Influence of Sample Source: Sliding Velocity of Different Native Thin Filaments on Tissue Purified Slow Skeletal and Cardiac Myosin

Abstract

Introduction: The muscle myosin uses energy derived from ATP hydrolysis to perform mechanical work and move actin filaments, thereby generating force. The goal of this study was to investigate the force production by isolated myosin filaments at different ATP concentration, using a new system that we developed in our laboratory that allows mechanical measurements and visualization of the filaments simultaneously. We also measured the actomyosin ATPase activity of the filaments to correlate with force. Methods: Two types of myosin filaments were used in this study; smooth myosin filaments were isolated from the ABRM of M. edulis, and skeletal myosin filaments were isolated from rabbit psoas muscles. An experimental chamber was mounted on an inverted microscope with fluorescence imaging. The force produced by the myosin filaments upon interaction with fluorescence actin at four different concentration of ATP, 0.5, 0.75, 1.0 and 1.25mM was calculated using the displacement of the cantilevers of known stiffness. (Kalganov et al., 2013). Mg-ATPase activity was measured using methods previously described (Shelud'ko, et al., 2007). Results and Discussion: Forces in both types of myosin filaments were increased consistently with increasing ATP concentration from 0.5mM to 1.25mM during actomyosin interactions. The force produced by smooth and skeletal muscle myosin filaments were 67.05pN/mm and 54.62pN/mm at 0.5mM ATP, and 103.27pN/mm and 112.51pN/mm at 1.25mM ATP, respectively. The force generated by smooth and skeletal muscle myosin filaments were increased approximately 54.0% and 100% when ATP concentration increased from 0.5mM to 1.25mM. ATPase activity of smooth and skeletal myosin was significant different (p<0.05), suggesting that higher ATP concentration will be hydrolyzed to enhance the mechanical work during actomyosin interactions.