Comparison of calcium loading and retention in isolated skeletal
muscle triads and terminal cisternae.
Kramer, James W., and Adrian M. Corbett.
Department of Biochemistry and Molecular Biology, Wright State
University; Dayton Ohio 45435
APStracts 2:0436C, 1995.
Calcium loading and retention were examined in isolated skeletal
muscle triads and terminal cisternae to determine: 1) if excessive
loading altered the response of triads to depolarization induced
calcium release and 2) if these vesicles were similar in their
ability to load and retain calcium. A mixture of triads and terminal
cisternae was loaded with variable amounts of calcium and then
subjected to maximal depolarization. Calcium release was monitored by
changes in extravesicular fura-2 fluorescence using 340/380 nm
excitation and 510 nm emission wavelengths. The amount of calcium
released from triads due to maximal depolarization increases with
increasing calcium loads until a maximal response is obtained,
indicating triad saturation. At pH 7, triadic vesicles preferentially
loaded and retained calcium at low calcium loads, but, with
increasing loads, non-triadic vesicles began to retain calcium. At pH
6.5, which should close all open uncoupled ryanodine receptors,
triadic and isolated terminal cisternae vesicles loaded and retained
calcium in a similar manner. A population of triads, which have some
uncoupled ryanodine receptors, did not retain their loaded calcium at
pH 7.0, but did retain calcium at pH 6.5: this resulted in a doubling
of the amount of calcium released upon maximal depolarization after
loading at pH 6.5.
Received 28 June 1995; accepted in final form 27 November 1995.
APS Manuscript Number C387-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 12 December 95