Carbonic Anhydrase, 5′‐Nucleotidase, and 2′,3′‐Cyclic Nucleotide‐3′‐Phosphodiesterase Activities in Oligodendrocytes, Astrocytes, and Neurons Isolated from the Brains of Developing Rats

The activities of three myelin‐associated enzymes, carbonic anhydrase, 5′‐nucleotidase, and 2′,3′‐cyclic nucleotide‐3′‐phosphodiesterase (CNP), were measured in oligodendrocytes, neurons, and astrocytes isolated from the brains of rats 10, 20, 60, and 120 days old. The carbonic anhydrase specific activity in oligodendrocytes was three‐ to fivefold higher than that in brain homogenates at each age, and, at all the ages, low activities of this enzyme were measured in neurons and astrocytes. The oligodendrocytes and astrocytes from the brains of rats at all ages had higher activities of the membrane‐bound enzyme 5′‐nucleotidase than was observed in neurons. In oligodendrocytes from 10‐ and 20‐day‐old rats, the 5′‐nucleotidase activity was two‐ to threefold the activity in the homogenates (i.e., relative specific activity = 2.0–3.0), and the relative specific activity of this enzyme in the oligodendrocytes declined to less than 1.0 at the later ages, concomitant with the accumulation of 5′‐nucleotidase in myelin. The CNP activity was always higher in oligodendrocytes than in neurons, but not appreciably different from that in astrocytes from 20 days of age onward. The relative specific activity of CNP was highest in the oligodendrocytes from 10‐day‐old rats but was lower, at all ages, than we had observed in bovine oligodendrocytes. These enzyme activities in oligodendroglia are quite different in amount and developmental pattern from those reported previously for myelin.