Effects of inorganic salts and of ouabain on some metabolic responses of rat cerebral cortex slices to cationic and electrical stimulations

Abstract

The rate of glycine uptake, against a concentration gradient, into rat brain cortex slices, incubated in a physiological glucose medium, is proportional to the Na concentration of the medium and is independent of whether choline chloride or sucrose is used to balance diminished levels of Na. Choline, in contrast to sucrose, resembles Na in the maintenance of stimulated brain respiration but cannot replace Na for the stimulation of brain respiration by electrical impulses or by increased K concentrations. Electrical stimulation of rat brain slices, whilst resembling K stimulation in causing a fall in the level of ATP, differs from K stimulation in causing no diminution in the rate of glycine transport. This is due to the operation of 2 opposing processes: increased glycine influx due to increased influx of Na, and diminished glycine influx due to a decreased ATP level. The stimulation of rat brain respiration brought about by the application of electrical impulses or by the presence of high K concentrations, and the uptake of glycine against a concentration gradient, are controlled by the activity of membrane-bound ATPase. This conclusion is supported by: The presence of K is needed to obtain the optimal respiratory responses and the optimal rate of glycine uptake; ouabain inhibits the influx of glycine whether the brain tissue is in the stimulated condition or not and it also inhibits stimulated brain respiration; absence of Mg, or a high concentration of Mg, diminishes the effects of high K concentration or of electrical stimuli on brain respiration; and high concentrations of Ca, which block ATPase, inhibit stimulated brain respiration.