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Effect of sodium and sodium‐substitutes on the active ion transport and on the membrane potential of smooth muscle cells
Author(s) -
Casteels R.,
Droogmans G.,
Hendrickx H.
Publication year - 1973
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1973.sp010109
Subject(s) - ouabain , hyperpolarization (physics) , sodium , chemistry , depolarization , membrane potential , choline , biophysics , extracellular , intracellular , ion , ion transporter , membrane , membrane transport , biochemistry , stereochemistry , nuclear magnetic resonance spectroscopy , biology , organic chemistry
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 m M ‐Na‐71 m M ‐Li or 71 m M ‐Na‐71 m M choline causes a slower loss of cellular K than a 142 m M ‐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 × 10 −5 M ouabain. 3. Replacing all extracellular Na by Li and maintaining 5.9 m M ‐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 m M ‐Na‐71 m M ‐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 m M ‐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.