Kohn O F, Mitchell P P, Steinmetz P R
Division of Nephrology, University of Connecticut School of Medicine, Farmington 06032.
Am J Physiol. 1990 Jan;258(1 Pt 2):F9-14. doi: 10.1152/ajprenal.1990.258.1.F9.
The apical anion exchanger of the beta-carbonic anhydrase (CA) cells differs from the basolateral exchanger of the alpha-cells by reduced sensitivity to disulfonic stilbenes and lack of immunoreactivity with antibodies to erythrocyte band 3 protein. To characterize the exchanger, we examined the effects on electroneutral bicarbonate secretion (JHCO3n) of Cl- replacement by gluconate, Br-, SO4(2-), and NO3- and of inhibition by 1) acetazolamide (ACZ) with and without pretreatment with sodium azide (NaN3), 2) furosemide, and 3) alpha-cyano-4-hydroxycinnamate (CHC). The Cl-dependent JHCO3n was 0.90 +/- 0.09 mumol/h, similar to the ACZ-inhibitable rate of 0.83 +/- 0.08 mumol/h with an apparent Km for Cl near 3.4 mM. Maximal JHCO3n was comparable at luminal pH 6.8 and 4.5. JHCO3n was reduced to approximately 21% in Br-, 13% in SO4(2-), and 7% in NO3- solutions compared with the rates in chloride solutions. ACZ inhibition was not abolished by pretreatment with NaN3. JHCO3n was only slightly inhibited (14%) by furosemide and not inhibited by CHC. In conclusion, the apical exchanger is selective for chloride and relatively resistant to inhibitors. Its dependence on luminal chloride is such that its transport rate is closely regulated by mucosal chloride at concentrations below 20 mM.
β - 碳酸酐酶（CA）细胞的顶端阴离子交换器与α细胞的基底外侧交换器不同，对二磺酸芪的敏感性降低，并且与抗红细胞带3蛋白抗体缺乏免疫反应性。为了表征该交换器，我们研究了用葡萄糖酸盐、Br -、SO4(2 -)和NO3 -替代Cl -以及用以下物质抑制对电中性碳酸氢盐分泌（JHCO3n）的影响：1）乙酰唑胺（ACZ），有无叠氮化钠（NaN3）预处理；2）呋塞米；3）α - 氰基 - 4 - 羟基肉桂酸酯（CHC）。Cl - 依赖性JHCO3n为0.90±0.09 μmol/h，类似于ACZ可抑制的速率0.83±0.08 μmol/h，Cl - 的表观Km接近3.4 mM。在管腔pH 6.8和4.5时，最大JHCO3n相当。与氯化物溶液中的速率相比，在Br -溶液中JHCO3n降低至约21%，在SO4(2 -)溶液中降低至13%，在NO3 -溶液中降低至7%。用NaN3预处理并没有消除ACZ的抑制作用。JHCO3n仅被呋塞米轻微抑制（14%），而不被CHC抑制。总之，顶端交换器对氯离子具有选择性，并且对抑制剂相对耐药。它对管腔氯离子的依赖性使得其转运速率在低于20 mM的浓度下受到黏膜氯离子的密切调节。
