Effects of luminal hyperosmolality on cellular and paracellular ion transport pathways in Necturus antrum

Abstract

Using microelectrode techniques, the electrical properties of the cell membranes and paracellular pathway of the surface epithelium in Necturus antrum were studied under control conditions and during exposure to mucosal solutions made hyperosmotic by addition of sucrose or urea. Sucrose (500 mmol/kg) significantly decreased apical membrane resistances (Ra, from 5501 ± 841 to 3789 ± 597 Ω · cm2, p < 0.01), and basolateral membrane resistances (Rb, from 3805 ± 646 to 2594 ± 429 Ω · cm2, p < 0.05). The paracellular pathway resistance (Rs) increased significantly from 720 ± 57 to 822 ± 71 Ω · cm2 (p < 0.001). Urea (500 mmol/kg) more markedly diminished the apical and basolateral resistances (Ra, from 4303 ± 663 to 1914 ± 286 Ω · cm2, p < 0.001; and Rb, from 2600 ± 474 to 1034 ± 213, p < 0.001). In contrast to sucrose, urea-containing solutions significantly decreased Rs (from 682 ± 78 to 398 ± 57 Ω · cm2, p < 0.001). Electron micrographs revealed dilatation of lateral intercellular spaces and disruption of desmosomes in tissues exposed to urea, but no visible alterations in tissues exposed to solutions containing sucrose. The resistance of the cellular pathway to ion permeation was thus diminished during exposure to both solutes. In contrast, changes in resistance of the paracellular pathway appeared to depend on the effects of each solute on dimensions and structures of the intercellular pathways.