Redox Balance Differentially Affects Biomechanics in Permeabilized Single Muscle Fibres—Active and Passive Force Assessments with the Myorobot

Abstract

An oxidizing redox state imposes unique effects on the contractile properties of muscle. Permeabilized fibres show reduced active force generation in the presence of H2O2. However, our knowledge about the muscle fibre’s elasticity or flexibility is limited due to shortcomings in assessing the passive stress–strain properties, mostly due to technically limited experimental setups. The MyoRobot is an automated biomechatronics platform that is well-capable of not only investigating calcium responsiveness of active contraction but also features precise stretch actuation to examine the passive stress–strain behaviour. Both were carried out in a consecutive recording sequence on the same fibre for 10 single fibres in total. We denote a significantly diminished maximum calcium-saturated force for fibres exposed to ≥500 µM H2O2, with no marked alteration of the pCa50 value. In contrast to active contraction (e.g., maximum isometric force activation), passive restoration stress (force per area) significantly increases for fibres exposed to an oxidizing environment, as they showed a non-linear stress–strain relationship. Our data support the idea that a highly oxidizing environment promotes non-linear fibre stiffening and confirms that our MyoRobot platform is a suitable tool for investigating redox-related changes in muscle biomechanics.

Levosimendan’s Effects on Length-Dependent Activation in Murine Fast-Twitch Skeletal Muscle

“…Both untreated control EDL fibres and those incubated in the levosimendan solution display a gradual increase in pCa 50 , with no major difference between both groups. The values ranging from 5.8 to 6.2 compare well with previously published data [ 20 , 39 , 40 ]. Although in LDA Ca 2+ sensitivity increases with SL, the amount of generated force follows a bell-shaped relationship, peaking at an optimum SL between 2.3 µm to 2.5 µm in mice [ 41 ].…”

“…The restoration force/stress in response to stretch will therefore, consistently increase with SL up to rupture [45]. Myofibrils, single fibres, and whole EDL muscle typically produce between ∼40 to 70 kPa passive restoration stress from 3.0 µm to 4.0 µm [40,[46][47][48] which is in agreement with data from our control group; the axial Young's modulus can easily reveal values that are twice of those (E mod = stress strain = 40to70 kPa 0.4 ∼100-200 kPa). This seems plausible given the fact that the Young's modulus of soleus single muscle fibres scales between 400-600 kPa [48] and are considered twice as stiff as EDL single muscle fibres [49].…”

Effects of Adjuvant Exercise and Nutrition Therapy on Muscle Fibre Biomechanics in Gastrointestinal Cancer Patients

“…Such disrupted force transmission might also contribute to compromised active force generation. Nevertheless, real-time assessment of SL during functional recordings was not yet possible with the MyoRobot, at the time of this study, as opposed to more recent studies using an improved MyoRobot 2.0 [37]. A follow-up study addressing this will be conducted in due course.…”