title: Mitochondrial free [Ca2+] increases during ATP/ADP antiport and ADP phosphorylation: exploration of mechanisms.
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.
authors: Anesthesiology Research Laboratories, Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
authors: Johan
authors: J
authors: Haumann
authors: Ranjan K
authors: RK
authors: Dash
authors: David F
authors: DF
authors: Stowe
authors: Age D
authors: AD
authors: Boelens
authors: Daniel A
authors: DA
authors: Beard
authors: Amadou K S
authors: AK
authors: Camara
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism* / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002021:Buffers; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D019069:Cell Respiration / Q000187:drug effects; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D017136:Ion Transport / Q000187:drug effects; D008274:Magnesium / Q000378:metabolism; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects; D010766:Phosphorylation / Q000187:drug effects; D012430:Ruthenium Red / Q000494:pharmacology
chemical_list: D002021:Buffers; D009243:NAD; D012430:Ruthenium Red; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D008274:Magnesium; D002118:Calcium