Boelens 2013 J Bioenerg Biomembr

Boelens AD, Pradhan RK, Blomeyer CA, Camara AK, Dash RK, Stowe DF (2013) Extra-matrix Mg2+ limits Ca2+ uptake and modulates Ca2+ uptake-independent respiration and redox state in cardiac isolated mitochondria. J Bioenerg Biomembr 45:203-18.

» PMID: 23456198 Open Access

Boelens AD, Pradhan RK, Blomeyer CA, Camara AK, Dash RK, Stowe DF (2013) J Bioenerg Biomembr

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 (ΔΨm), 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. • Keywords: Cardiac mitochondria, Inner mitochondrial membrane, Bioenergetics, Ca²⁺ uniporter, Ca²⁺ uptake, Mg²⁺ inhibition

• O2k-Network Lab: US WI Milwaukee Dash RK

Labels: MiParea: Respiration 

Organism: Guinea pig  Tissue;cell: Heart  Preparation: Isolated mitochondria 

Regulation: Calcium, Redox state  Coupling state: LEAK, OXPHOS  Pathway: N  HRR: Oxygraph-2k