title: Transport of d-galactose by the gastrointestinal tract of the locust, Locusta migratoria.
abstract: Due to exoskeleton, the absorption of nutrients in adult insects takes place across the gastrointestinal tract epithelium. In most physiological studies, sugar intestinal absorption has been described as a diffusional process and to date no sugar transporter has been cloned from the digestive tract of insects. In the present work, the existence of a saturable transport system for galactose in the gastric caeca of Locusta migratoria is clearly demonstrated. This transport shows a relatively high affinity for galactose (apparent K0.5=2-3 mM) and is inhibited by glucose, 2-deoxyglucose and with less potency by fructose and alpha-methyl-d-glucoside. The absence of sodium or the presence of phloridzin hardly affects galactose absorption, indicating that it is not mediated by a SGLT1-like transporter. The absence of K+, Cl-, Mg2+ and Ca2+ or changes in the pH do not modify galactose absorption either. Nevertheless, phloretin, cytochalasin B and theophylline (inhibitors of facilitative transporters) decrease sugar uptake around 50%. Xenopus laevis oocytes microinjected with poly A+ RNA isolated from gastric caeca show sodium-independent galactose uptake that is three times higher than in non-injected oocytes, further supporting the existence of a mRNA coding for at least one equilibrative sugar transporter in L. migratoria gastric caeca.
authors.affiliation: Departamento de Fisiología y Nutrición, University of Navarra, C/ Irunlarrea s.n., 31008 Pamplona, Spain.
authors.forename: I
authors.initials: I
authors.lastname: Pascual
authors.forename: A
authors.initials: A
authors.lastname: Berjón
authors.forename: M P
authors.initials: MP
authors.lastname: Lostao
authors.forename: A
authors.initials: A
authors.lastname: Barber
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D003847:Deoxyglucose / Q000494:pharmacology; D005260:Female; D005690:Galactose / Q000378:metabolism*; D041981:Gastrointestinal Tract / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D048188:Locusta migratoria / Q000378:metabolism*; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D009004:Monosaccharide Transport Proteins; D003847:Deoxyglucose; D005947:Glucose; D005690:Galactose