THE SODIUM, POTASSIUM AND CHLORIDE OF CEREBRAL TISSUES: MAINTENANCE, CHANGE ON STIMULATION AND SUBSEQUENT RECOVERY

Abstract

Cerebral tissues were prepared for incubation by cutting them from the brain rapidly and in situ, and the Ca concentration in the incubating medium was altered from the customary 2. 8m[image] to 0. 75 m[image]. This provided incubated cerebral cortex with fluid and ion content more closely resembling that of the brain in vivo than hitherto obtained. From a systematic difference in size between inulin spaces of slices with 1 and those with 2 cut surfaces, it was estimated that cutting directly affected a layer 0. 02 mm. thick. On the basis of the volume of this layer, it was calculated that the portion of the tissue not affected by cutting had an inulin space of 258 [mu]1. /g. initial wt., and during the process of preparation and incubation had gained 30 [mu] equiv. of Na and 17 [mu] equiv. of Cl/g. and had lost 14 [mu] equiv. of K/g. Several aspects of the ion content of the incubated tissue were compatible with the observed membrane potential of -60mV between cellular and extracellular phases. In response to electrical stimulation, Na of the non-inulin space increased from 28 to 57 [mu] equiv. /g., K decreased from 68 to 48 [mu] equiv. /g. and Cl increased from 16 to 22 [mu] equiv. /g. in the non-inulin space. These changes were complete in about 6 min., and thereafter the concentrations remained steady during continued stimulation. Initial rates of change were 460 [mu] equiv. /g. /hr. for Na and 480 [mu] equiv. /g. /hr. for K. After stimulation was stopped the ionic composition of the tissue returned completely to its pre-stimulation state within 10 min. Initial rates for extrusion of Na and gain of K were 160 and 230 [mu] equiv. /g. /hr. respectively.