Effect of Luminal Sodium Concentration on Bicarbonate Absorption in Rat Jejunum

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Abstract

An exchange of Na+ for H+ has been proposed to explain why jejunal Na+ absorption is influenced by luminal concentrations of H+ and HCO3-. We studied the influence of luminal Na+ concentration on net HCO3- absorption by perfusing rat jejunum in vivo. When Na+ was omitted from the perfusion fluid, HCO3- absorption diminished by a fixed amount over a range of initial HCO3- concentrations of 15 to 80 mM. This change was not caused by alterations in transmural PD or direction of water movement. Because the rate of HCO3- absorption decreased as the luminal HCO3- concentration lessened, Na+-dependent HCO3- absorption accounted for an increasing percent of total absorption as the luminal concentration of HCO3- diminished.

Authors

Kenneth A. Hubel