Effects of ouabain, glutamate and cations on phosphate incorporation in brain slices

Abstract

Guinea-pig brain cortex slices were incubated in media in which the concentrations of sodium, potassium, calcium, glutamate and ouabain were varied, and the absolute levels and rate of phosphate incorporation into ATP and 5 acid-insoluble phosphate fractions were measured. The level of inorganic phosphate and of the acid-insoluble phosphate fractions, except for phosphoprotein, did not vary significantly under different conditions. ATP levels were lowered by ouabain, glutamate or omission of sodium from the medium. The rate of phosphate incorporation into all acid-insoluble phosphate fractions was lowered by 75% when sodium was replaced by choline and by 60% by glutamate. Incorporation was stimulated by 35% by the omission of calcium from the medium and by up to 20% on raising the potassium concentration from 2.5 to 7.5 mM, except for phospholipid, incorporation into which was reduced by 35% by raised potassium. Ouabain at 10 μM caused a 35% inhibition of incorporation in the sodium medium in both rat and guinea-pig cortex slices. Lower concentrations of ouabain gave smaller inhibitions. The rise in incorporation caused by omission of calcium and the fall caused by glutamate, were abolished by ouabain. The fall in incorporation into phospholipid, and the rise in all other acid-insoluble fractions, caused by raised potassium, were both reversed by ouabain. All effects of glutamate, calcium and ouabain were abolished when sodium was replaced by choline.