The Role of the Super-Relaxed State of Myosin in Human Metabolism

Abstract Background The super-relaxed state of myosin (SRX) plays a fundamental role in maintaining the low resting metabolic rate of skeletal muscle. Our previous work on this state has been in animal models. Piperine is a small molecule that has been shown to destabilize the SRX in rabbit fast twitch fibers. Methods Here we extend this work to human muscle obtained from biopsies of the vastus lateralis of both lean and obese subjects. The slow release of nucleotides by myosin in the SRX was measured by incubating permeable fibers in a fluorescent analog of ATP and chasing with ATP. Results The fraction of myosin heads in the SRX was 0.48 ± 0.04 with a lifetime of 148 ± 5 sec in lean subjects and a fraction of 0.41 ± 0.05 and a lifetime of 176 ± 7 sec in obese subjects. Addition of 100 μM piperine decreased the SRX population by 25 ± 4% in lean subjects and 21 ± 4% in obese subjects, with little change in lifetimes. Addition of piperine to human cardiac cells had no effect on the SRX, a requirement for a drug to treat metabolic diseases. Conclusions In human muscle the SRX and its responses to piperine are similar to those seen previously, with no significant differences between muscles from lean and obese subjects. Thus analogs of piperine that have greater specificity could provide effective treatment for metabolic diseases. The SRX provides a potential mechanism contributing to the large dynamic range of metabolic rate.