Decrease in regucalcin level and enhancement of protein tyrosine phosphatase activity in rat brain microsomes with increasing age.

The role of regucalcin, a regulatory protein in Ca2+ signaling, in the microsomes of brain tissue in rats has not been clarified so far. Western blot analysis showed that regucalcin was present in the brain microsomes. Regucalcin levels were significantly decreased in the brain microsomes obtained from 50-week-old rats as compared with that of 5-week-old rats. Meanwhile, protein tyrosine phosphatase activity was seen in the brain microsomes. The enzyme activity was significantly increased with increasing age. The presence of regucalcin (10(-9) M) in the enzyme reaction mixture containing the brain microsomes obtained from 50-week-old rats caused a significant decrease in protein tyrosine phosphatase activity. Such a decrease was not seen in the brain microsomes from 5-week-old rats. Moreover, the presence of anti-regucalcin monoclonal antibody (10 ng/ml) in the enzyme reaction mixture containing the brain microsomes from young and aged rats caused a significant increase in protein tyrosine phosphatase activity, indicating a suppressive role of microsomal endogenous regucalcin. The present study demonstrates that regucalcin is present in the brain microsomes, and that its level is decreased with increasing age. This decrease may be partly involved in the enhancement of protein tyrosine phosphatase activity in the brain mirosomes with increasing age.