title: Effect of sodium and sodium-substitutes on the active ion transport and on the membrane potential of smooth muscle cells.
abstract: 1. The changes of the ion content and of the membrane potential of taenia coli cells have been studied during prolonged exposure to Na-deficient solutions containing either Li or choline.2. A K-free solution containing either 71 mM-Na-71 mM-Li or 71 mM-Na-71 mM choline causes a slower loss of cellular K than a 142 mM-Na solution. In both these Na-deficient solutions the membrane hyperpolarizes to about -100 mV for periods up to 6 hr. This hyperpolarization is partially abolished by 2 x 10(-5)M ouabain.3. Replacing all extracellular Na by Li and maintaining 5.9 mM-K causes a fast loss of all Na and a progressive replacement of K by Li. These changes of the intracellular ion content are accompanied by a depolarization of the cells, suggesting that intracellular Li cannot substitute for Na in activating the ion pump.4. Exposing K-depleted cells to a K-free 71 mM-Na-71 mM-Li solution results in a ouabain sensitive transport of Na and Li against their electro-chemical gradient.5. The K-uptake by K-depleted cells from a solution containing 0.59 mM-K is increased by reducing [Na](o) to half of its normal value. This finding indicates that external Na inhibits the active Na-K exchange.6. In Na-enriched tissues half of the Na efflux is due to a ouabain insensitive Na-exchange diffusion. If Li is used as a Na substitute, the Na-Li exchange compensates for the diminution of the Na-exchange diffusion unless ouabain is added.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects*; D002794:Choline / Q000494:pharmacology*; D003106:Colon / Q000378:metabolism / Q000502:physiology; D003864:Depression, Chemical; D004058:Diffusion; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008094:Lithium / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects*; D009130:Muscle, Smooth / Q000378:metabolism / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D010042:Ouabain; D008094:Lithium; D012964:Sodium; D002794:Choline; D011188:Potassium