D. Danielibetto et al., EFFECTS OF AGE ON SARCOPLASMIC-RETICULUM PROPERTIES AND HISTOCHEMICALCOMPOSITION OF FAST-AND SLOW-TWITCH RAT MUSCLES, Acta Physiologica Scandinavica, 154(1), 1995, pp. 59-64
Calcium release activity of sarcoplasmic reticulum and enzyme-histoche
mical properties were investigated in extensor digitorum longus (e.d.l
.) and soleus muscles in young (4 months) and old (24 months) male rat
s. With age, the caffeine threshold concentration for calcium release
from the sarcoplasmic reticulum of soleus skinned muscle fibres showed
only minor modifications. On the other hand, in e.d.l. skinned muscle
fibres, the caffeine threshold concentration decreased significantly
(P < 0.05). The histochemical fibre type composition changed with age
both in soleus and in e.d.l. muscles, showing a common transformation
toward a more oxidative histochemical profile. In fact, in aged soleus
, a significant (P < 0.05) increase was observed of type 1 fibres to r
epresent almost the totality of the muscle fibres (more than 98%), whi
le types 2C and 2A were reduced in proportion. In aged e.d.l. the perc
entage of type 1 (P < 0.05), 2A and 2X (a recently identified fourth c
omponent of the fast-twitch muscle types) fibres increased, with a red
uction of type 2B (P < 0.01) fibres. The present results suggest that
the changes in contractile properties of aged muscles may be related t
o the changes not only in fibre composition but also in the mechanism
of calcium release from sarcoplasmic reticulum.