INFLUENCE OF CULTURE CONDITIONS ON MONOAMINE-OXIDASE-A AND MONOAMINE-OXIDASE-B ACTIVITY IN RAT ASTROCYTES

Astroglial cells dispersed from newborn rat hemispheres were establish ed in medium supplemented with 20 per cent fetal calf serum (FBS) and then grown to a confluent monolayer in the presence of 10 per cent FBS or charcoal-stripped FBS (CS). Type 1 astrocytes were subcultured and either maintained under the same conditions of the primary cultures o r converted to serum-free chemically defined medium (CDM). No differen ces were found in either MAO A or MAO B activity of astrocytes grown i n the presence of FBS or CS after 15 and 21 days in vitro (day 1 and 6 of subculture). In contrast, on day 21 both MAO A and MAO B activitie s were markedly higher in astrocytes subcultured in CDM compared with cells maintained in serum-supplemented medium. This difference appeare d to be due to increased number of enzyme molecules, since kinetic ana lysis showed an increase in V-max of both MAO isoenzymes in serum-free medium, but no change in K-m. Consistently, the recovery of MAO A and MAO B activity after irreversible enzyme inhibition by clorgyline and deprenyl was faster in CDM than in FBS-supplemented medium, indicatin g enhanced enzyme synthesis under serum-free condition. Estimates of h alf-lives for the recovery of MAO A and MAO B activity indicated that, under both culture conditions, type A activity had a higher turnover rate than type B. The effect of CDM on astrocyte MAO does not appear t o be due to selection of a subpopulation of cells, but rather linked t o a morphological change (differentiation) with increased synthesis of both MAO isoenzymes.