title: Fluorescence measurement of intracellular sodium concentration in single Escherichia coli cells.
abstract: The energy-transducing cytoplasmic membrane of bacteria contains pumps and antiports maintaining the membrane potential and ion gradients. We have developed a method for rapid, single-cell measurement of the internal sodium concentration ([Na(+)](in)) in Escherichia coli using the sodium ion fluorescence indicator, Sodium Green. The bacterial flagellar motor is a molecular machine that couples the transmembrane flow of ions, either protons (H(+)) or sodium ions (Na(+)), to flagellar rotation. We used an E. coli strain containing a chimeric flagellar motor with H(+)- and Na(+)-driven components that functions as a sodium motor. Changing external sodium concentration ([Na(+)](ex)) in the range 1-85 mM resulted in changes in [Na(+)](in) between 5-14 mM, indicating a partial homeostasis of internal sodium concentration. There were significant intercell variations in the relationship between [Na(+)](in) and [Na(+)](ex), and the internal sodium concentration in cells not expressing chimeric flagellar motors was 2-3 times lower, indicating that the sodium flux through these motors is a significant fraction of the total sodium flux into the cell.
authors.affiliation: Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom.
authors.forename: Chien-Jung
authors.initials: CJ
authors.lastname: Lo
authors.forename: Mark C
authors.initials: MC
authors.lastname: Leake
authors.forename: Richard M
authors.initials: RM
authors.lastname: Berry
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry; D002138:Calibration; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000737:chemistry; D006096:Gramicidin / Q000494:pharmacology; D008027:Light; D008856:Microscopy, Fluorescence / Q000379:methods*; D009930:Organic Chemicals / Q000737:chemistry / Q000494:pharmacology; D038761:Photobleaching; D010957:Plasmids / Q000378:metabolism; D011522:Protons; D012964:Sodium / Q000737:chemistry; D013997:Time Factors
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D005456:Fluorescent Dyes; D009930:Organic Chemicals; D011522:Protons; C098118:sodium green; D006096:Gramicidin; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D012964:Sodium