INHIBITION OF NA+-K+ PUMP ACTIVITY BY DIVALENT-CATIONS IN INTACT PERITONEAL MAST-CELLS OF THE RAT

1. The inhibition by the divalent cations magnesium, barium and strontium and the trivalent ion lanthanum of the Na+-K+ pump in the plasma membrane of rat peritoneal mast cells was studied in pure mast cell populations by measurement of the ouabain-sensitive uptake of the radioactive potassium analogue, 86rubidium (86Rb+). 2. Exposure of the cells to magnesium induced a time- and concentration-dependent decrease in the ouabain-sensitive K+ (86Rb+)-uptake of the cells without influencing the ouabain-resistant uptake. The time-dependent decrease was apparent after incubation of the cells for 10 min or more, but no decrease was observed after 2 min incubation when the cells are supposed to be loaded with sodium due to the cell isolation procedure. 3. Barium and strontium caused concentration-dependent decreases in the ouabain-sensitive K+(86Rb+)-uptake of the cells but the ouebain-resistant uptake was not changed. Half maximum decrease in the ouebain-sensitive K+(86Rb+)-uptake was observed with 1.8 mM magnesium, 1.2 mM barium and 0.7 mM strontium. 4. The trivalent ion lanthanum blocked completely the ouabain-sensitive K+(86Rb+)-uptake at a concentration of 1 μM as does 1 mM calcium. Combining either of these ions with magnesium had no further inhibitory effect on the ouabain-sensitive uptake. 5. In conclusion, in addition to the previously suggested modulation by calcium of the activity of the Na+-K+ pump, evidence is provided in this investigation that the modulation may be a more general effect of divalent and polyvalent cations present in the extracellular space through their influence on the sodium permeability of the plasma membrane.