Cross-bridge movement in rat cardiac muscle as a function of calcium concentration.
1. By applying the X-ray diffraction method to chemically skinned papillary muscles of the rat, the transfer of myosin heads from the thick to the thin filaments was studied as a function of Ca2+ concentration. 2. No significant transfer of the heads occurred when the Ca2+ concentration was below the threshold of contraction (pCa 6.2). 3. During the maximum isometric contraction at pCa 4.4, 80% of the myosin heads were transferred to the thin filament. 4. When the muscle was activated isometrically at low Ca2+ concentrations (pCa 6.2-5.8), where the average tension was less than 20% of the maximum, a disproportionately large number of myosin heads were transferred to the thin filament. 5. It was concluded that a significant fraction of the heads transferred at the low Ca2+ concentrations does not produce tension.
Matsubara
I
I
Department of Pharmacology, University of Tohoku School of Medicine, Sendai, Japan.
Maughan
D W
DW
Saeki
Y
Y
Yagi
N
N
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000502:physiology; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism*; D009218:Myosins / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains
D009218:Myosins; D002118:Calcium