Effects of water content upon the respiration and the cations of kidney slices.

1. Cortical slices from the kidneys of adult rats were incubated aerobically at 38.5 degrees C in Warburg manometers in an ordinary balanced saline medium and also in ;low-ion' media consisting of 20 mM Tris buffer to which 0-30 g polyethylene glycol (;PEG 6000')/100 ml. was added to control the swelling of the tissue.2. Oxygen uptake in the low ion media containing less than 2 m-equiv/l. of Na(+) and K(+) was maximal when the water content of the slices was kept normal by 14% PEG 6000 in the medium, and was about two thirds of the oxygen consumption in a balanced saline medium.3. Slices respiring in the low-ion media retained potassium in concentrations 10-20 times the concentration in the medium; the ratio of tissue to external concentration of K(+) was inversely related to the water content of the tissue.4. Ratios of K(+)/Na(+) concentration in tissue water were maximal and equal to 10-25 when water content was near normal and the ratio Na(+)/K(+) in the medium was between 1.5 and 2.0.5. Cryoscopic measurements showed that 14% of PEG 6000 contributed 140 m-osmole/kg to the osmolality of the low-ion media in which slices maintained a normal water content.6. It was not possible to interpret the volume of the cells as determined by the balance between the osmotic effect of PEG 6000 in the medium and the colloid osmotic pressure of intracellular proteins.