An X-Ray diffraction study on mouse cardiac cross-bridge function in vivo: effects of adrenergic {beta}-stimulation.
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. To our knowledge, 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 approximately 50 ms 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 approximately 90 ms from a diastolic value of 37.2 nm to a maximum of 39.1 nm, and then returned to the diastolic level, corresponding to approximately 10% stretch of sarcomere. Stimulation of beta-adrenergic receptor by dobutamine (20 microg/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 degrees C, showing that the majority of cross-bridges have been recruited with few in reserve.
Toh
Ryuji
R
Division of Cardiovascular and Respiratory Medicine, Department of Internal Medicine, Kobe University Graduate School of Medicine, Kobe 650-0017, Japan.
Shinohara
Masakazu
M
Takaya
Tomofumi
T
Yamashita
Tomoya
T
Masuda
Shigeru
S
Kawashima
Seinosuke
S
Yokoyama
Mitsuhiro
M
Yagi
Naoto
N
D000199:Actins / Q000502:physiology* / Q000648:ultrastructure*; D000318:Adrenergic beta-Agonists / Q000008:administration & dosage; D000818:Animals; D004280:Dobutamine / Q000008:administration & dosage*; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D009218:Myosins / Q000502:physiology* / Q000648:ultrastructure*; D011487:Protein Conformation / Q000187:drug effects; D014961:X-Ray Diffraction / Q000379:methods
D000199:Actins; D000318:Adrenergic beta-Agonists; D004280:Dobutamine; D009218:Myosins