Bouzinova Elena V, Praetorius Jeppe, Virkki Leila V, Nielsen Søren, Boron Walter F, Aalkjaer Christian
Institute for Physiology and Biophysics, Univ. of Aarhus, Ole Worms Allé, Bldg. 1160, DK-8000 Aarhus C, Denmark.
Am J Physiol Cell Physiol. 2005 Dec;289(6):C1448-56. doi: 10.1152/ajpcell.00313.2005. Epub 2005 Aug 10.
Several studies suggest the involvement of Na+ and HCO3- transport in the formation of cerebrospinal fluid. Two Na+-dependent HCO3- transporters were recently localized to the epithelial cells of the rat choroid plexus (NBCn1 and NCBE), and the mRNA for a third protein was also detected (NBCe2) (Praetorius J, Nejsum LN, and Nielsen S. Am J Physiol Cell Physiol 286: C601-C610, 2004). Our goal was to immunolocalize the NBCe2 to the choroid plexus by immunohistochemistry and immunogold electronmicroscopy and to functionally characterize the bicarbonate transport in the isolated rat choroid plexus by measurements of intracellular pH (pHi) using a dual-excitation wavelength pH-sensitive dye (BCECF). Both antisera derived from COOH-terminal and NH2-terminal NBCe2 peptides localized NBCe2 to the brush-border membrane domain of choroid plexus epithelial cells. Steady-state pHi in choroidal cells increased from 7.03 +/- 0.02 to 7.38 +/- 0.02 (n=41) after addition of CO2/HCO3- into the bath solution. This increase was Na+ dependent and inhibited by the Cl- and HCO3- transport inhibitor DIDS (200 muM). This suggests the presence of Na+-dependent, partially DIDS-sensitive HCO3- uptake. The pHi recovery after acid loading revealed an initial Na+ and HCO3- -dependent net base flux of 0.828 +/- 0.116 mM/s (n = 8). The initial flux in the presence of CO2/HCO3- was unaffected by DIDS. Our data support the existence of both DIDS-sensitive and -insensitive Na+- and HCO3- -dependent base loader uptake into the rat choroid plexus epithelial cells. This is consistent with the localization of the three base transporters NBCn1, Na+-driven Cl- bicarbonate exchanger, and NBCe2 in this tissue.
多项研究表明，Na⁺和HCO₃⁻转运参与脑脊液的形成。最近，两种Na⁺依赖性HCO₃⁻转运体定位于大鼠脉络丛上皮细胞（NBCn1和NCBE），还检测到了第三种蛋白的mRNA（NBCe2）（普拉托里乌斯J、内尤姆LN和尼尔森S。《美国生理学杂志：细胞生理学》286：C601 - C610，2004）。我们的目标是通过免疫组织化学和免疫金电子显微镜将NBCe2定位到脉络丛，并通过使用双激发波长pH敏感染料（BCECF）测量细胞内pH（pHi）来功能表征分离的大鼠脉络丛中的碳酸氢盐转运。源自COOH末端和NH₂末端NBCe2肽的两种抗血清均将NBCe2定位于脉络丛上皮细胞的刷状缘膜结构域。向浴液中添加CO₂/HCO₃⁻后，脉络丛细胞中的稳态pHi从7.03±0.02升高至7.38±0.02（n = 41）。这种升高依赖于Na⁺，并被Cl⁻和HCO₃⁻转运抑制剂DIDS（200 μM）抑制。这表明存在Na⁺依赖性、部分对DIDS敏感的HCO₃⁻摄取。酸负荷后的pHi恢复显示，初始的Na⁺和HCO₃⁻依赖性净碱通量为0.828±0.116 mM/s（n = 8）。在有CO₂/HCO₃⁻存在时的初始通量不受DIDS影响。我们的数据支持在大鼠脉络丛上皮细胞中存在对DIDS敏感和不敏感的Na⁺和HCO₃⁻依赖性碱装载。这与该组织中三种碱转运体NBCn1、Na⁺驱动的Cl⁻-碳酸氢盐交换体和NBCe2的定位一致。
