title: Perturbation of intracellular K(+) homeostasis with valinomycin promotes cell death by mitochondrial swelling and autophagic processes.
abstract: Perturbation of cellular K(+) homeostasis is a common motif in apoptosis but it is unknown whether a decrease in intracellular K(+) alone is sufficient to replicate apoptotic hallmarks. We investigated, which mode of cell death is induced by decreasing the intracellular K(+) concentration using valinomycin, a highly K(+)-selective ionophore. Valinomycin treatment induced mitochondrial swelling and minor nuclear changes in cell lines (BV-2, C6, HEK 293), and in primary mouse microglia and astrocytes. In the microglial cell line BV-2, we identified and quantified three phenotypes in valinomycin-exposed cells. The first and most prevalent phenotype (62 ± 2%) was characterized by swollen mitochondria and no chromatin condensation, and the second (25 ± 3%) by swollen mitochondria and slight chromatin condensation. Only the third phenotype (11 ± 4%) fulfilled criteria of apoptosis by having normal-sized mitochondria and strongly condensed chromatin. Valinomycin-induced swelling of mitochondria was not altered by the adenine nucleotide translocase inhibitor bongkrekic acid (BA), the pan caspase inhibitor Z-VAD-FMK, changing extracellular K(+) or Cl(-) concentrations, or the membrane-permeable Ca(2+) chelator BAPTA-AM. Only co-exposure of cells to valinomycin and the Ca(2+) ionophore ionomycin in high K(+) Cl(-)-free extracellular solution suppressed mitochondrial swelling. Ionomycin alone caused shrinkage of mitochondria. Additionally, valinomycin promoted autophagic processes, which were further enhanced by preincubation with BA or with Z-VAD-FMK. Valinomycin-dependent chromatin condensation was inhibited by BA, Z-VAD-FMK, BAPTA-AM, and ionomycin. Our findings demonstrate that mitochondrial swelling and autophagy are common features of valinomycin-exposed cells. Accordingly, valinomycin promotes an autophagic cell death mode, but not apoptosis.
authors.affiliation: Department of Cell Biology, University of Salzburg, Hellbrunnerstr. 34, 5020 Salzburg, Austria.
authors.forename: Barbara
authors.initials: B
authors.lastname: Klein
authors.forename: Katrin
authors.initials: K
authors.lastname: Wörndl
authors.forename: Ursula
authors.initials: U
authors.lastname: Lütz-Meindl
authors.forename: Hubert H
authors.initials: HH
authors.lastname: Kerschbaum
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D001343:Autophagy / Q000187:drug effects*; D002460:Cell Line; D002463:Cell Membrane Permeability / Q000187:drug effects; D042002:Chromatin Assembly and Disassembly / Q000187:drug effects; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D017136:Ion Transport / Q000187:drug effects*; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology*; D051379:Mice; D017628:Microglia / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D008933:Mitochondrial Swelling / Q000187:drug effects*; D010641:Phenotype; D011188:Potassium / Q000378:metabolism*; D061251:Primary Cell Culture; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D007476:Ionophores; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D014634:Valinomycin; D004533:Egtazic Acid; D015759:Ionomycin; D011188:Potassium