Extracellular fluid, ionic distribution and exchange in isolated frog brain

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Abstract
Brains of Rana pipiens were maintained in vitro for up to 3 hr. Normal frog brain contained H2O 83.1%, Cl 31, Na 43, and K 78 mEq/kg wet weight. No gain of H2O or loss of Koccurred on incubation. Na and Cl slightly diminished. The volumes of distribution of inulin-14C, sucrose - 14C, andsulphate-35s were 18.6, 23.7, and 21.5% respectively These indicators were largely equilibrated at. 30 min. Inulin and sucrose spaces increased slowly thereafter. The sulphate space was contant and prob-. ably most nearly represents the extracellular space. 24Na and 36Cl center the brain rapidly and the nonexchangeable fraction of these ions was less than 5%. The Na, Cl, and sulphate-35s spaces of rabbit cerebral cortex in vivo were similar to those of frog brain, which suggests that the former also has a large extracellular space of about 20%. The efflux of 24Na and 36Cl from preloaded frog brain into inactive fluid was complex, consisting of 3 exponential components. The spaces of fast moving 24Na and 36Cl were identical at 23.6%.