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 sodium ion concentration of the medium and is independent of whether choline chloride or sucrose is used to balance diminished levels of sodium ions. Choline, in contrast to sucrose, resembles sodium in the maintenance of stimulated brain respiration but cannot replace sodium for the stimulation of brain respiration by electrical impulses or by increased potassium ion concentrations. Electrical stimulation of rat brain slices, whilst resembling potassium stimulation in causing a fall in the level of ATP, differs from potassium stimulation in causing no diminution in the rate of glycine transport. This is considered to be due to the operation of two opposing processes: (a) increased glycine influx due to increased influx of sodium, and (b) 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 potassium ion 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 following facts, (a) The presence of potassium ions is needed to obtain the optimal respiratory responses and the optimal rate of glycine uptake; (b) ouabain inhibits the influx of glycine whether the brain tissue is in the stimulated condition or not and it also inhibits stimulated brain respiration; (c) absence of magnesium ions, or a high concentration of magnesium ions, diminishes the effects of high potassium ion concentration or of electrical stimuli on brain respiration; and (d) high concentrations of calcium ions, which block ATPase, inhibit stimulated brain respiration.