Membrane potentials of epithelial cells in rat small intestine.

1. Stripped sacs of rat jejunum in which the outer muscle layers had been removed were found to maintain substantial transport and electrical activities.2. Mucosal and serosal membrane potentials of epithelial cells of normal and stripped everted sacs of rat jejunum were recorded in vitro together with the transmural potential difference.3. The cell interior was negative relative to both serosal and mucosal fluids, the transmural potential being the sum of the two membrane potentials.4. Changes in the transmural potentials in the presence of actively transferred hexoses and amino acids were entirely due to variations in the serosal potential, the mucosal potential being unchanged.5. Serosal and transmural potential increases on the addition of galactose were consistent with Michaelis-Menten kinetics, giving apparent K(m) values of 14.9 and 14.1 mM respectively.6. Phlorrhizin, ouabain, 2,4-dinitrophenol and sodium fluoroacetate inhibited serosal potential changes in the presence of galactose.7. Osmotic potentials resulting from transmural osmotic gradients originated from the serosal layers of the tissue.8. The results are consistent with the concept of a serosally located, electrogenic sodium pump which is stimulated by actively transferred hexoses and amino acids. The sodium-dependent entry mechanism at the mucosal membrane is non-electrogenic.