Comparison of the activities of Na(+),K(+)-ATPase in brains of rats at different ages.

BACKGROUND Na(+),K(+)-ATPase is known to be responsible for the ionic homeostasis in excitable tissues. The energy cost of Na(+),K(+)-ATPase activity is increased in the active brain, so it would be important to ascertain whether defects in brain metabolism in aging are associated with changes in the properties of Na(+),K(+)-ATPase. OBJECTIVE The aim of this study was to investigate the influence of age on the Na(+),K(+)-ATPase activity in developing rat brains from the age of 1 day to 24-28 months. METHODS Crude microsomal preparations were obtained from the brains of newborn (n = 8), 18-day-old (n = 8), 4- to 5-month-old (n = 12), and 24- to 28-month-old (n = 14) rats. Then the ATPase activity was measured and expressed as micromoles of inorganic phosphorus released per milligram of protein per hour. RESULTS The increased tendency in brain Na(+),K(+)-ATPase activity from newborn to 18 days of age suggested that the Na pump is mature soon after birth. No significant differences could be detected in the enzyme activity between newborn and adult rats. In contrast, the Na(+),K(+)-ATPase activity in aged rat brains was found to be significantly lower than in the other age groups of rats tested (p < 0.001). CONCLUSION Our results suggest that aging-induced inhibitions in the brain Na(+),K(+)-ATPase activity may be implicated in the depression of neuronal excitability and in the age-related impairments of cognitive functions.