Electrolyte Composition of Mink (Mustela vison) Erythrocytes and Active Cation Transporters of the Cell Membrane

Red blood cells from mink (Mustela vison) were characterized with respect to their electrolyte content and their cell membranes with respect to enzymatic activity for cation transport. The intra- and extracellular concentrations of Na(+), K(+), Cl(-), Ca(2+ )and Mg(2+ )were determined in erythrocytes and plasma, respectively. Plasma and red cell water content was determined, and molal electrolyte concentrations were calculated. Red cells from male adult mink appeared to be of the low-K(+), high-Na(+ )type as seen in other carnivorous species. The intracellular K(+ )concentration is slightly higher than the extracellular one and the plasma-to-cell chemical gradient for Na(+ )is weak, though even the molal concentrations may differ significantly. Consistent with the high intracellular Na(+ )and low K(+ )concentrations, a very low or no ouabain-sensitive Na(+),K(+)-ATPase activity and no K(+)-activated pNPPase activity were found in the plasma membrane fraction from red cells. The Cl(- )and Mg(2+ )concentrations expressed per liter cell water were significantly higher in red cells than in plasma whereas the opposite was the case with Ca(2+). The distribution of Cl(- )thus does not seem compatible with an inside-negative membrane potential in mink erythrocytes. In spite of a steep calcium gradient across the red cell membrane, neither a calmodulin-activated Ca(2+)-ATPase activity nor an ATP-activated Ca(2+)-pNPPase activity were detectable in the plasma membrane fraction. The origin of a supposed primary Ca(2+ )gradient for sustaining of osmotic balance thus seems uncertain.