accepted version. Journal of Bioenergetics and Biomembranes, Vol. 45, No. 3 (June 2013): 203-218. DOI. © 2013 Springer Verlag. Used with permission.

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Recommended Citation

Boelens, Age D.; Pradhan, Ranjan K.; Blomeyer, Christoph A.; Camara, Amadou K.S.; Dash, Ranjan K.; and Stowe, David F., "Extra-matrix Mg²⁺ Limits Ca²⁺ Uptake and Modulates Ca²⁺ Uptake-independent Respiration and Redox State in Cardiac Isolated Mitochondria" (2013). Biomedical Engineering Faculty Research and Publications. 329.
https://epublications.marquette.edu/bioengin_fac/329