Effects of aging on calcium pump activity of sarcoplasmic reticulum
and twitch duration in gastrocnemius and soleus muscles of the
fischer 344 rat.
Narayanan, N., D. L. Jones, A. Xu, and J. C. Yu.
Department of Physiology, The University of Western Ontario,
London, Ontario, Canada N6A 5C1
APStracts 3:0141C, 1996.
The impact of aging on the Ca2+ pump function of skeletal muscle
sarcoplasmic reticulum (SR) was investigated using SR-enriched
membrane vesicles isolated from the slow-twitch soleus muscle (SM)
and the relatively fast-twitch gastrocnemius muscle (GM) isolated
from adult (6-8 months old) and aged (26-28 months old) Fischer 344
rats. In addition, isometric twitch characteristics of SM and GM were
determined in situ in adult and aged rats under anaesthesia. The
rates of ATP-supported Ca2+ uptake by SMSR was markedly lower (50%)
in the aged compared to adult at varying Ca2+ (0.11 - 8.24 [mu]M)
concentrations. Kinetic analysis of the data revealed age-associated
decrease in Vmax and increase in K0.5 for Ca2+. In contrast, no
significant age-related difference was observed in ATP-supported Ca2+
uptake activity of GMSR. The Ca2+-stimulated ATPase activities and
the amount of Ca2+-ATPase protein did not vary significantly with
aging in SMSR or GMSR. Also, no significant age-related difference
was observed in the content of ryanodine receptor (Ca2+-release
channel) or the Ca2+-binding protein, calsequestrin in SMSR and GMSR.
In isometrically contracting SM, the time to peak force, half
-relaxation time and contraction duration were significantly prolonged
in the aged compared to adult whereas there was no age-related
difference in maximum developed force. None of these isometric twitch
parameters differed significantly with age in the GM. These results
demonstrate that the effects of aging on skeletal muscle contractile
properties and SR function are muscle-specific. Furthermore, the data
suggest strongly that impairment in SR Ca2+ pump function, apparently
due to uncoupling of ATP hydrolysis from Ca2+ transport, contributes
to the age-associated slowing of relaxation in the soleus muscle.
Received 1 September 1995; accepted in final form 18 April 1996.
APS Manuscript Number C539-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 May 96