ATPase activities in myelin and oligodendrocytes isolated from the brains of developing rats and from bovine brain white matter.

Of the Na,K-ATPase activity in brain homogenates from 20-, 60-, and 120-day-old rats, 1.4 to 2.6% was recovered in myelin. The relative specific activities, at 0.2 to 0.3 times the specific activities in the rat brain homogenates, did not decrease during development, and myelin from bovine brain white matter had a similar relative specific activity. Oligodendrocytes from rat brains and bovine white matter had approximately one third the Na,K-ATPase specific activities found in myelin from the respective sources. The Mg-ATPase activity in rat brain myelin decreased during development and, in myelin from adult rats, was much lower than the Na,K-ATPase activity. Notably, oligodendrocytes from both the forebrains of 10- to 120-day-old rats and from bovine white matter had high Mg-ATPase activities. Whereas Na,K-ATPase may be intrinsic to certain regions of the myelin sheath, the Mg-ATPase in isolated myelin probably arises from fragments of oligodendrocyte membranes.