Residual force depression in single sarcomeres is abolished by MgADP-induced activation

• Published in: Scientific reports Vol. 5; no. 1; p. 10555
• Main Authors: Trecarten, Neal, Minozzo, Fabio C., Leite, Felipe S., Rassier, Dilson E.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 03.06.2015; Nature Publishing Group
• Subjects: 631/1647/2204; 631/443; 631/57; Actin; Adenosine Diphosphate - metabolism; Adenosine Diphosphate - pharmacology; Animals; Binding sites; Calcium; Calcium - metabolism; Experiments; Humanities and Social Sciences; Isometric; multidisciplinary; Muscle contraction; Muscle Contraction - physiology; Muscle, Skeletal - drug effects; Muscle, Skeletal - physiology; Myofibrils; Myosin; Needles; Rabbits; Sarcomeres; Sarcomeres - drug effects; Sarcomeres - physiology; Science; Skeletal muscle
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/srep10555

The mechanisms behind the shortening-induced force depression commonly observed in skeletal muscles remain unclear, but have been associated with sarcomere length non-uniformity and/or crossbridge inhibition. The purpose of this study was twofold: (i) to evaluate if force depression is present in isolated single sarcomeres, a preparation that eliminates sarcomere length non-uniformities and (ii) to evaluate if force depression is inhibited when single sarcomeres are activated with MgADP, which biases crossbridges into a strongly-bound state. Single sarcomeres (n = 16) were isolated from rabbit psoas myofibrils using two micro-needles (one compliant, one rigid), piercing the sarcomere externally adjacent to the Z-lines. The sarcomeres were contracted isometrically and subsequently shortened, in both Ca 2+ - and MgADP-activating solutions. Shortening in Ca 2+ -activated samples resulted in a 27.44 ± 9.04% force depression when compared to isometric contractions produced at similar final sarcomere lengths (P  <  0.001). There was no force depression in MgADP-activated sarcomeres (force depression = −1.79 ± 9.69%, P =  0.435). These results suggest that force depression is a sarcomeric property and that is associated with an inhibition of myosin-actin interactions.