Electrical potential profile in rabbit ileum: role of rheogenic Na transport

The electrical potential profile of rabbit ileum was investigated in vitro with the microelectrode technique. The transmural electrical potential difference (PD), designated psims, was immediately reduced by 60% upon cooling the tissue from 37 to 7 degrees C; the PD across the mucosal membrane (transmucosal PD, psimc) was simultaneously reduced by 37%. These electrical changes could not be attributed to alternations in either transmembrane ion concentration gradients or total tissue conductance. The psimc and psims may have substantial values even after the concentration gradients of Na and K across the cell membane are eliminated, provided that active transport mechanisms are still operative. Conversely, in the presence of approximately normal transmembrane ion concentration gradients, but when active transport mechanisms have been inhibited. psimc is reduced by 45% and psims is zero. These observations are consistent with a model of electrolyte transport in which psims and the normal transmembrane cation concentration gradients are established by rheogenic active transport of Na out of the cell. The psimc is generated both by rheogenic active Na transport and by cation concentration gradients which exist across the cell membrane. The Koefoed-Johnsen and Ussing model (Acta Physiol. Scand., 1958, vol. 42, p. 298) of electrolyte transport by epithelial cells does not adequately describe the electrical properties of ileum.