Mitochondrial Free [Ca²⁺] Increases during ATP/ADP Antiport and ADP Phosphorylation: Exploration of Mechanisms

Authors

Johan Haumann, Medical College of Wisconsin
Ranjan K. Dash, Medical College of Wisconsin
David F. Stowe, Marquette University
Age D. Boelens, Medical College of Wisconsin
Daniel A. Beard, Medical College of Wisconsin
Amadou K.S. Camara, Medical College of Wisconsin

Document Type

Article

Language

eng

Publication Date

8-2010

Publisher

Elsevier

Source Publication

Biophysical Journal

Source ISSN

0006-3495

Original Item ID

DOI: 10.1016/j.bpj.2010.04.069

Abstract

ADP influx and ADP phosphorylation may alter mitochondrial free [Ca²⁺] ([Ca²⁺]_m) and consequently mitochondrial bioenergetics by several postulated mechanisms. We tested how [Ca²⁺]_m is affected by H₂PO₄⁻ (P_i), Mg²⁺, calcium uniporter activity, matrix volume changes, and the bioenergetic state. We measured [Ca²⁺]_m, membrane potential, redox state, matrix volume, pH_m, and O₂ consumption in guinea pig heart mitochondria with or without ruthenium red, carboxyatractyloside, or oligomycin, and at several levels of Mg²⁺ and P_i. Energized mitochondria showed a dose-dependent increase in [Ca²⁺]_m after adding CaCl₂ equivalent to 20, 114, and 485 nM extramatrix free [Ca²⁺] ([Ca²⁺]_e); this uptake was attenuated at higher buffer Mg²⁺. Adding ADP transiently increased [Ca²⁺]_m up to twofold. The ADP effect on increasing [Ca²⁺]_m could be partially attributed to matrix contraction, but was little affected by ruthenium red or changes in Mg²⁺ or P_i. Oligomycin largely reduced the increase in [Ca²⁺]_m by ADP compared to control, and [Ca²⁺]_m did not return to baseline. Carboxyatractyloside prevented the ADP-induced [Ca²⁺]_m increase. Adding CaCl₂ had no effect on bioenergetics, except for a small increase in state 2 and state 4 respiration at 485 nM [Ca²⁺]_e. These data suggest that matrix ADP influx and subsequent phosphorylation increase [Ca²⁺]_m largely due to the interaction of matrix Ca²⁺ with ATP, ADP, P_i, and cation buffering proteins in the matrix.

Comments

Published version. Biophysical Journal, Vol. 99, No. 4 (August 2010): 997-1006. DOI. © 2010 Elsevier (Cell Press). Used with permission.

Recommended Citation

Haumann, Johan; Dash, Ranjan K.; Stowe, David F.; Boelens, Age D.; Beard, Daniel A.; and Camara, Amadou K.S., "Mitochondrial Free [Ca²⁺] Increases during ATP/ADP Antiport and ADP Phosphorylation: Exploration of Mechanisms" (2010). Biomedical Engineering Faculty Research and Publications. 273.
https://epublications.marquette.edu/bioengin_fac/273