A comparison of Zn2+- and Ca2+-triggered depolarization of liver mitochondria reveals no evidence of Zn2+-induced permeability transition.
Intracellular Zn(2+) toxicity is associated with mitochondrial dysfunction. Zn(2+) depolarizes mitochondria in assays using isolated organelles as well as cultured cells. Some reports suggest that Zn(2+)-induced depolarization results from the opening of the mitochondrial permeability transition pore (mPTP). For a more detailed analysis of this relationship, we compared Zn(2+)-induced depolarization with the effects of Ca(2+) in single isolated rat liver mitochondria monitored with the potentiometric probe rhodamine 123. Consistent with previous work, we found that relatively low levels of Ca(2+) caused rapid, complete and irreversible loss of mitochondrial membrane potential, an effect that was diminished by classic inhibitors of mPT, including high Mg(2+), ADP and cyclosporine A. Zn(2+) also depolarized mitochondria, but only at relatively high concentrations. Furthermore Zn(2+)-induced depolarization was slower, partial and sometimes reversible, and was not affected by inhibitors of mPT. We also compared the effects of Ca(2+) and Zn(2+) in a calcein-retention assay. Consistent with the well-documented ability of Ca(2+) to induce mPT, we found that it caused rapid and substantial loss of matrix calcein. In contrast, calcein remained in Zn(2+)-treated mitochondria. Considered together, our results suggest that Ca(2+) and Zn(2+) depolarize mitochondria by considerably different mechanisms, that opening of the mPTP is not a direct consequence of Zn(2+)-induced depolarization, and that Zn(2+) is not a particularly potent mitochondrial inhibitor.
Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA 15261, USA.
Michael J
MJ
Devinney
Latha M
LM
Malaiyandi
Olga
O
Vergun
Donald B
DB
DeFranco
Teresa G
TG
Hastings
Kirk E
KE
Dineley
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005452:Fluoresceins / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D053078:Membrane Potential, Mitochondrial / Q000502:physiology*; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins / Q000378:metabolism*; D000083162:Mitochondrial Permeability Transition Pore; D010539:Permeability; D051381:Rats; D017207:Rats, Sprague-Dawley; D020112:Rhodamine 123 / Q000378:metabolism; D012430:Ruthenium Red / Q000378:metabolism; D015032:Zinc / Q000378:metabolism*
D027682:Cation Transport Proteins; D004791:Enzyme Inhibitors; D005452:Fluoresceins; D005456:Fluorescent Dyes; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D012430:Ruthenium Red; D020112:Rhodamine 123; D016572:Cyclosporine; D015032:Zinc; D002118:Calcium; C007740:fluorexon