Studies on the Electrical Potential Profile across Rabbit Ileum

When isolated strips of mucosal rabbit ileum are bathed by physiological electrolyte solution the electrical potential difference (PD) across the brush border (psi(mc)) averages 36 mv, cell interior negative. Rapid replacement of Na in the mucosal solution with less permeant cations, Tris or choline, results in an immediate hyperpolarization of psi(mc). Conversely, replacement of choline in the mucosal solution with Na results in an abrupt depolarization of psi(mc). These findings indicate that Na contributes to the conductance across the brush border. The presence of actively transported sugars or amino acids in the mucosal solution brings about a marked depolarization of psi(mc) and a smaller increase in the transmural PD (Deltapsi(ms)). It appears that the Na influx that is coupled to the influxes of amino acids and sugars is electrogenic and responsible for the depolarization of psi(mc). Under control conditions Deltapsi(ms) can be attributed to the depolarization of psi(mc) together with the presence of a low resistance transepithelial shunt, possibly the lateral intercellular spaces. However, quantitatively similar effects of amino acids on psi(mc) are also seen in tissues poisoned with metabolic inhibitors or ouabain. Under these conditions Deltapsi(mc) is much smaller than under control conditions. Thus, the depolarization of psi(mc) might not account for the entire Deltapsi(ms), observed in nonpoisoned tissue. An additional electromotive force which is directly coupled to metabolic processes might contribute to the normal Deltapsi(ms).