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Am J Physiol. 1983 Dec;245(6):R853-9.

Control of extracellular ions in skate brain during osmotic disturbances.


Regulation of brain water and osmolytes in osmotic disturbances has been studied in the little skate, Raja erinacea. Free-swimming fish were subjected to seawater plus 125 mM NaCl (hyperosmotic; these also received 10 ml/kg body wt im 4.19 M NaCl in elasmobranch Ringer) or to 50% seawater (hyposmotic). At a set time, fish were killed, and blood and brain (telencephalon and medulla) were analyzed. Brain water was divided into a Cl- and a non-Cl- space. Responses of water and osmolytes to osmotic disturbances were mutually consistent. In telencephalon, there was good regulation of Cl- space, based on Na+ and Cl- shifts in hypo- and hyperosmolality. This control was near perfect at 2- and 4-h hyperosmolality. Regulation of non-Cl- space was minimal at 24-h hyperosmolality, with small K+ uptake. In medulla, Cl- space and ions were unregulated, whereas non-Cl- space was partly controlled in hyposmolality in relation to amino acid loss. Thus in this elasmobranch, regulation of Cl- space and of Na+ and Cl- is effective in telencephalon but is nonexistent in medulla oblongata.

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