title: Chloride homeostasis in Saccharomyces cerevisiae: high affinity influx, V-ATPase-dependent sequestration, and identification of a candidate Cl- sensor.
abstract: Chloride homeostasis in Saccharomyces cerevisiae has been characterized with the goal of identifying new Cl- transport and regulatory pathways. Steady-state cellular Cl- contents ( approximately 0.2 mEq/liter cell water) differ by less than threefold in yeast grown in media containing 0.003-5 mM Cl-. Therefore, yeast have a potent mechanism for maintaining constant cellular Cl- over a wide range of extracellular Cl-. The cell water:medium [Cl-] ratio is >20 in media containing 0.01 mM Cl- and results in part from sequestration of Cl- in organelles, as shown by the effect of deleting genes involved in vacuolar acidification. Organellar sequestration cannot account entirely for the Cl- accumulation, however, because the cell water:medium [Cl-] ratio in low Cl- medium is approximately 10 at extracellular pH 4.0 even in vma1 yeast, which lack the vacuolar H(+)-ATPase. Cellular Cl- accumulation is ATP dependent in both wild type and vma1 strains. The initial (36)Cl- influx is a saturable function of extracellular [(36)Cl-] with K(1/2) of 0.02 mM at pH 4.0 and >0.2 mM at pH 7, indicating the presence of a high affinity Cl- transporter in the plasma membrane. The transporter can exchange (36)Cl- for either Cl- or Br- far more rapidly than SO4=, phosphate, formate, HCO3-, or NO3-. High affinity Cl- influx is not affected by deletion of any of several genes for possible Cl- transporters. The high affinity Cl- transporter is activated over a period of approximately 45 min after shifting cells from high-Cl- to low-Cl- media. Deletion of ORF YHL008c (formate-nitrite transporter family) strongly reduces the rate of activation of the flux. Therefore, Yhl008cp may be part of a Cl(-)-sensing mechanism that activates the high affinity transporter in a low Cl- medium. This is the first example of a biological system that can regulate cellular Cl- at concentrations far below 1 mM.
authors: Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA. JenningsMichaelL@uams.edu
authors: Michael L
authors: ML
authors: Jennings
authors: Jian
authors: J
authors: Cui
mesh_terms: D001639:Bicarbonates / Q000378:metabolism; D001693:Biological Transport, Active / Q000502:physiology; D001965:Bromides / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002712:Chlorides / Q000737:chemistry / Q000378:metabolism*; D003470:Culture Media; D006706:Homeostasis / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008024:Ligands; D009566:Nitrates / Q000378:metabolism; D009994:Osmolar Concentration; D011868:Radioisotopes; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism; D017384:Sequence Deletion; D013447:Sulfites / Q000378:metabolism; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism*; D014617:Vacuoles / Q000378:metabolism
chemical_list: D001639:Bicarbonates; D001965:Bromides; D002712:Chlorides; D003470:Culture Media; D008024:Ligands; D009566:Nitrates; D011868:Radioisotopes; D029701:Saccharomyces cerevisiae Proteins; D013447:Sulfites; D025262:Vacuolar Proton-Translocating ATPases