Adaptation of the skeletal muscle calcium release mechanism to
weight bearing condition.
Kandarian, Susan C., David G. Peters, Terence G. Favero*, Christopher
W. Ward, and Jay H. Williams.
Department of Health Sciences, Boston University, Boston, MA 02215,
Department of Biology, University of Portland, Portland, OR 97203,
Department of Human Nutrition & Foods, Virginia Tech, Blacksburg,
VA 24061
APStracts 2:0440C, 1995.
In the present study we examined whether weight bearing condition can
regulate the SR Ca2+ release mechanism. Measurement of [alpha]1
-subunit dihydropyridine (DHP) and ryanodine receptor levels were made
in hypertrophied fast plantaris muscles 5 wks after surgical removal
of synergist muscles (increased weight bearing) and in atrophied slow
soleus muscles (14 days non-weight bearing) of the rat. Rates of
AgNO3-induced SR Ca2+ release were measured using fura-2 as the Ca2+
indicator and pyrophosphate as the precipitating ion during vesicular
Ca2+ loading. Ca2+ release rates were 38, 49, and 58% lower in
vesicles from hypertrophied vs. control muscles at 0.05, 0.5, and
5[mu]M [AgNO3], respectively (con= 18.2 +/- 1.4[mu]M/mg/min. Western
blots of showed no differences in the relative expression of
[alpha]1DHP or ryanodine receptor using IIID5 (monoclonal) and GP3
(polyclonal) antibodies. There was also no difference in ryanodine
(10nM) binding in Ca2+-incubated SR vesicles from hypertrophied
muscles suggesting no difference in the number of channels. In
contrast, expression of [alpha]1DHP and ryanodine receptor was
increased by 144 and 157% in non-weight bearing soleus muscles.
Scatchard analysis of DHP binding showed a 40% increase in Bmax and
no change in Kd with non-weight bearing. The direction of
modification of the SR calcium release mechanism is opposite with
increased and decreased weight bearing but the mechanism by which
this is achieved appears to be different.
Received 10 August 1995; accepted in final form 1 December 1995.
APS Manuscript Number C493-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 12 December 95