title: Na+ gradient-dependent transport of hypoxanthine by calf intestinal brush border membrane vesicles.
abstract: The properties of hypoxanthine transport were investigated in purified brush border membrane vesicles isolated from calf proximal and distal jejunum. Hypoxanthine uptake in the vesicles was stimulated by a transmembrane Na(+) gradient and an inside negative potential resulting in a transient accumulation of intravesicular hypoxanthine, especially in the proximal jejunum. Na(+)-dependent hypoxanthine uptake at this site seemed to occur by two saturable transport systems, a high affinity (K(m)=0.33 micromol/l) and a low affinity (K(m)=165 micromol/l) transporter. Guanine, hypoxanthine, thymine and uracil inhibited intravesicular hypoxanthine uptake, whereas adenine and the nucleosides inosine and thymidine were without effect. These findings represent the first demonstration of active Na(+) gradient-dependent nucleobase transport in intestinal brush border membrane vesicles.
authors.affiliation: Institute of Veterinary Physiology, University of Zurich, Winterthurerstrasse 260, CH-8057 Zurich, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Theisinger
authors.forename: B
authors.initials: B
authors.lastname: Grenacher
authors.forename: E
authors.initials: E
authors.lastname: Scharrer
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D002417:Cattle; D019271:Hypoxanthine / Q000493:pharmacokinetics*; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000648:ultrastructure*; D017136:Ion Transport; D007583:Jejunum / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism; D033702:Nucleobase Transport Proteins / Q000502:physiology; D012964:Sodium / Q000378:metabolism*
chemical_list: D033702:Nucleobase Transport Proteins; D019271:Hypoxanthine; D012964:Sodium