ION-TRANSPORT ACROSS ISOLATED PIG JEJUNUM

Sodium, chloride, and glucose transport were studied in stripped pig jejunal epithelium mounted between halfchambers. The epithelium proved to be stable for experimental purposes for up to 2 h. Net sodium absorption was electrogenic and was dependent solely on sodium-glucose cotransport. Both sodium and glucose influx varied with mucosal glucose concentration; when fitted to the Michealis-Menten equation the two fluxes generated glucose-dependent Michaelis constant values of 1.5 and 9.6 mM, respectively. In the absence of mucosal glucose, the flux ratios for sodium and chloride were of unity, and the unidirectional fluxes were linearly dependent on the ion concentrations. The chloride accompanying sodium in open circuit was driven by the potential generated by the sodium-glucose absorption (-5 mV) and supported an absorption of 1-mu-mol.cm-2 .h-1 NaCl. Substituting 2-hydroxyethanesulfonate for chloride decreased total tissue conductance and reduced the sodium fluxes. This effect cannot be ascribed to sodium-chloride cotransport but reflects the different mobilities of the ion pairs in solution. Chloride secretion can be induced by theophylline.