title: Foreign anions modulate volume set point of sheep erythrocyte K-Cl cotransport.
abstract: Preequilibration at 37 degrees C in isosmotic media with Cl replaced by lyotropic (foreign) anions reversibly increased Cl-dependent K efflux and Rb influx, the inhibition by furosemide, and thus K-Cl cotransport in low-K but not in high-K sheep erythrocytes with the following order of effectiveness: SCN greater than I greater than NO3 greater than Cl = Br. This effect depended on time, temperature, and anion concentration and was reversible. Preincubation in isosmotic SCN at 37 degrees C stimulated K-Cl flux in anisosmotic Cl media (370-240 mosM) by increasing the volume sensitivity through shifting the point of zero K-Cl flux by approximately 100 mosmol. Thus even shrunken cells exhibited K-Cl cotransport. Preincubation in hyperosmotic SCN or Cl (440 mosM) followed by K flux in hyposmotic Cl (240 mosM) caused a 30-min lag phase that was absent when cells were swollen only. Hence, foreign anions increased the K flux rate in Cl, suggesting upregulation of K-Cl cotransport through new sites or higher turnover per transporter. The anions must act directly on proteins and/or lipids as the accompanying intracellular pH (pHi) changes were too small to attribute the K-Cl flux activation to cellular acidification. After thiol alkylation, which also activates K-Cl cotransport, SCN preexposure at 37 degrees C became ineffective. Carbethoxylation significantly reduced the foreign anion enhancement of K-Cl cotransport and abolished K efflux in Br. It is concluded that interaction of anions through carbethoxylation-sensitive sites with thiols may determine the level of K-Cl cotransport activity.
authors.affiliation: Department of Physiology and Biophysics, Wright State University, Dayton, Ohio 45401-0927.
authors.forename: P K
authors.initials: PK
authors.lastname: Lauf
mesh_terms: D000818:Animals; D000838:Anions; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000097:blood*; D002712:Chlorides / Q000097:blood*; D004912:Erythrocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005665:Furosemide / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000097:blood*; D012413:Rubidium; D012756:Sheep; D027981:Symporters; D013696:Temperature; D000096922:K Cl- Cotransporters
chemical_list: D000838:Anions; D002352:Carrier Proteins; D002712:Chlorides; D005665:Furosemide; D010042:Ouabain; D011188:Potassium; D012413:Rubidium; D027981:Symporters; D000096922:K Cl- Cotransporters