Effects of tissue fractionation on exercise-induced alterations in
sarcoplasmic reticulum function in rat gastrocnemius muscle.
Chin, Eva R., and Howard J. Green.
Department of Kinesiology, University of Waterloo, Waterloo,
Ontario N2L 3G1 CANADA
APStracts 2:0515A, 1995.
Since studies into exercise-induced alterations in sarcoplasmic
reticulum (SR) Ca2+-sequestration have produced conflicting reports,
we have hypothesized that the differences in SR Ca2+ ATPase activity
and Ca2+ uptake in SR fractions observed in different studies is due
to different SR isolation techniques. To investigate this
possibility, rat white (WG) and red (RG) gastrocnemius muscle from
control and run animals were studied using two conventional isolation
techniques to obtain a crude microsomal (CM) fraction and an isolated
SR vesicle (SRV) fraction. Indices of CM and SRV function were
compared to measurements from whole muscle homogenate (HOM).
Treadmill running to exhaustion did not alter SR protein yields, % SR
extraction, basal or Ca2+ ATPase purification in either fraction.
Ca2+-activated ATPase activity was not altered by exercise in any of
the fractions examined but Ca2+ uptake was reduced in HOM (9.48 +/-
1.4 to 6.90 +/- 0.8 nmol x mg-1 .min-1) and SRV (84.0 +/- 11.5 to
50.7 +/- 14.0 nmol x mg-1 x min-1) from RG at free [Ca2+] of 600
-700nM. These data indicate that reductions in SR Ca2+ uptake are
dissociated from changes in Ca2+ ATPase in vitro and occur only in a
specific population of vesicles. The mechanisms underlying these
alterations are not known, but may involve a reduction in the number
of Ca2+ ATPase enzymes or a selective sedimentation of damaged
vesicles in the SRV fraction.
Received 4 April 1995; accepted in final form 6 October 1995.
APS Manuscript Number A374-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95