Resolution of the potassium ion pump in muscle fibers using barium ions.
When frog sartorius muscles recover from Na enrichment in the presence of external K, net K entry into the fibers occurs by both passive movement and active inward transport via a K pump. Under normal conditions, it has not been possible to experimentally distinguish these processes. Fractionation into the flux components must be accomplished from inferences concerning the K conductance or permeability during a period of rapid Na extrusion. The best estimates indicate that 60-80% of the K entry occurs via the K pump. In the presence of Ba ions, the membrane permeability to K is very much reduced. Under these conditions, Na-enriched muscles underwent a normal recovery in the presence of external K, and the amount of inward K movement due to the K pump rose to over 90% of the total K entry. The characteristics of the K pump studied by this means were: (a) essentially complete inhibition by 10(-4) M ouabain, (b) inhibition by [Na]omicron, (c) activation by [K]omicron according to a rectangular hyperbola in the absence of [Na]omicron, (d) linear activation by [Na]iota over a wide range in concentration, (e) zero or undetectably low pumping rate as [Na]iota leads to 0, (f) the number of Na ions actively transported per K ion actively transported is 1.4-1.7 normally and 1.1 in the presence of Ba.
D000818:Animals; D001001:Anura; D001464:Barium / Q000378:metabolism*; D002463:Cell Membrane Permeability; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009132:Muscles / Q000378:metabolism* / Q000502:physiology; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D011894:Rana pipiens; D012964:Sodium / Q000378:metabolism
D001464:Barium; D010042:Ouabain; D012964:Sodium; D011188:Potassium