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Originally published as Biophys J. BioFAST on February 9, 2007.
doi:10.1529/biophysj.107.104257
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Biophysical Journal 92:L73-L75 (2007)
© 2007 The Biophysical Society

Interfilament Spacing Is Preserved during Sarcomere Length Isometric Contractions in Rat Cardiac Trabeculae

Gerrie P. Farman *, Edward J. Allen *, David Gore {dagger}, Thomas C. Irving {dagger} and Pieter P. de Tombe *

* Center for Cardiovascular Research, Department of Physiology and Biophysics, University of Illinois College of Medicine, Chicago, Illinois 60612-7342; and {dagger} Department of Biological, Chemical, and Physical Sciences, Illinois Institute of Technology, Chicago, Illinois 60616

Correspondence: Address reprint requests and inquiries to Pieter P. de Tombe, E-mail pdetombe{at}uic.edu.

It is generally assumed that the myofilament lattice in intact (i.e., nonskinned) striated muscle obeys constant volume. However, whether such is the case during the myocardial contraction is unknown. Accordingly, we measured interfilament spacing by x-ray diffraction in ultra-thin isolated rat right ventricular trabeculae during a short 10 ms shuttered exposure either just before electrical stimulation (diastole), or at the peak of the contraction (systole); sarcomere length (SL) was held constant throughout the contraction using an iterative feedback control system. SL was thus varied in a series of SL-clamped contractions; the relationship between SL and interfilament spacing was not different between diastole and systole within 1%; this was true also over a wide range of inotropic states induced by varied [Ca2+]o. We conclude that the cardiac myofilament lattice maintains constant volume, and thus constant interfilament spacing, during contraction.




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