Control of water content of non-metabolizing kidney slices by sodium chloride and polyethylene glycol (PEG 6000).

1. Cortical slices from kidneys of adult rats were equilibrated for 24 and 48 hr in the refrigerator in solutions containing 5 mM-K, 2.5 mM-Ca and Mg, M/15 phosphate buffer (pH 7.4), 5 mM cyanide and iodoacetate with 5, 6, 7 and 8% polyethylene glycol (PEG 6000) and 77, 154, 308, 462 and 770 mM-NaCl.2. There were no consistent differences in water content between slices after 24 and after 48 hr.3. Slices contained more water when either the concentration of NaCl or that of PEG was reduced. The increase in water content induced by lowering the concentration of either was prevented by a higher concentration of the other.4. Water content was held constant at 3.25 kg.kg(-1) dry PEG-free tissue despite a fall in [NaCl] from 770 to 77 mM (more than 1200 m-osmole.kg(-1)) by increasing PEG from 5.1 to 7.7% corresponding to an increase of the order of 15 m-osmole.kg(-1).5. It is suggested that PEG 6000 was so much more effective than NaCl, osmole for osmole, because PEG 6000 acted as a non-penetrating solute, whereas NaCl penetrated the slices and reduced the ;Donnan excess' component of the intracellular colloid osmotic pressure so that this could be balanced by a smaller concentration of PEG.