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Fig. 17 | Fluids and Barriers of the CNS

Fig. 17

From: Fluid and ion transfer across the blood–brain and blood–cerebrospinal fluid barriers; a comparative account of mechanisms and roles

Fig. 17

One possible scheme for ion transport by the blood–brain barrier. The Na+-pump is shown with more on the abluminal than luminal side of the endothelial cells. Transporters shown with solid circles have been identified in the membrane indicated; those with dashed circles have been identified at a molecular level but not localized; while those with dotted circles or rectangles have been identified only functionally. The red circle used in the symbol for the Na+, K+-ATPase indicates that energy for the transport is input from hydrolysis of ATP. Arrows within the cell indicate transfers: in black Na+, in green K+, in red Cl, and in blue HCO3 . The electrical potential and ion concentrations inside the cells in vivo are not known. In primary cell culture the potential is about −40 mV [see e.g. 332]. Note that, in contrast to the choroid plexuses, at the blood–brain barrier there are likely to be conductances in both the luminal and abluminal membranes. NHE(1,2) is shown separately from the rest as it is unlikely to be active when pHi is in the normal range. However, it is strongly activated by low pHi as may occur in hypoxia/ischemia

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