Transmembrane Electrical Potential Differences and Ionic Composition of Mucosal Cells of Rat Colon

Using glass microelectrodes, stable electrical potential differences (p.d.) have been measured across the cell membranes of mucosal cells of rat colon in vivo and in vitro in tissue mounted in a chamber. The intracellular content of Na, K, Cl and water has been determined under similar conditions. The serosal transmembrane p.d. was slightly greater than the luminal transmembrane p.d., in both cases the inside of the cell being negative with respect to the exterior. The cell Na content was low and cell K high when compared with extracellular fluid but the transmembrane p.d. measurements were considerably less than expected if they were simply K diffusion potentials. The present results have been considered in the relationship to the known ionic fluxes and it is suggested that a) Na and K ‘pumps’ are present on the serosal side of the mucosal cells and b) that, since the transmembrane fluxes of Na and Cl are inconsistent with the observed transmembrane potentials and the mucosal ionic composition, the bulk of these ions cross the mucosa either through special cells or by pathways between the cells.