Effect of ionic substitutions on distal potential differences in rat kidney

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Abstract
Distal transtubular potential differences were measured in rat kidneys by glass microelectrodes and the effect of a number of intra-tubular and peritubular ionic substitutions tested. Impalement of single distal tubule cells indicated that the transepithelial potential difference is made up of 2 steps. The transepithelial potential difference is reduced when either the concentration of potassium is increased peri-tubularly, or the sum of the concentrations of sodium and potassium reduced within the lumen. This potential difference is elevated when intratubular chloride is replaced by sulfate, whereas the substitution of potassium by sodium leaves the potential difference unchanged. The data are consistent with the thesis that the peritubular cell membrane has a high and selective potassium permeability, whereas the luminal cell membrane is characterized by approximately equal permeabilities to sodium, potassium, and chloride. Given a cell compartment with a high-potassium and low-sodium concentration, these permeability properties, as well as the relative constancy of the sum of cations along the distal tubule, can probably account for the observed uniformity of the transtubular electrical potential difference along the distal tubule.