Na<SUP>+</SUP>-K<SUP>+</SUP>ATPase in Human Brain Tumors

Na+-K+-stimulated adenosine triphosphat s (Na+-K+ATPase) activities were measured in 12 human brain tumors and surrounding tissue (white matter and cortex) by the colorimetric deter mination of hydrolyzed inorganic phosphorus (Pi) from adenosine triphosphate (ATP). In glioma cases, the brain microvessels, filial component, and neurons were isolated from the cortex by the methods of Brendel, et al., and Nagata, et al. n each sample, Na+-K+ATPase activity was measured in the presence of various K+ ion concentrations. &nbsp; In 8 glioma cases, the lowest value was obtained in the glioblastoma multiforme. Decrease in Na+K+ATPase activity in the tumor or in the surrounding tissue was roughly proportional to the pathological malignancy of the tumor. In 2 cases of glioma with an epileptic focus shown by elec troencephalography, activity of the enzyme was decreased in the epileptic cortex. In one case of glioma without epileptic focus, decrease of the enzyme activity was mainly attributed to decrease in the glial component. The kinetic parameters, maximum velocity (Vmax) and activation constant for K+ (Ka) were also calculated in each sample to determine the effect of the K+ ion on the Na+K+ATPase activity. Vmax in the tumor region was significantly decreased compared with the sur rounding tissue. On the other hand, differences in Ka were not so significant. Disturbed buffering action for the extracellular K+ ions observed in the glioma group might result in lowered ability to maintain the electrolytic milieu, and might play a significant role in the development of the epileptic focus.