Electrolyte transport in rabbit ileum

Na and Cl transport across rabbit ileum in vitro was studied using a variety of bathing solutions. In solutions containing Cl and/or HCO₃, short circuit current (I(sc)) was always greater than net Na flux, but in Cl HCO₃ free solution (Cl and HCO₃ replaced by isethionate) net Na flux was greater than I(sc). Addition of HCO₃ to the bathing solutions in the presence or absence of Cl caused a decrease in net Na absorption with little change in I(sc), and addition of HCO₃ in the presence of Cl caused a decrease in net Cl secretion. Addition of Cl in the presence or absence of HCO₃ caused an increase in I(sc) but little change in net Na flux. There was no net flux of Cl in Na free solution. These observations are consistent with the presence of two ion transport systems in the ileum, one mediating Na absorption and one mediating electrolyte secretion. The secretory system could involve either electrogenic anion transport or neutral transport of NaCl and/or NaHCO₃, but detailed examination of the results suggests that the latter may be somewhat more likely.