Fine-tuning striated muscle performance: conserved sarcomere-level mechanisms across insect and vertebrate systems

Figures

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  Figure 1. Mechanical and calcium signaling differences between synchronous and asynchronous insect flight muscle. Schematic comparison of synchronous (left panel) and asynchronous (right panel) insect flight muscle highlighting differences in neural coupling, mechanical activation, and calcium dynamics. In synchronous muscle, each motor neuron impulse generates a discrete Ca2+ transient that activates the troponin-tropomyosin complex, producing a single contraction-relaxation cycle and a 1:1 relationship between neural input and mechanical output. Contraction is directly coupled to Ca2+ cycling. In contrast, asynchronous indirect flight muscle (IFM) operates at sustained, permissive Ca2+ levels that maintain partial activation of the contractile apparatus. Low-frequency neural input initiates oscillatory contractions maintained through stretch activation, in which thoracic deformation mechanically activates antagonistic muscles. Phasic Ca2+ spikes in synchronous muscle contrast with tonic priming Ca2+ levels in asynchronous IFM, enabling high-frequency, energy-efficient contraction. Created in BioRender. Sujkowski, A. (2026) https://BioRender.com/ntbo1ok.

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  Figure 2. A conserved sarcomere-level mechanism underlies oscillatory power in IFM and length-dependent activation in cardiac muscle. Lengthening strain increases the fraction of force-generating cross-bridges within evolutionarily conserved sarcomeric architectures (depicted as increased density of attached heads). Z-disc separation indicates increased sarcomere length. In insect indirect flight muscle (IFM), cyclic stretch-shortening modulates cross-bridge recruitment during each oscillation, amplifying power output. In cardiac muscle, increased diastolic length (preload) enhances systolic force through length-dependent activation (Frank-Starling mechanism). The underlying strain-sensitive principle is shared, but its physiological deployment differs.