Jennings M L, Adame M F
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77555, USA.
J Gen Physiol. 1996 Jan;107(1):145-59. doi: 10.1085/jgp.107.1.145.
This paper describes characteristics of the transport of oxalate across the human erythrocyte membrane. Treatment of cells with low concentrations of H2DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonate) inhibits Cl(-)-Cl- and oxalate-oxalate exchange to the same extent, suggesting that band 3 is the major transport pathway for oxalate. The kinetics of oxalate and Cl- self-exchange fluxes indicate that the two ions compete for a common transport site; the apparent Cl- affinity is two to three times higher than that of oxalate. The net exchange of oxalate for Cl-, in either direction, is accompanied by a flux of H+ with oxalate, as is also true of net Cl(-)-SO4(2-) exchange. The transport of oxalate, however, is much faster than that of SO4(2-) or other divalent anions. Oxalate influx into Cl(-)-containing cells has an extracellular pH optimum of approximately 5.5 at 0 degrees C. At extracellular pH below 5.5 (neutral intracellular pH), net Cl(-)-oxalate exchange is nearly as fast as Cl(-)-Cl- exchange. The rapid Cl(-)-oxalate exchange at acid extracellular pH is not likely to be a consequence of Cl- exchange for monovalent oxalate (HOOC-COO-; pKa = 4.2) because monocarboxylates of similar structure exchange for Cl- much more slowly than does oxalate. The activation energy of Cl(-)-oxalate exchange is about 35 kCal/mol at temperatures between 0 and 15 degrees C; the rapid oxalate influx is therefore not a consequence of a low activation energy. The protein phosphatase inhibitor okadaic acid has no detectable effect on oxalate self-exchange, in contrast to a recent finding in another laboratory (Baggio, B., L. Bordin, G. Clari, G. Gambaro, and V. Moret. 1993. Biochim. Biophys. Acta. 1148:157-160.); our data provide no evidence for physiological regulation of anion exchange in red cells.
本文描述了草酸盐跨人红细胞膜转运的特征。用低浓度的H2DIDS（4,4'-二异硫氰基芪-2,2'-二磺酸盐）处理细胞，对Cl(-)-Cl-和草酸盐-草酸盐交换的抑制程度相同，这表明带3蛋白是草酸盐的主要转运途径。草酸盐和Cl-自交换通量的动力学表明，这两种离子竞争一个共同的转运位点；Cl-的表观亲和力比草酸盐高两到三倍。草酸盐与Cl-的净交换，无论方向如何，都伴随着H+与草酸盐的通量，净Cl(-)-SO4(2-)交换也是如此。然而，草酸盐的转运比SO4(2-)或其他二价阴离子快得多。在0℃时，草酸盐流入含Cl(-)的细胞，细胞外pH的最适值约为5.5。在细胞外pH低于5.5（细胞内pH为中性）时，净Cl(-)-草酸盐交换几乎与Cl(-)-Cl-交换一样快。在酸性细胞外pH下快速的Cl(-)-草酸盐交换不太可能是Cl-与一价草酸盐（HOOC-COO-；pKa = 4.2）交换的结果，因为结构相似的单羧酸盐与Cl-的交换比草酸盐慢得多。在0至15℃之间的温度下，Cl(-)-草酸盐交换的活化能约为35千卡/摩尔；因此，草酸盐的快速流入不是低活化能的结果。与另一个实验室最近的发现（Baggio, B., L. Bordin, G. Clari, G. Gambaro, and V. Moret. 1993. Biochim. Biophys. Acta. 1148:157-160.）相反，蛋白磷酸酶抑制剂冈田酸对草酸盐自交换没有可检测到的影响；我们的数据没有提供红细胞中阴离子交换生理调节的证据。
