Effects of impermeant medium ions on the composition of rabbit renal cortical slices

When incubated in isosmotic oxygenated medium in which chloride was completely replaced by gluconate, rabbit renal cortical slices lost chloride with sodium, potassium and water before reaching a new steady-state composition after 15-30 min. When corrected for extracellular space, there was an electroneutral loss of alkali metal cations (Na + K) with chloride, accompanied by isosmotic loss of water from the cells. The losses of chloride and water were independent of medium pH over the range of 6.4-8.2, and were the same with potassium rather than sodium as the dominant medium cation. Incubation in isosmotic sodium chloride medium restored tissue composition of slices transferred from gluconate medium. This recovery was not dependent specifically upon medium chloride, for slice water content also recovered when nitrate rather than chloride was substituted for medium gluconate. With sodium completely replaced by n-methyl d-glucamine (nmdG+), cells in slices lost far more sodium and potassium than chloride before reaching a new steady-state composition after some 30 min. However, the loss of water was as predicted from the total losses of measured inorganic ions. With sodium and chloride completely replaced by nmdG+ and gluconate, there was a greater loss of water than found with unilateral substitutions. Again, the combined loss of diffusible inorganic cations exceeded the loss of chloride but the water loss was that expected for isosmotic loss accompanying the measured losses of ions. These results reveal that both gluconate and nmdG+ behave as impermeant ions in this tissue preparation. It is suggested that, in the absence of medium sodium, sodium-hydrogen exchange is inhibited. Retained hydrogen ions are buffered on charged cellular non-diffusible solutes and the associated hydroxyl (or bicarbonate) ions are lost from the cells accompanied by the inorganic univalent cations lost in excess of chloride in nmdG+ medium.