THE EFFECTS OF SODIUM, POTASSIUM AND CALCIUM ON METABOLISM OF RAT’S CEREBRAL CORTICAL SLICE WITH OR WITHOUT ELECTRICAL STIMULATION

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Abstract
By employing a modified procedure of slicing, it was possible to prepare several groups of tissue slices with almost identical respiratory and metabolic rates under environment from the same cerebral cortex. It was studied in respect to the O2 consumption, inorganic phosphate formation, and lactic acid production induced in the groups of slices stimultaneously incubated in normal environment or in modified environment in the presence or absence of electrical stimulation, and discussed on the role that external Na plays in metabolism of cerebral cortical slices. Twenty to 30% of the O2 uptake and metabolism induced in cerebral cortical slice under normal environment in the absence of electrical stimulation were effected by about 50-40 m[image] -external Na, and Na concentration above this was of no effect. Such metabolic effects of external Na are involved in the excitability of the tissues. The respiratory and metabolic responses of the tissue of electrical stimulation increased, far beyond the normal levels in the absence of electrical stimulation, with increase of the external Na concentration approximately in Michaelis-Menten fashion, and attained almost the maximum in the normal concentration of external Na. When external Na did not exist, the tissues did not respond to stimulation. Where the increases above the normal levels in metabolism and respiration of tissue without electrical stimulation are induced (even when the induced metabolism is indiscernibly small), most of the response to electrical stimulation was depressed. Such metabolic effects of external Na most probably originated in the Na adsorption in the membrane or its adjacent structure. The role of Na would probably be also in the metabolism associated with the excitatory process of the cell. External K,whatever its concentration, did not induce any respiratory or metabolic change in the tissue without external Na. Whether the external K was more or less than the normal concentration (about 7 m[image]), when the difference from the normal concentration was beyond a certain extent, the respiration and metabolism induced in the tissue without electrical stimulation with external Na always increased, but the response to electrical stimulation then were inversely depressed. K seems to affect mainly the excitability of the cell probably through the membrane potential and internal K content, and thereby control the absorption of external Na. By omitting Ca from the environment without Na, the respiration and metabolism of the tissue increased remarkably, but electrical stimulation was of no effect. The omission of Ca from normal medium caused a further increase in the respiration and lactic acid production of tissue more than in normal medium; the effect of electrical stimulation then hardly changed or seemed to be slightly depressed; therefore, these metabolic increases resulted from the increments induced in the tissue in medium without either Na or Ca; when the external Na existed, the increase of inorganic phosphate alone became always unusually small, whether or not electrical stimulation was applied. The respiration and metabolism of the tissue in the presence or absence of the external Na respectively were almost unaffected by the addition of external Ca, and the responses to stimulation appeared to be depressed slightly only in the presence of external Na. Essentially, Ca may only be concerned in the configuration of the membrane.
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