title: Sugar-stimulated ion absorption is not different in seahare and vertebrate intestine.
abstract: We have reexamined the notion that sugars stimulate ion absorption differently in invertebrate and vertebrate intestine. In the seahare intestine, mucosal sugar presumably increases the rate of transcellular Na+ and Cl- absorption, whereas only transcellular Na+ absorption is increased in the vertebrate small intestine. Our data indicate that the seahare intestine responds to mucosal D-galactose like the vertebrate small intestine: namely, the apical membrane electrical potential difference depolarizes, the ratio of the mucosal to serosal membrane resistances decreases, and the short-circuit current (Isc) increases. Because mucosal substitution of tetramethylammonium for Na+ abolished the increased Isc, this stimulation resulted from an increase in rheogenic Na+ absorption. Unidirectional transepithelial Cl- fluxes indicate that mucosal D-galactose had no effect on the net Cl- flux under short-circuit conditions. Further, ion substitution experiments indicate that the apical membrane is K+ conductive rather than Cl- conductive as previously reported. These electrophysiological as well as parallel histological findings indicate that studies previously reported on the seahare intestine were in fact conducted on the esophagus.
mesh_terms: D000818:Animals; D001048:Aplysia; D004947:Esophagus / Q000187:drug effects / Q000502:physiology; D005690:Galactose / Q000494:pharmacology*; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects*; D007413:Intestinal Mucosa / Q000502:physiology; D007421:Intestine, Small / Q000502:physiology; D007422:Intestines / Q000187:drug effects / Q000502:physiology*; D008353:Mannitol / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D012016:Reference Values; D013045:Species Specificity
chemical_list: D008353:Mannitol; D005690:Galactose