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It is now known that sodium and potassium ions exchange rapidly between cells and body fluids, and that the observed concentration gradients are not due to impermeability of the cell membrane (see reviews by It is also known that the production and maintenance of physiological concentration gradients of sodium and potassium in isolated kidney-cortex slices require respiratory energy (Krebs, Eggleston & Terner, 1951; Mudge, 1951a, b; Aebi, 1953; WAhittam & Davies, 1953b).
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Whittam et al. (1954) studied this question.
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