Alkaline phosphatase activity in striated muscle: the effect of aging and long-term training in female mice

Alkaline pNPPase (Alk'ase) activity was measured in bicarbonate buffer and in Triton buffer of striated muscles of aging mice. Between young age (4-9 months) and middle age (13-15 months) the enzyme specific activity increased by 41.8% in the bicarbonate buffer and by 22.6% in the Triton extraction. Thereafter, between middle age and old age (32 months), a marked decrease in enzyme activity took place in both the bicarbonate and Triton extractions (23.5% and 31.4%, respectively). Alk'ase activity in muscles of old mice that had been exposed for prolonged training (12-18 months), did not differ from that of age-matched controls in both types of extracts. However, cysteine, an Alk'ase inhibitor, affected the enzymatic activity in the various samples tested differently: in the bicarbonate buffer its inhibitory effect increased with age and training, whereas in the Triton extraction its effect decreased with age and following training. Thus, it seems conceivable that with age and following long-term physical exercise an overall functional change is taking place in muscle which makes Alk'ase more vulnerable. The membranous Alk'ase, however, appears more resistant to external inhibitors in the form of endurance training and to the aging process.