title: Separate entry pathways for phosphate and oxalate in rat brain microsomes.
abstract: ATP-dependent (45)Ca uptake in rat brain microsomes was measured in intracellular-like media containing different concentrations of PO(4) and oxalate. In the absence of divalent anions, there was a transient (45)Ca accumulation, lasting only a few minutes. Addition of PO(4) did not change the initial accumulation but added a second stage that increased with PO(4) concentration. Accumulation during the second stage was inhibited by the following anion transport inhibitors: niflumic acid (50 microM), 4,4'-dinitrostilbene-2, 2'-disulfonic acid (DNDS; 250 microM), and DIDS (3-5 microM); accumulation during the initial stage was unaffected. Higher concentrations of DIDS (100 microM), however, inhibited the initial stage as well. Uptake was unaffected by 20 mM Na, an activator, or 1 mM arsenate, an inhibitor of Na-PO(4) cotransport. An oxalate-supported (45)Ca uptake was larger, less sensitive to DIDS, and enhanced by the catalytic subunit of protein kinase A (40 U/ml). Combinations of PO(4) and oxalate had activating and inhibitory effects that could be explained by PO(4) inhibition of an oxalate-dependent pathway, but not vice versa. These results support the existence of separate transport pathways for oxalate and PO(4) in brain endoplasmic reticulum.
authors.affiliation: Department of Physiology, Emory University School of Medicine, Atlanta, GA 30322, USA.
authors.forename: X J
authors.initials: XJ
authors.lastname: Meng
authors.forename: R T
authors.initials: RT
authors.lastname: Timmer
authors.forename: R B
authors.initials: RB
authors.lastname: Gunn
authors.forename: R F
authors.initials: RF
authors.lastname: Abercrombie
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001149:Arsenates / Q000494:pharmacology; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism*; D008954:Models, Biological; D009544:Niflumic Acid / Q000494:pharmacology; D010070:Oxalates / Q000378:metabolism* / Q000494:pharmacology; D010710:Phosphates / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013267:Stilbenes / Q000494:pharmacology
chemical_list: D001149:Arsenates; D010070:Oxalates; D010710:Phosphates; D013267:Stilbenes; D009544:Niflumic Acid; C022306:4,4'-dinitro-2,2'-stilbenedisulfonic acid; D000255:Adenosine Triphosphate; C025657:arsenic acid; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium