In situ measurements of crossbridge dynamics and lattice spacing in rat hearts by x-ray diffraction: sensitivity to regional ischemia.
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.


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.
Pearson
James T
JT
Cardiac Physiology, National Cardiovascular Center Research Institute, 5-7-1 Fujishirodai, Suita, Osaka 565-8565 Japan. jpearson@ri.ncvc.go.jp
Shirai
Mikiyasu
M
Ito
Haruo
H
Tokunaga
Noriyuki
N
Tsuchimochi
Hirotsugu
H
Nishiura
Naoki
N
Schwenke
Daryl O
DO
Ishibashi-Ueda
Hatsue
H
Akiyama
Ryuichi
R
Mori
Hidezo
H
Kangawa
Kenji
K
Suga
Hiroyuki
H
Yagi
Naoto
N
D008841:Actin Cytoskeleton / Q000737:chemistry / Q000648:ultrastructure; D000205:Actomyosin / Q000737:chemistry / Q000648:ultrastructure; D000818:Animals; D003199:Computer Systems; D006321:Heart / Q000528:radiation effects; D006352:Heart Ventricles / Q000737:chemistry; D008297:Male; D009200:Myocardial Contraction; D017202:Myocardial Ischemia / Q000378:metabolism / Q000503:physiopathology; D009206:Myocardium / Q000737:chemistry* / Q000648:ultrastructure; D009218:Myosins / Q000737:chemistry* / Q000648:ultrastructure; D010210:Papillary Muscles / Q000737:chemistry / Q000648:ultrastructure; D011487:Protein Conformation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012518:Sarcomeres / Q000737:chemistry / Q000648:ultrastructure; D017356:Synchrotrons; D016276:Ventricular Function; D014961:X-Ray Diffraction
D000205:Actomyosin; D009218:Myosins