title: Characterization of Ca2+ transport in rat renal brush-border membranes and its modulation by phosphatidic acid.
abstract: The Ca2+ transport process by isolated renal brush-border membranes was characterized and the influence of the acidic phospholipid phosphatidic acid (PtdA) on this transport process was assessed. Ca2+ uptake by brush-border membranes exhibited saturation kinetics. It was inhibitable by a variety of multivalent cations, as well as by Ca2+-entry inhibitors, including verapamil, Ruthenium Red and gentamicin. It was selective for Ca2+ compared with Mg2+. This process was also electrophoretic since generation of K+ and anion-diffusion potentials, negative inside the vesicle, increased Ca2+ uptake. Elevations in PtdA content of brush-border membranes by either exogenous addition or endogenous generation of PtdA by incubating brush-border membranes with MgATP2- elevated the rate of Ca2+ uptake. This ATP effect could not be attributed to (Ca2+ + Mg2+)-dependent ATPase or contaminating membrane fragments. PtdA also increased the magnitude and rate of Ca2+ efflux from brush-border membranes preloaded with Ca2+. These modulations in uptake and efflux were not observed with phosphatidylcholine or phosphatidylinositol. In summary, these results are consistent with the presence of an electrophoretic uniport system for Ca2+ in renal brush-border membranes, and demonstrate that PtdA uniquely among phospholipids tested appears to facilitate transmembrane flux of Ca2+ across this membrane preparation.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D000838:Anions / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002412:Cations / Q000494:pharmacology; D066298:In Vitro Techniques; D007672:Kidney Cortex / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism; D010712:Phosphatidic Acids / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D051381:Rats
chemical_list: D000838:Anions; D002412:Cations; D010712:Phosphatidic Acids; D000255:Adenosine Triphosphate; D011188:Potassium; D002118:Calcium