title: The microaerophilic flagellate Giardia intestinalis: oxygen and its reaction products collapse membrane potential and cause cytotoxicity.
abstract: Trophozoites of the microaerophilic flagellate parasitic protozoon Giardia intestinalis have only a limited capacity to detoxify O(2). Thus, when exposed to controlled concentrations of dissolved O(2) >8 microM, they gradually lose their ability to scavenge O(2). In a washed cell suspension stirred under 10% air in N(2) (equivalent to 25 microM O(2)), inactivation of the O(2)-consuming system was complete after 3.5 h; during this period accumulation of H(2)O(2) (3 micromol per 10(6) organisms) and oxidation of cellular thiols to 16% of their initial level occurred. Under 20% air (50 microM O(2)), respiratory inactivation was complete after 1.5 h, and under air (258 microM O(2)), after 50 min. Loss of O(2)-consuming capacity was accompanied by loss of motility. Use of the fluorogen 2, 7-dichlorodihydrofluorescein acetate indicated that intracellular H(2)O(2) is produced at extranuclear sites. Flow cytometric estimation of the plasma membrane electrochemical potentials using bis(1,3-dibutylbarbituric acid) trimethine oxonol, DiBAC(4)(3), showed that values declined from -134 mV to -20 mV after 4.5 h aeration. Incubation of organisms with 60 microM H(2)O(2) for 10 min gave partial collapse of plasma membrane potential and complete loss of O(2) uptake capacity; motility and viability as assessed by DiBAC(4)(3) exclusion were completely lost after 1 h. Inactivation of the O(2)-consuming system and loss of viability were also observed on exposure to singlet oxygen photochemically generated from rose bengal or toluidine blue.
authors: Microbiology Group, School of Biosciences (BIOSI, Main Building), Cardiff University, Cardiff CF10 3TL, UK2.
authors: David
authors: D
authors: Lloyd
authors: Microbiology Group, School of Biosciences (BIOSI, Main Building), Cardiff University, Cardiff CF10 3TL, UK2.
authors: Janine C
authors: JC
authors: Harris
authors: School of Biochemistry and Molecular Genetics and Cellular Analysis Facility, School of Microbiology and Immunology, University of New South Wales, Kensington, Sydney 2052, Australia1.
authors: Sarah
authors: S
authors: Maroulis
authors: School of Biochemistry and Molecular Genetics and Cellular Analysis Facility, School of Microbiology and Immunology, University of New South Wales, Kensington, Sydney 2052, Australia1.
authors: Giancarlo A
authors: GA
authors: Biagini
authors: School of Biochemistry and Molecular Genetics and Cellular Analysis Facility, School of Microbiology and Immunology, University of New South Wales, Kensington, Sydney 2052, Australia1.
authors: Robert B
authors: RB
authors: Wadley
authors: Microbiology Group, School of Biosciences (BIOSI, Main Building), Cardiff University, Cardiff CF10 3TL, UK2.
authors: Michael P
authors: MP
authors: Turner
authors: School of Biochemistry and Molecular Genetics and Cellular Analysis Facility, School of Microbiology and Immunology, University of New South Wales, Kensington, Sydney 2052, Australia1.
authors: Michael R
authors: MR
authors: Edwards
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000502:physiology; D005434:Flow Cytometry; D016829:Giardia lamblia / Q000254:growth & development / Q000502:physiology* / Q000648:ultrastructure; D006861:Hydrogen Peroxide / Q000378:metabolism; D008564:Membrane Potentials; D008854:Microscopy, Electron; D018384:Oxidative Stress; D010100:Oxygen / Q000494:pharmacology* / Q000633:toxicity; D010101:Oxygen Consumption; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D017382:Reactive Oxygen Species; D006861:Hydrogen Peroxide; D010100:Oxygen