title: Sodium, potassium, two chloride cotransport in corneal endothelium: characterization and possible role in volume regulation and fluid transport.
abstract: OBJECTIVE
  To search for membrane transporter proteins that could contribute to volume regulation and fluid transport by corneal endothelium. As an initial step, the authors have focused on Na+-K+-2Cl- cotransporters.
  
  
  METHODS
  Bovine corneal endothelial cells were cultured to confluence. 86Rubidium was used as a tracer for K+ uptake determinations; uptake values were normalized per milligram of cell protein.
  
  
  RESULTS
  Three components of K+ uptake were characterized: ouabain (1 mM) sensitive, bumetanide (0.1 mM) sensitive, and ouabain-bumetanide insensitive. Both the ouabain-sensitive and bumetanide-sensitive components increased in the presence of 26.2 mM HCO3-; 0.5 mM 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid abolished this increase. The bumetanide-sensitive component was completely inhibited in the absence of Na+ or Cl-. This component was increased 33% by a 33% hypertonic solution and was decreased 38% by a 33% hypotonic solution. The protein kinase C activator phorbol 12-myristate 13-acetate decreased the activity of the cotransporter, whereas forskolin, in the presence of isobutylmethylxanthine, decreased it. Calyculin A (100 nM), an inhibitor of phosphatases 1 and 2a, produced a large (97%) activation of this component.
  
  
  CONCLUSIONS
  These results provided for the first time conclusive evidence for the presence of a Na+-K+-2Cl- cotransporter in corneal endothelium and of its possible involvement in volume-regulatory processes in these cells. Given the uptake values reported here, such cotransporter could contribute significantly to electrolyte transport and hence to fluid transport across this preparation.
authors.affiliation: Department of Physiology, College of Physicians and Surgeons, Columbia University, New York, New York, USA.
authors.forename: F P
authors.initials: FP
authors.lastname: Diecke
authors.forename: Z
authors.initials: Z
authors.lastname: Zhu
authors.forename: F
authors.initials: F
authors.lastname: Kang
authors.forename: K
authors.initials: K
authors.lastname: Kuang
authors.forename: J
authors.initials: J
authors.lastname: Fischbarg
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002034:Bumetanide / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002417:Cattle; D048429:Cell Size / Q000502:physiology; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004728:Endothelium, Corneal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D028021:Sodium-Potassium-Chloride Symporters; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D002712:Chlorides; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; D028021:Sodium-Potassium-Chloride Symporters; D002034:Bumetanide; D005576:Colforsin; D010042:Ouabain; D012964:Sodium; D013755:Tetradecanoylphorbol Acetate; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D011188:Potassium; D015056:1-Methyl-3-isobutylxanthine