Key result
The velocity of a regulated thin filament at a saturating calcium concentration (pCa 4) exceeded that of a nonregulated thin filament by 65% and 87% for skeletal and cardiac myosin, respectively.
Why the study?
The calcium-mechanical relationship in skeletal and cardiac muscles using in vitro motility assays with regulated contractile systems was investigated to understand differences in contractile regulation.
The study demonstrates differences in the calcium-mechanical relationship and cooperativity mechanisms between skeletal and cardiac muscles using an in vitro motility assay.
Answers are grounded in this paper and cite their sources.
Indicates stronger thin-filament cooperativity for cardiac than skeletal myosin; leaves open translation to intact muscle or human physiology.
In a set of experiments on regulated contractile systems (i.e., in vitro motility assay with a reconstructed thin filament), the velocity of a thin filament on the surface coated with rabbit skeletal or rat cardiac myosin was estimated at various calcium ion concentrations in solution (pCa 4–8). The velocity versus pCa curve proved to be sigmoid. The velocity of a regulated thin filament at a saturating calcium concentration (pCa 4) exceeded that of a nonregulated thin filament by 65 and 87% for skeletal and cardiac myosin, respectively. The Hill coefficient was 1.95 and 2.5 for skeletal and cardiac muscles, respectively; this difference was discussed in terms of the different contributions of cooperativity mechanisms of contractile and regulatory proteins to the regulation of contraction in these types of muscle.
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Kopylova et al. (2006) studied this question. Calcium ion concentration (pCa 4-8) vs. Nonregulated thin filament was evaluated on Velocity of a thin filament. The velocity of a regulated thin filament at a saturating calcium concentration (pCa 4) exceeded that of a nonregulated thin filament by 65% and 87% for skeletal and cardiac myosin, respectively.
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