Key result
Direct observation of individual cardiac thin filaments at systolic Ca2+ levels revealed stochastic activation with short-range cooperativity evident on only one strand.
Why the study?
The structure of the thin filament at physiological Ca 2+ levels is unknown, limiting the understanding of thin filament regulation by Ca 2+.
Provides structural insights into how cardiac muscle is regulated by a narrow range of Ca2+ levels during the transition from diastole to systole.
Answers are grounded in this paper and cite their sources.
Stochastic thin filament activation at systolic Ca2+ may refine Ca2+ sensitivity models; leaves open validation in intact myocytes.
Significance Heartbeats rely on cyclical interactions between myosin thick and actin thin filaments orchestrated by rising and falling Ca 2+ . During systole, Ca 2+ binds to the thin filament and allows its interaction with the thick filament to produce force required for contraction. The structure of the thin filament at physiological Ca 2+ levels is unknown, which limits our understanding of the thin filament regulation by Ca 2+ . Here, we directly observe thin filament structural states along individual filaments at systolic Ca 2+ levels to show that the thin filament is activated stochastically with short-range cooperativity evident only on one strand of the thin filament. We suggest how cardiac muscle can be regulated by a narrow range of Ca 2+ levels upon transition from diastole to systole.
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Risi et al. (2021) studied this question. Systolic Ca2+ levels was evaluated on Thin filament structural states. Direct observation of individual cardiac thin filaments at systolic Ca2+ levels revealed stochastic activation with short-range cooperativity evident on only one strand.
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