Key result
Ca2+ regulates the unloaded shortening velocity in skinned rabbit muscle fibres by reducing the number of crossbridges able to productively bind to the thin filament.
Ca2+ regulates unloaded shortening velocity in skinned muscle fibers by altering the number of active crossbridges rather than modulating crossbridge kinetics.
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Ca2+ sensitivity of shortening velocity informs crossbridge models; leaves open cardiac translation and clinical relevance.
Morris et al. (2003) studied this question. Replacement of native troponin C (TnC) with cardiac TnC (cTnC) or a mixture of cTnC and inactive mutant cardiac TnC (CBMII TnC) vs. Different cTnC:CBMII TnC ratios at saturating [Ca2+] was evaluated on Unloaded shortening velocity. Ca2+ regulates the unloaded shortening velocity in skinned rabbit muscle fibres by reducing the number of crossbridges able to productively bind to the thin filament.
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