Separate entry pathways for phosphate and oxalate in rat brain microsomes

• 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
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.2000.278.6.c1183

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