The effect of magnesium and atp on depolarization-induced calcium release
in isolated skeletal muscle triads.
Ritucci, Nick A., and Adrian M. Corbett.
Department of Physiology & Biophysics
APStracts 2:0066C, 1995.
The effect of different free Mg2+ and ATP concentrations on depolarization
-induced calcium release in isolated skeletal muscle triadic vesicles was
examined by simultaneously monitoring direct effects on ryanodine receptors
from either isolated or coupled terminal cisternae. Free Mg2+ was increased
to concentrations of 11-14 [mu]M, 81 [mu]M, 175-181 [mu]M, and 1 mM while:
1) total ATP concentration was kept constant or 2) MgATP concentration was
kept constant. The following was observed: 1) increasing MgATP reduces the
measurable calcium release from isolated vesicles by stimulating the Ca2+
-ATPase in the terminal cisternae; 2) half maximal inhibition of functionally
coupled ryanodine receptors during depolarization-induced calcium release is
observed at 1 mM Mg2+, while half-maximal inhibition of the non-depolarized
ryanodine receptor is seen at 75 [mu]M Mg2+ at the same free ATP and MgATP
concentrations; 3) two separate time constants for calcium release were
obtained for non-depolarized ryanodine receptors when free Mg2+ was 14 [mu]M
and free ATP was 6.1 mM: this may represent triadic ryanodine receptors versus
isolated terminal cisterna ryanodine receptors.
Received 25 July 1994; accepted in final form 3 January 1995.
APS Manuscript Number C433-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 28 February 1995.