title: Ouabain-sensitive ion fluxes in the smooth muscle of the guinea-pig's taenia coli.
abstract: 1. Tissues with raised intracellular Na levels, produced by incubation in K-free media, were used throughout. The uptake of 42K by these Na-loaded tissues was followed for 10 min in the presence and absence of 1-37 X 10(-4) M ouabain, this being sufficient to inhibit Na pumping maximally. Subtraction of the uptake seen in the presence from that seen in the absence of ouabain gave estimates of the pumped ouabain-sensitive K uptake. 2. In Na-free (MgCl2) medium this depended on the [K]0 in a sigmoidal fashion with a half maximal [K]0 for activation of some 4mM. The maximal uptake of K was 3 m-mole/kg.min corresponding to a transmembrane flux of some 12-5 p-mole. cm-2.sec-1. 3. In the presence of Na the K activation curve became more obviously sigmoid and higher concentrations of K were needed to achieve a given active K influx. The results were well fitted by assuming that Na and K competed for two identical, non-interacting sites on the external pump face. 4. Addition of K during the efflux of 24Na into a Na-free (MgCl2) medium led to an increased rate of tracer loss. The magnitude of this increase depended on the [K] used in a hyperbolic fashion and it was abolished by addition of ouabain. The [K] causing half-maximal activation of ouabain-sensitive Na efflux was in the order of 1-2 mM. 5. When the [K] in the uptake media was 1-5 mM; Na, Li, Rb and Cs all inhibited ouabain-sensitive K uptake, the order of effectiveness being Rb greater than Cs greater than Na greater than Li. With a E1TKA10 OF 0-15 MM low concentrations of Cs and Rb were shown to stimulate K uptake. Such an effect is predicted by assuming two ion binding sites on the pump's outer face, and that the pump can translocate mixtures of K and either Rb or Cs...
mesh_terms: D000818:Animals; D001665:Binding Sites; D001693:Biological Transport, Active / Q000187:drug effects; D002586:Cesium / Q000494:pharmacology; D003106:Colon / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008094:Lithium / Q000494:pharmacology; D008297:Male; D009130:Muscle, Smooth / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism*; D012413:Rubidium / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*
chemical_list: D002586:Cesium; D010042:Ouabain; D008094:Lithium; D012964:Sodium; D012413:Rubidium; D011188:Potassium