Relationship between electrical and hydrogen ion gradients across rat proximal tubule

¹ Department of Medicine, New York University Medical Center, New York City

By means of micropuncture methods, proximal transtubular electrical potentials and tubular fluid pH were measured during isotonic sodium chloride or hypertonic dextrose infusion in normal rats and during sodium ferrocyanide infusion in salt-restricted rats. The mean electrical potential during sodium ferrocyanide infusion was significantly higher than in the other two groups (31.5 mv vs. 18 mv) and the mean tubular fluid pH was significantly lower (6.85 vs. 7.08). This parallel increase in electrical and concentration gradients with sodium ferrocyanide infusion suggests a passive component to hydrogen ion distribution across the tubular cells. Using the Nernst equation, equilibrium potentials were calculated from the observed hydrogen ion gradients. Almost all of these calculated potentials were found to be less than the observed electrical potentials and therefore the distribution of hydrogen ions in these experiments could be accounted for entirely by passive diffusion. It is postulated that poorly reabsorbable anions depolarize the luminal membrane to a greater extent than the peritubular membrane, thereby increasing both transtubular potential and hydrogen ion excretion.

Note:
(With the Technical Assistance of Hagop S. Aynedjian)