In rat cardiac muscle, 80% of myosin heads transferred to the thin filament during maximum isometric contraction at pCa 4.4, with disproportionately large transfer at low calcium concentrations.
In rat cardiac muscle, a significant fraction of myosin heads transfer to thin filaments at low calcium concentrations without producing tension.
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 et al. (Sun,) reported a other. Calcium concentration was evaluated on Transfer of myosin heads from thick to thin filaments. In rat cardiac muscle, 80% of myosin heads transferred to the thin filament during maximum isometric contraction at pCa 4.4, with disproportionately large transfer at low calcium concentrations.