A critical evaluation of resting intracellular free calcium regulation in dystrophic mdx muscle. Hopf, F. Woodward, Paul R. Turner, Wilfred F. Denetclaw, Jr., Praveen Reddy, and Richard A. Steinhardt. Cell and Developmental Biology, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3200 U.S.A.
APStracts 3:0119C, 1996.
There are conflicting reports regarding whether resting free calcium levels ([Ca2+]i) are elevated in dystrophic mouse (mdx) myotubes and adult myofibers. We reinvestigated this question and found several lines of evidence supporting the hypothesis that increased calcium influx via leak channels leads to increases in resting [Ca2+]i. (1) Step calibration of fura-2/free acid in myofibers using microinjected Ca2+-EGTA buffers revealed greater [Ca2+]i in dystrophic cells. Careful calibration of fura-PE3/AM-ester, a compartmentalization -resistant derivative of fura-2, also showed elevated [Ca2+]i in mdx myotubes. (2) Chronic but not acute application of TTX reduced resting [Ca2+]i in dystrophic myotubes, suggesting that elevated resting [Ca2+]i is a consequence of previous long-term contractile activity. (3) Rates of manganese quenching of fura-2 fluorescence, an indirect indicator of calcium influx, were significantly higher in mdx myotubes, and were increased by nifedipine, a calcium leak channel agonist. (4) Calcium leak channel activity, measured using patch-clamping, was greater in the sarcolemma of adult, non-enzyme treated, mdx myofibers. 

Received 24 May 1995; accepted in final form 3 April 1996.
APS Manuscript Number C299-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 23 April 96