ATP-induced reconfiguration of the micro-viscoelasticity of cardiac and skeletal myosin solutions

TL;DR

This study investigates how ATP influences the micro-mechanical properties of cardiac and skeletal myosin solutions, revealing significant changes in viscoelastic behavior that relate to muscle function and potential disease mechanisms.

Contribution

It demonstrates ATP-induced reconfiguration of myosin suspensions' micro-mechanics, highlighting differences between cardiac and skeletal muscle responses and their underlying biochemical factors.

Findings

Myosin suspensions become viscoelastic fluids with ATP addition.

Cardiac and skeletal myosin show different stress relaxation times and elastic moduli.

Distinct cooperative behaviors of myosin heads influence mechanical responses.

Abstract

We study the high-frequency micro-mechanical response of suspensions composed by cardiac and skeletal muscle myosin by optical trapping interferometry. We observe that in low ionic strength solutions upon the addition of magnesium adenosine triphosphate (\ch{MgATP^2-}), myosin suspensions radically change their micro-mechanics properties, generating a viscoelastic fluid characterized by a complex modulus similar to a suspension of worm-like micelles. This transduction of energy, from chemical to mechanical, may be related to the relaxed states of myosin, which regulate muscle contractility and can be involved in the etiology of many myopathies. Within an analogous generic mechanical response, cardiac and skeletal myosin suspensions provide different stress relaxation times, elastic modulus values, and characteristic lengths. These discrepancies probably rely on the dissimilar physiological functions of cardiac and skeletal muscle, on the different MgATPase hydrolysis rates of cardiac and skeletal myosins, and on the observed distinct cooperative behavior of their myosin heads in the super-relaxed state. \textit{In vitro} studies like these allow to understand the foundations of muscle cells mechanics on the micro-scale, and may contribute to the engineering of biological materials whose micro-mechanics can be activated by energy regulators.