Plasma membrane electron transport coupled to Na(+) extrusion in the halotolerant alga Dunaliella.
The halotolerant alga Dunaliella adapts to exceptionally high salinity and maintains low [Na(+)](in) at hypersaline solutions, suggesting that it possesses efficient mechanisms for regulating intracellular Na(+). In this work we examined the possibility that Na(+) export in Dunaliella is linked to a plasma membrane electron transport (redox) system. Na(+) extrusion was induced in Dunaliella cells by elevation of intracellular Na(+) with Na(+)-specific ionophores. Elevation of intracellular Na(+) was found to enhance the reduction of an extracellular electron acceptor ferricyanide (FeCN). The quinone analogs NQNO and dicumarol inhibited FeCN reduction and led to accumulation of Na(+) by inhibition of Na(+) extrusion. These inhibitors also diminished the plasma membrane potential in Dunaliella. Anaerobic conditions elevated, whereas FeCN partially decreased intracellular Na(+) content. Cellular NAD(P)H level decreased upon enhancement of plasma membrane electron transport. These results are consistent with the operation of an electrogenic NAD(P)H-driven redox system coupled to Na(+) extrusion in Dunaliella plasma membrane. We propose that redox-driven Na(+) extrusion and recycling in Dunaliella evolved as means of adaptation to hypersaline environments.
Department of Biological Chemistry, The Weizmann Institute of Science, 76100, Rehovot, Israel. bckatzad@wicc.weizmann.ac.il
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D002462:Cell Membrane / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004579:Electron Transport; D056890:Eukaryota / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D005295:Ferrocyanides / Q000737:chemistry / Q000494:pharmacology; D006912:Hydroxyquinolines / Q000494:pharmacology; D008564:Membrane Potentials; D008985:Monensin / Q000494:pharmacology; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D012964:Sodium / Q000378:metabolism*
D005295:Ferrocyanides; D006912:Hydroxyquinolines; C010494:nonyl-4-hydroxyquinoline-N-oxide; D009249:NADP; D008985:Monensin; D012964:Sodium