The sodium and other ions of mammalian cerebral tissues, maintained and electrically stimulated in vitro

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Abstract
Cerebral tissues incubated in oxygenated glucose-bicarbonate media rapidly gained Na about 40 uequiv of Na/g. by exchange with K and a similar quantity by uptake of NaCl, mainly during the first minute''s contact with the media. Attempts were made to minimize these changes by alterations in the incubating medium. A number of added substances were without such effect; preincubation in media low in sodium did not lead to lower tissue Na when, subsequently, slices were placed in media of normal Na content. Rapid preparation of tissue by cutting it in situ yielded samples of lower Na after incubation; during incubation, a net extrusion of Na was observed in such samples, at rates of 180-240 uequiv/g of tissue/hr. Electrical stimulation increased the Na content of the incubated tissue; after cessation of stimulation, the additional Na was in part extruded, again at about 200utequiv/g of tissue/ hr. Tissue incubated in media low in Na content, between 0 and 75 [image], was low in K content; when stimulated electrically, the respiratory rate of such tissues changed by -50 to +60% rather than by the +100% shown in media of normal Na content. The intracellular to extracellular ratios of Na+ and K+ ions (based on Cl and inulin spaces) have been calculated for incubated tissues prepared by different techniques and compared with the ratios (based on Cl space) in unincu-bated fresh tissue.