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Biophys. J. BioFAST: First Published December 9, 2005. doi:10.1529/biophysj.105.074062
© 2005 by the Biophysical Society.

A more recent version of this article appeared on March 1, 2006.
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MUSCLE AND CONTRACTILITY

An X-ray Diffraction Study on Mouse Cardiac Cross-Bridge Function in vivo : Effects of Adrenergic {beta}-stimulation

Ryuji Toh 1, Masakazu Shinohara 1, Tomofumi Takaya 1, Tomoya Yamashita 1, Shigeru Masuda 1, Seinosuke Kawashima 1, Mitsuhiro Yokoyama 1 and Naoto Yagi 2*

1 Kobe University Graduate School of Medicine
2 JASRI, SPring-8

* To whom correspondence should be addressed. E-mail: yagi{at}spring8.or.jp.

Submitted on September 8, 2005
Revised on October 17, 2005
Accepted on 18 November 2005


  Abstract
In order to investigate how {beta}-stimulation affects the contractility of cardiac muscle, x-ray diffraction from cardiac muscle in the left ventricular free wall of a mouse heart was recorded in vivo. This is the first x-ray diffraction study on a heart in a living body. After the R-wave in electrocardiograms, the ratio of the intensities of the equatorial (1,0) and (1,1) reflections decreased for about 50 msec from a diastolic value of 2.1 to a minimum of 0.8, and then recovered. The spacing of the (1,0) lattice planes increased for about 90 msec from a diastolic value of 37.2 nm to a maximum of 39.1 nm, and then returned to the diastolic level, corresponding to about 10% stretch of sarcomere. Stimulation of {beta}-adrenergic receptor by dobutamine (20 µg/kg/min) accelerated both the decrease in the intensity ratio, which reached a smaller systolic value, and the increase in the lattice spacing. However, the intensity ratio and spacing at the end-diastole were unchanged. The recovery of the lattice spacing during relaxation was also accelerated. The mass transfer to the thin filaments at systole in a {beta}-stimulated heart was close to the peak value in twitch of frog skeletal muscle at 4 °C, showing that the majority of cross-bridges have been recruited with few in reserve.

Key Words: adrenergic beta-stimulation, myosin cross-bridge, x-ray diffraction




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Copyright © 2005 by the Biophysical Society.