Abstract
Simultaneous measurements of net ion and water fluxes were made in the stripped intestine of the seawater eel, and the relationship between Na+, K+, Cl− and water transport were examined in the presence of mucosal KCl and serosal NaCl Ringer (standard condition). When Cl− was removed from both sides of the intestine, net K+ flux from mucosa to serosa was reduced, accompanied by complete blockage of water absorption. Since it has been shown that net Cl− and water fluxes depend on K+ transport under the standard condition (Ando 1983), the interdependence of K+ and Cl− transport suggests the existence of a coupled KCl transport system, while the parallelism between the net Cl− and water fluxes suggests that water absorption is linked to the coupled KCl transport. The coupled KCl and water transport were inhibited by treatment with ouabain or with Na+-free Ringer solutions, suggesting the existence of a Na+-dependent KCl transport system and linkage of water absorption to the coupled Na+−K+−Cl− transport. Since ouabain blocked the active Na+−K+−Cl− transport almost completely, the permeability coefficients for K+ and Na+ through the paracellular shunt pathway were estimated as PK=0.076 and PNa=0.058 cm/h, and PCl was calculated as 0.005 cm/h. Although Na+-independent K+ and Cltt- fluxes were observed again in the present study, these fluxes were not inhibited by CN−, ouabain or diuretics, and evoked even after blocking the Na+−K+−Cl− transport completely with ouabain. These results indicate that the Na+-independent K+ and Cl− fluxes are distinct from the active Na+−K+−Cl− transport and are not themselves active.
Published Version
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