Reference

Citrate transport in proximal cell line

Citrate transport in proximal cell line. Law, D.; Hering-Smith, K. S.; Hamm, L. L. (Sch. Med., Washington Univ., St. Louis, MO 63110, USA). Am. J. Physiol., 263(1, Pt. 1), C220-C225 (English) 1992. CODEN: AJPHAP. ISSN: 0002-9513. DOCUMENT TYPE: Journal CA Section: 13 (Mammalian Biochemistry) Citrate uptake into kidney proximal tubules occurs via an apical dicarboxylate transporter and a poorly characterized process in the basolateral membrane. The authors used OK cells, a cell line derived from opossum kidney, to study citrate transport in proximal tubule-like cells. Citrate uptake into cell monolayers was studied using [14C]citrate with [3H]mannitol as a vol. marker. Citrate uptake into these cells was sodium dependent and saturable with increasing concns. of citrate. In contrast to previous models, citrate transport was altered minimally by changes in pH from 6.2 to 7.0 and increased at pH 7.4 to 7.8. A variety of di- and tricarboxylates were tested for interaction with citrate transport. The dicarboxylates succinate, malate, and oxaloacetate at 1 mM concn. inhibited citrate uptake minimally (uptake at least 80% of control); one dicarboxylate, a-ketoglutarate, did inhibit citrate uptake significantly. In contrast, the tricarboxylates isocitrate and tricarballylate inhibited citrate uptake significantly, indicating probable competitive inhibition with the transport process. These characteristics are distinctly different from those of the apical membrane dicarboxylate transporter. 1,2,3-Benzenetricarboxylic acid, an inhibitor of the mitochondrial tricarboxylate transporter, did not alter citrate uptake. In conclusion, the OK proximal cell line exhibits a novel citrate transport process compared with the apical transport of citrate described in most proximal systems. This transport process probably involves the trivalent species of citrate in contrast to the usual predominant transport of divalent citrate. This transport process may represent a process similar to that in the basolateral membrane of the proximal tubule.

Quantitative determination of the citric acid carrier in mitochondrial membranes

Quantitative determination of the citric acid carrier in mitochondrial membranes. Part I. Stipani, I.; Genchi, G.; Palmieri, F. (Ist. Chim. Biol., Univ. Bari, Bari, Italy). Boll. Soc. Ital. Biol. Sper., 52(16), 1282-7 (Italian) 1976. CODEN: BSIBAC. DOCUMENT TYPE: Journal CA Section: 6 (General Biochemistry) Section cross-reference(s): 3 1,2,3-Benzenetricarboxylic acid (I) is a specific inhibitor of the citrate carrier in rat liver mitochondria; it blocked citrate transport without affecting malonate or .alpha.-ketoglutarate transport. I blocked the citrate carrier without itself being transported into the mitochondria. The binding of I-3H to mitochondria increased with increasing time and temp. of incubation but could be reversed by addn. of excess citrate. The binding of I to the mitochondria reflects the amt. of citrate carrier present on the surface of the mitochondrial membrane.