In vitro K+-effect on ATP and phosphocreatine levels and on Na+ K+-atpase activity of mouse brain cells.

Cell suspensions were prepared form mouse brain cortices. Cells were incubated in a medium also containing 10 mmol.l-1 glucose and either 5 mmol l-1 K+ or 50 mmol.l-1 K+ concentration. In order to standardize individual experiments, the biuret reaction was modified for rapid determination of the protein in cell suspensions. The cellular reserves of energy-rich phosphates were determined in the course of 60 min of cell incubation with 5 mmol.l-1 K+ and following 30 min incubation of cells with 50 mmol.l-1 K+. The level of ATP was significantly elevated after 10-60 min of incubation with low K+, from 0.58 to 0.78 micromoles per 100 mg protein; the creatine phosphate content during the same interval was in the range 1.27-1.44 micromoles per 100 mg protein. A significant decrease of energy reserves in cells was observed if the extracellular concentration of K+ was increased. After 10 and 30 min of incubation, a decrease by 36.2% and 38.5% for creatine phosphate and 34.6% and 44.9% for ATP was found, respectively. Na+ K+-ATPase activity of cells incubated for 60 min with 5 mmol.l-1 K+ was expressed as 4.99 micromoles of liberated Pi per 100 mg protein.1 h. Enzyme activity was stimulated with 50 mmol.l-1 K+ by 24.3% and 25.7% after 10 and 30 min of cell incubation respectively. Stimulation of Na+ K+-ATPase activity of brain cortex cells was directly dependent on the actual presence of stimulating 50 mmol.l-1 K+ concentration.