Separate entry pathways for phosphate and oxalate in rat brain microsomes

Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322 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 ac...

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Bibliographic Details
Published in:American Journal of Physiology: Cell Physiology 2000-06, Vol.278 (6), p.C1183-C1190
Main Authors: Meng, X.-J, Timmer, R. T, Gunn, R. B, Abercrombie, R. F
Format: Article
Language:English
Subjects:
4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid - pharmacology
Adenosine Triphosphate - metabolism
Animals
Arsenates - pharmacology
Brain - metabolism
Calcium - metabolism
Endoplasmic Reticulum - drug effects
Endoplasmic Reticulum - metabolism
Kinetics
Male
Microsomes - drug effects
Microsomes - metabolism
Models, Biological
Niflumic Acid - pharmacology
Oxalates - metabolism
Oxalates - pharmacology
Phosphates - metabolism
Phosphates - pharmacology
Rats
Rats, Sprague-Dawley
Stilbenes - pharmacology
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Summary:Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322 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 µM), 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS; 250 µM), and DIDS (3-5 µM); accumulation during the initial stage was unaffected. Higher concentrations of DIDS (100 µM), 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. 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid; 4,4'-dinitrostilbene-2,2'-disulfonic acid; niflumic acid; endoplasmic reticulum; adenosine 3',5'-cyclic monophosphate; active calcium transport; calcium homeostasis
ISSN:0363-6143
1522-1563
DOI:10.1152/ajpcell.2000.278.6.c1183