title: Na+-K+ pump activities of high- and low-potassium sheep red cells with internal magnesium and calcium altered by A23187.
abstract: 1. Sheep erythrocytes were treated with the divalent metal ionophore A23187 to alter the cellular magnesium (Mgi) and calcium (Cai) composition. Ouabain-sensitive Na+-K+ pump fluxes were measured using rubidium as a potassium congener in media where Cl- was replaced by NO3-. 2. A23187, per se, had no effect on ouabain-sensitive rubidium influx. However, lowering the concentration of cellular magnesium [( Mg]i) and increasing that of calcium [( Ca]i) decreased Na+-K+ pump flux. 3. Ouabain-sensitive rubidium influx was found to be a saturating function of [Mg]i in high-potassium (HK) red cells with a Hill coefficient of about 1.8 and an apparent half-activation constant (K0.5) of 0.46 mmol/(l original cells). In low-potassium (LK) cells, in the absence and presence of the Na+-K+ pump stimulatory L-antibody, ouabain-sensitive rubidium influx was also saturated with Mgi yielding Hill coefficients of close to 1.8 and K0.5 values of 0.20 and 0.30 mmol/(l original cells), respectively. 4. When [Ca]i was raised at constant [Mg]i ouabain-sensitive rubidium influx was inhibited at about 700 mumol/(l cells) in both HK, and in anti-L-treated LK red cells. 5. These data exclude the possibility that the Na+-K+ pump turnover, known to be different in HK red cells, and in LK red cells in the absence and presence of anti-L (Joiner & Lauf, 1978b), is based on differences in the activation by MgATP, and that Cai interacts with the Na+-K+ pump cycle differently in the two red cell cation types.
authors.affiliation: Department of Physiology and Biophysics, Wright State University, School of Medicine, Dayton, OH 45401.
authors.forename: H
authors.initials: H
authors.lastname: Fujise
authors.forename: P K
authors.initials: PK
authors.lastname: Lauf
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000097:blood*; D004912:Erythrocytes / Q000378:metabolism*; D008274:Magnesium / Q000097:blood*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000097:blood*; D012413:Rubidium / Q000097:blood; D012756:Sheep; D012964:Sodium / Q000097:blood*
chemical_list: D000001:Calcimycin; D010042:Ouabain; D012964:Sodium; D008274:Magnesium; D012413:Rubidium; D011188:Potassium; D002118:Calcium