Actomyosin interaction modulates the resting length of unstimulated cardiac ventricular cells. Sollott, S. J., B. D. Ziman, D. M. Warshaw, H. A. Spurgeon, and E. G. Lakatta. The Laboratory of Cardiovascular Science, Gerontology Research Center, National Institute on Aging, Baltimore, Maryland, _The Department of Medicine, Division of Cardiology, Johns Hopkins Medical Institutions, Baltimore, Maryland, and The Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont
APStracts 3:0075H, 1996.
We sought to determine whether resting or diastolic cardiac myocyte length during low stimulation rates is regulated by myofilament interaction. Cytosolic Ca2+ (Cai, via indo-1 fluorescence) and length, in the presence and absence of 2,3-butanedione monoxime (BDM), a potent inhibitor of force production in striated muscle, were measured in rat and guinea-pig cardiac myocytes at rest and following electrical stimulation. In tetanized cells BDM reduced steady contraction amplitudes for a given Cai. In an actomyosin sliding filament assay without Ca2+ or regulatory proteins, BDM decreased actin filament velocity along myosin. BDM increased both diastolic and resting cell lengths without changes in Cai. The resting cell length also increased when Cai was reduced by removing extracellular Ca2+, an effect further enhanced by BDM and by loading cells with the intracellular Ca2+ chelator, BAPTA-AM. Thus, myofilament interaction is present in cardiac cells, both at rest or during low rates of stimulation, and this myofilament interaction is regulated, in part, by the ambient Cai. 

Received 21 June 1995; accepted in final form 7 February 1996.
APS Manuscript Number H565-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 24 February 96