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(Circulation. 2004;109:2976-2979.)
© 2004 American Heart Association, Inc.

Brief Rapid Communications

In Situ Measurements of Crossbridge Dynamics and Lattice Spacing in Rat Hearts by X-Ray Diffraction

Sensitivity to Regional Ischemia

James T. Pearson, PhD; Mikiyasu Shirai, MD, PhD; Haruo Ito, PhD; Noriyuki Tokunaga, MD; Hirotsugu Tsuchimochi, PhD; Naoki Nishiura; Daryl O. Schwenke, PhD; Hatsue Ishibashi-Ueda, MD; Ryuichi Akiyama, PhD; Hidezo Mori, MD, PhD; Kenji Kangawa, PhD; Hiroyuki Suga, MD, PhD; Naoto Yagi, PhD

From the National Cardiovascular Center Research Institute, Osaka, Japan (J.T.P., M.S., N.T., H.T., N.N., D.O.S., H.I.-U., H.M., K.K., H.S.); S-I Medico-Tech Co Ltd, Kashiwara, Osaka, Japan (H.I.); Muroran Institute of Technology, Muroran, Japan (R.A.); and SPring-8/JASRI, Sayo, Hyogo, Japan (N.Y.).

Correspondence to Dr James T. Pearson, Cardiac Physiology, National Cardiovascular Center Research Institute, 5-7-1 Fujishirodai, Suita, Osaka 565-8565 Japan. E-mail jpearson{at}ri.ncvc.go.jp

Received March 1, 2004; de novo received March 31, 2004; revision received May 6, 2004; accepted May 6, 2004.

Background— Synchrotron radiation has been used to analyze crossbridge dynamics in isolated papillary muscle and excised perfused hearts with the use of x-ray diffraction techniques. We showed that these techniques can detect regional changes in rat left ventricle contractility and myosin lattice spacing in in situ ejecting hearts in real time. Furthermore, we examined the sensitivity of these indexes to regional ischemia.

Methods and Results— The left ventricular free wall of spontaneously beating rat hearts (heart rate, 290 to 404 bpm) was directly exposed to brief high-flux, low-emittance x-ray beams provided at SPring-8. Myosin mass transfer to actin filaments was determined as the decrease in reflection intensity ratio (intensity of 1,0 plane over the 1,1 plane) between end-diastole and end-systole. The distance between 1,0 reflections was converted to a lattice spacing between myosin filaments. We found that mass transfer (mean, 1.71±0.09 SEM, n=13 hearts) preceded significant increases in lattice spacing (2 to 5 nm) during systole in nonischemic pericardium. Left coronary occlusion eliminated increases in lattice spacing and severely reduced mass transfer (P<0.01) in the ischemic region.

Conclusions— Our results suggest that x-ray diffraction techniques permit real-time in situ analysis of regional crossbridge dynamics at molecular and fiber levels that might also facilitate investigations of ventricular output regulation by the Frank-Starling mechanism.

Key Words: ischemia • myocardial contraction • myosin • radiography

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