title: Electrodiffusive transport of Mg across renal membrane vesicles of the rainbow trout Oncorhynchus mykiss.
abstract: The mechanism of tubular Mg transport was investigated in membrane vesicles (MV) of trout kidneys prepared by differential centrifugation with sucrose. MV consisted largely of brush-border membranes, as indicated by high enrichments of brush-border membrane enzymes. Although measured transport of 28 Mg included a binding component, most membrane transport was into or out of an osmotically active space. There was no evidence for amiloride-sensitive Na/Mg exchange, nor was Mg uptake affected by the carboxyl group reagents trimethyloxonium tetrafluoroborate, glycine methyl ester.HCl-1-ethyl-3- (3-dimethyl-aminopropyl)carbodiimide, and N,N'-dicyclohexyl carbodiimide or the Ca channel modulators D-600, verapamil, diltiazem, and BAY K 8644. However, Mg uptake increased in the presence of inside-negative voltages generated by inward gradients of the permeant anions NO3, SCN, and Cl or by outward gradients of K (plus valinomycin). Alkaline-earth cations displayed the selectivity sequence VII (Mg > Ca > Sr > Ba) for cis-inhibition of 28 Mg uptake. Mg efflux was trans-inhibited by La and Gd, and Mg uptake was cis-inhibited by Mn. The sulfhydryl group reagents p- chloromercuribenzoic acid and p-chloromercuriphenylsulfonate stimulated Mg uptake and efflux. These results reveal an electrodiffusive pathway for Mg transport in trout renal MV.
authors.affiliation: Department of Epithelial Physiology, Max-Planck-Institute for Molecular Physiology, Dortmund, Germany.
authors.forename: C A
authors.initials: CA
authors.lastname: Freire
authors.forename: R K
authors.initials: RK
authors.lastname: Kinne
authors.forename: E
authors.initials: E
authors.lastname: Kinne-Saffran
authors.forename: K W
authors.initials: KW
authors.lastname: Beyenbach
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002412:Cations / Q000494:pharmacology; D004058:Diffusion; D004558:Electric Stimulation; D005260:Female; D007474:Ion Exchange; D007668:Kidney / Q000378:metabolism*; D008274:Magnesium / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000493:pharmacokinetics*; D008297:Male; D008871:Microvilli / Q000378:metabolism; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D002412:Cations; D013438:Sulfhydryl Compounds; D000584:Amiloride; D012964:Sodium; D008274:Magnesium