Demonstration of an electrogenic Na+-K+ pump in mouse spleen macrophages.
The effect of ouabain on the membrane potential of cultured mouse spleen macrophages was examined. Ouabain (10(-3) M) induced a membrane depolarization (6.6 mV) in 18 of 19 cells studied that occurred within several minutes after exposure and was not associated with significant changes in current-voltage relationships. In related studies, cells were placed in K+-free medium in the cold for 2 h to block pump activity. Subsequent exposure to K+ at 37 degrees C resulted in a membrane hyperpolarization. However, addition of K+ also enhanced inward rectification. To differentiate between the effect of K+ on the Na+-K+ pump and its action on inward rectification, two types of experiments were done. Studies performed in the presence of barium, which blocks inward rectification, demonstrated a K+-induced hyperpolarization with no changes in rectification. Additional studies examined the effects of rubidium on Na+-loaded cells. Rubidium, which blocks inward rectification but substitutes for K+ in activating the Na+-K+ pump, induced membrane hyperpolarizations that were reversed by addition of ouabain. These data indicate that macrophages exhibit an electrogenic Na+-K+ pump, which probably contributes to the resting membrane potential under steady-state conditions and can be activated under conditions designed to Na+ load the cells. In addition, they demonstrate that increasing extracellular K+ enhances inward rectification in macrophages.
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D007700:Kinetics; D008264:Macrophages / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008815:Mice, Inbred Strains; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013154:Spleen / Q000502:physiology*
D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium