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Fig. 6 | Fluids and Barriers of the CNS

Fig. 6

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

Fig. 6

Ion transporters and transport pathways involved in normal secretion by the choroid plexus based on the description in Damkier et al. [4] with some modifications. See also [542]. On the CSF side, Na+, K+-ATPase actively transports Na+ out of and K+ into the epithelial cell, maintaining the gradients that drive the other ion movements indicated. The red circle used in the symbol for this pump 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 . On the blood side, dashed arrows in the symbol for the Na+, HCO3 -cotransporter, NCBE/NBCn2, indicate the involvement of H+ and Cl if the transporter is NCBE, but not if the transporter is NBCn2. On the CSF side, transport via the Na+, K+, 2 Cl-cotransporter, NKCC1, could be in either direction depending on the concentrations of Na+, K+, and Cl on the two sides of the membrane: for the concentrations in Table 1 transport is outward as shown. The electrical potential inside the cells is substantially negative while the CSF is somewhat positive relative to the fluid on the blood side of the epithelium. The source of the current that maintains the potential in the CSF may be the blood–brain barrier (see Sects. 3.7, 6.4 with its associated footnotes)

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