title: The role of pump number and intracellular sodium and potassium in determining Na,K pump activity in human erythrocytes.
abstract: The factors that determine the activity of the Na,K pump in vivo were investigated by measuring Na,K pump activity under in vivo conditions in human red cells and relating it to the intracellular content of sodium ([Na]i) and potassium ([K]i) and the number of pump units per cell (pump number). Na,K pump activity was measured as ouabain-sensitive K+ influx, pump number was determined from the maximal binding of 3H-ouabain to intact cells, and [Na]i and [K]i were measured by atomic absorption spectrophotometry in washed, packed cells. In the 81 samples studied, pump activity per cell was significantly correlated with pump number (r = .64, P less than 0.001), but was negatively correlated with [Na]i (r = -.28, P less than 0.02) and was not correlated with [K]i. An inverse relationship was found between pump number and [Na]i. When pump activity was expressed as activity per pump unit, rather than per cell, a significant relationship was seen between pump activity and [Na]i (r = .50, P less than 0.001), and a negative correlation existed between the activity per pump unit and [K]i (r = -.29, P less than 0.01). The effect of intracellular Na+ at physiologic levels on pump activity was not strong, with the activity per pump unit increasing only 25% with a doubling of [Na]i. These results indicate that pump number is the major determinant of pump activity in human red cells in vivo, while [Na]i and [K]i are of secondary importance.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D006801:Humans; D007700:Kinetics; D010042:Ouabain / Q000378:metabolism; D011188:Potassium / Q000097:blood*; D012964:Sodium / Q000097:blood*; D000254:Sodium-Potassium-Exchanging ATPase / Q000097:blood*; D013054:Spectrophotometry, Atomic
chemical_list: D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium