The potential and resistance profile of Necturus gallbladder cells

Summary

Necturus gallbladders were mounted in a modified Ussing chamber and the open circuit potential as well as the IR drop in response to transepithelial current were recorded while passing 2.7 molar KCl-filled microelectrodes in steps of 2–7 μm from the mucosal compartment across the cell into the subepithelial space and back. Using high-resistance electrodes the intracellular electrical potential was found to be independent of the depth of penetration of the electrode into the cell. It averaged −57.9 ±4.5 mV (n=39) with reference to the mucosal solution. Similarly, the resistance between microelectrode tip and mucosal solution was independent of the depth of insertion, indicating that the major part of the IR drop in response to transepithelial currents of 100 μA/cm² density occured at the cell membranes and that the IR drop inside the cytoplasm was negligibly small. The latter result agrees with quantitative estimates based on the cytoplasmic resistivity of other cells. Using low-resistance microelectrodes the existence of intracellular potential gradients could be simulated. The simultaneous resistance measurements, however, revealed that initial low potential readings must be interpreted as incomplete or leaky impalements. We conclude that active solute and water transport across Necturus gallbladder epithelium does not generate significant intracellular potential gradients.