Quantitation of Conductance Pathways in Antral Gastric Mucosa

The magnitude of cellular and shunt conductance of Necturus gastric antral mucosa was studied by (a) comparing the cellular PD response to transepithelial PD response during changes of ionic activity in the serosal bathing solution and (b) by measurement of current spread within the epithelial sheet. Using constant product KCI changes cellular resistance was 6,788 ~cm 2 and shunt resistance was 1,803 f/cm ~. Deletion of HCOifrom the serosal solution produced similar but quantitatively smaller changes in PD. Using HCOsdeletion cellular resistance was 7,338 f~cm 2 and shunt resistance was 1,973 12cm 2. Measurement of current spread within the mucosa avoids changing ionic gradients yet gave very similar results; cellular resistance was 8,967 [2cm 2 and shunt resistance was 2,947 ~2cm 2. The shunt contribution to transepithelial conductance ranged from 75.2 to 79.0%. Shunt selectivity was assessed using KCI dilution potentials, where mucosal dilution gave a small change in tissue PD compatible with an anion/cation selectivity ratio of 1.16 across the shunt, whereas serosal dilution effect was dominated by a PD change across the serosal membrane of the cell. The magnitude of the cellular and transepithelial shunt conductance of a variety of epithelia has been quantitated. The proximal tubule (Windhager et al., 1966; Hoshi and Sakai, 1967), gall bladder (Diamond et al., 1971; Fr6mter, 1972), and intestine (Clarkson, 1967; Frizzell and Schultz, 1972) can be classified as " leaky" tissues with the cell:shunt conductance ratio being 1 : 10-20. These epithelia demonstrate low transepithelial potential difference (PD), symmetry of PD response to changes in ionic activity, low transepithelial resistance, and failure to support large concentration gradients. In contrast, frog skin, toad bladder, and fundic gastric mucosa develop large concentration gradients, have a high PD, high transepithelial resistance, and have an asymmetric response to changes in ionic activity. These epithelia have cell to shunt conductance ratios > 1 (Mandel and Curran, 1972; Reuss and Finn, 1974; Spenney et al., 1974). T H E JOURNAL OF GENERAL PHYSIOLOGY " VOLUME 65, 1 9 7 5 • pages 645-662 645 on Jne 5, 2017 D ow nladed fom Published May 1, 1975