Movements of Sodium, Potassium and Water in Rat Diaphragm in Vitro

¹ From the Department of Physiology, University of Western Ontario, London, Canada

Rat diaphragm was incubated for varying periods in Krebs-Ringer media of different osmolarities and in isotonic sucrose media under oxygen at 37°C and 0°C and under nitrogen at 37°C. The importance of metabolic activity on the regulation of water was reestablished for this tissue. In all conditions studied the movements of water were related to the distribution of Na and K. In isotonic media the water content was directly and linearly related to the sum of Na and K in the tissue: for every change of 35.2 mEq Na + K/kg dry weight there was a parallel movement of 1 gm water/100 gm of wet weight. Incubation in the sucrose media caused an immediate and continuous decrease in water under all metabolic conditions. This evidence indicates that the cell is isosmotic to its normal environment and that the regulation of water in diaphragm tissue is direct and passively related to the regulation of the normal tissue electrolytes, or to the distribution and regulation of the solutes present.