Micropuncture study of proximal renal tubular chloride transport during hypercapnea in the rat

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Abstract
The electrical potential difference and the concentration of chloride in tubular fluid and plasma were measured in stopped-flow microperfusion of the proximal tubule of rats breathing either air or 12% CO2 in air. Perfusion with 10% PVP completely stopped net transtubular fluid movement. Chloride was not in electrochemical equilibrium under these conditions and hypercapnea increased the concentration of chloride in tubular fluid relative to that in plasma. This suggests that the net reabsorption of chloride must overcome a force which moves chloride into the tubular lumen. An anion pump is postulated which secretes chloride into the tubular lumen and is linked to acidification of proximal tubular fluid.