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Fig. 16 | Fluids and Barriers of the CNS

Fig. 16

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

Fig. 16

Simplified scheme for explaining the initial results of ion substitutions and inhibition by 4,4′-diisothiocyano-2,2′-stilbenedisulfonic acid (DIDS). In a the rates of acid loading by Cl/HCO3 exchange and acid extrusion by Na+, HCO3 -cotransport are nearly in balance and the pH is stable. In b removal of external Na+ reverses the direction of the Na+ gradient and Na+, HCO3 -cotransport is acid loading until the internal Na+ is depleted. While both types of transport are acid loading, pHi falls, i.e. there is cellular acidification. In c removal of external Cl reverses the direction of the Cl gradient and Cl/HCO3 exchange is acid extruding until the internal Cl is depleted. While both types of transport are acid extruding, pHi increases, i.e. there is cellular alkalinization. In d DIDS blocks both types of transport and there is little acid loading or extrusion and only slow if any change in pHi

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