Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.
Am J Physiol Cell Physiol. 2010 Jun;298(6):C1363-75. doi: 10.1152/ajpcell.00004.2010. Epub 2010 Mar 10.
Nephrolithiasis in the Slc26a6(-/-) mouse is accompanied by 50-75% reduction in intestinal oxalate secretion with unchanged intestinal oxalate absorption. The molecular identities of enterocyte pathways for oxalate absorption and for Slc26a6-independent oxalate secretion remain undefined. The reported intestinal expression of SO(4)(2-) transporter SLC26A2 prompted us to characterize transport of oxalate and other anions by human SLC26A2 and mouse Slc26a2 expressed in Xenopus oocytes. We found that hSLC26A2-mediated [(14)C]oxalate uptake (K(1/2) of 0.65 +/- 0.08 mM) was cis-inhibited by external SO(4)(2-) (K(1/2) of 3.1 mM). hSLC26A2-mediated bidirectional oxalate/SO(4)(2-) exchange exhibited extracellular SO(4)(2-) K(1/2) of 1.58 +/- 0.44 mM for exchange with intracellular [(14)C]oxalate, and extracellular oxalate K(1/2) of 0.14 +/- 0.11 mM for exchange with intracellular (35)SO(4)(2-). Influx rates and K(1/2) values for mSlc26a2 were similar. hSLC26A2-mediated oxalate/Cl(-) exchange and bidirectional SO(4)(2-)/Cl(-) exchange were not detectably electrogenic. Both SLC26A2 orthologs exhibited nonsaturable extracellular Cl(-) dependence for efflux of intracellular [(14)C]oxalate, (35)SO(4)(2-), or (36)Cl(-). Rate constants for (36)Cl(-) efflux into extracellular Cl(-), SO(4)(2-), and oxalate were uniformly 10-fold lower than for oppositely directed exchange. Acidic extracellular pH (pH(o)) inhibited all modes of hSLC26A2-mediated anion exchange. In contrast, acidic intracellular pH (pH(i)) selectively activated exchange of extracellular Cl(-) for intracellular (35)SO(4)(2-) but not for intracellular (36)Cl(-) or [(14)C]oxalate. Protein kinase C inhibited hSLC26A2 by reducing its surface abundance. Diastrophic dysplasia mutants R279W and A386V of hSLC26A2 exhibited similar reductions in uptake of both (35)SO(4)(2-) and [(14)C]oxalate. A386V surface abundance was reduced, but R279W surface abundance was at wild-type levels.
Slc26a6(-/-) 小鼠的肾结石形成伴随着肠道草酸盐分泌减少 50-75%，而肠道草酸盐吸收不变。用于草酸盐吸收和 Slc26a6 非依赖性草酸盐分泌的肠细胞途径的分子身份仍未确定。报告的肠道 SO(4)(2-)转运体 SLC26A2 的表达促使我们表征人 SLC26A2 和在非洲爪蟾卵母细胞中表达的小鼠 Slc26a2 对草酸盐和其他阴离子的转运。我们发现 hSLC26A2 介导的 [(14)C]草酸盐摄取（K(1/2)为 0.65 +/- 0.08 mM）被外部 SO(4)(2-)顺式抑制（K(1/2)为 3.1 mM）。hSLC26A2 介导的草酸盐/SO(4)(2-)双向交换表现出细胞外 SO(4)(2-)的 K(1/2)为 1.58 +/- 0.44 mM，用于与细胞内 [(14)C]草酸盐交换，以及细胞外草酸盐的 K(1/2)为 0.14 +/- 0.11 mM，用于与细胞内 (35)SO(4)(2-)交换。mSlc26a2 的流入率和 K(1/2)值相似。hSLC26A2 介导的草酸盐/Cl(-)交换和双向 SO(4)(2-)/Cl(-)交换均不是电活性的。两个 SLC26A2 同源物均表现出对细胞内 [(14)C]草酸盐、(35)SO(4)(2-)或 (36)Cl(-)流出的非饱和细胞外 Cl(-)依赖性。进入细胞外 Cl(-)、SO(4)(2-)和草酸盐的 (36)Cl(-)流出的速率常数均比相反方向的交换低 10 倍。酸性细胞外 pH(pH(o))抑制了 hSLC26A2 介导的所有阴离子交换方式。相比之下，酸性细胞内 pH(pH(i))选择性地激活了细胞外 Cl(-)与细胞内 (35)SO(4)(2-)而不是细胞内 (36)Cl(-)或 [(14)C]草酸盐的交换。蛋白激酶 C 通过减少其表面丰度来抑制 hSLC26A2。成骨不全症突变体 R279W 和 A386V 的 hSLC26A2 摄取 (35)SO(4)(2-)和 [(14)C]草酸盐的能力均相似降低。A386V 的表面丰度降低，但 R279W 的表面丰度处于野生型水平。
