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Figure 5 | Cerebrospinal Fluid Research

Figure 5

From: Multiplicity of cerebrospinal fluid functions: New challenges in health and disease

Figure 5

Ion transporters and channels in mammalian choroidal epithelium. Typical CPe is schematized to localize transporters and channels that transfer ions and water [290]. CSF secretion results from coordinated transport of ions and water from basolateral membrane to cytoplasm, then sequentially across apical membrane into ventricles. On the plasma-facing membrane is parallel Na+-H+ and Cl--HCO3- exchange [38] bringing Na+ and Cl- into cells in exchange for H+ and HCO3-, respectively. Also basolaterally located is Na+-HCO3- cotransport (NBCn1) [41] and Na-dependent Cl--HCO3- exchange [42] that modulate pH and perhaps CSF formation. Apical Na+ pumping [49, 110] maintains a low cell Na+ that sets up a favorable basolateral gradient to drive Na+ uptake. Na+ is extruded into CSF mainly via the Na+ pump [110] and, under some conditions, the Na+-K+-2Cl- cotransporter [46]. K+-Cl- cotransport helps maintain cell volume [50]. Apical channels facilitate K+, Cl- and HCO3- diffusion into CSF [68]. Aquaporin 1 channels on CSF-facing membrane [77] mediate water flux into ventricles. Polarized distribution of carbonic anhydrase (c.a.) and Na+-K+-ATPase [51], and aquaporins, enable net ion and water translocation to CSF.

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