title: NAD+-induced inhibition of phosphate transport in canine renal brush-border membranes. Mediation through a process other than or in addition to NAD+ hydrolysis.
abstract: We previously demonstrated inhibition of Na+-dependent 32Pi transport in canine renal brush-border membranes in association with NAD+-induced ADP ribosylation of membrane protein(s) and postulated that NAD+ inhibits Pi transport across the brush-border membrane via ADP ribosylation. Recently it was shown that incubation of rat brush-border membrane with NAD+ resulted in release of Pi which was prevented by EDTA. It was proposed that NAD+-mediated inhibition of 32Pi transport might occur through this mechanism. To determine whether NAD+ inhibited 32Pi transport by a mechanism other than or in addition to release of Pi, we compared Na+-dependent 32Pi counterflow in brush-border membrane equilibrated with Pi or with Pi generated from NAD+. Release of Pi from NAD+ incubated with brush-border membrane was confirmed. The increased uptake of 32Pi which was demonstrated in brush-border membrane equilibrated with Pi was not measured when intravesicular Pi was generated from a concentration of NAD+ which effected ADP-ribosylation of brush border membranes (100 microM NAD+). In contrast, increased uptake of 32Pi was demonstrated when intravesicular Pi was generated from 1 microM NAD+ which did not effect ADP ribosylation. Mg2+-dependent ADP ribosylation of brush-border membrane incubated with NAD+ was demonstrated which persisted during the time interval of 32Pi uptake measurements. Our findings are compatible with the hypothesis that NAD+-induced ADP ribosylation of brush-border membrane protein(s) results in inhibition of Pi transport across the membrane in vivo. EDTA may act to prevent this inhibition in brush-border membrane by chelation of Mg2+ and decreased ADP ribosylation.
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism*; D004285:Dogs; D007668:Kidney / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D008565:Membrane Proteins / Q000302:isolation & purification / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism* / Q000648:ultrastructure; D008970:Molecular Weight; D009243:NAD / Q000378:metabolism / Q000494:pharmacology*; D010710:Phosphates / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism
chemical_list: D008565:Membrane Proteins; D010710:Phosphates; D009243:NAD; D000246:Adenosine Diphosphate Ribose; D012964:Sodium; D008274:Magnesium