Abstract
1. Thin diaphragm muscles in dialysed serum maintained their total sodium at values similar to those found in vivo. The fibre sodium exchanged with a half-time of 5 min, and the flux was 10 p-mole.cm-2.sec-1. The internal sodium was less than 10 μmoles/g fibre water and the ratio of external to internal sodium was at least 15. The calculated energy expenditure for sodium extrusion was less than 2% of the resting metabolism.