Skeletal Muscle Hypertrophy Through Mechanoreceptors

    I am a big fan of body building as it is a fun way for me to stay physically active and feel good about myself. In class, we have just recently gone over how muscle contractions work through the shortening of the sarcomere and I started to wonder how muscles hypertrophy occur at that intracellular level through resistance training. Of course, we learned that cell signaling through the growth hormone can lead to cells undergoing mitosis more often, increasing the size of the muscle, but how does a physical action lead to cell growth? By doing some research on PubMed, I found the answer to that question, and it was an answer that I already kind of knew. Near the very beginning of the semester, we got introduced to three different kinds of channels, a voltage gated channel, a ligand gated channel, and a mechanosensory gated channel. That last channel’s classification was the answer to the conversion of physical action to chemical action!

    Muscle hypertrophy using resistance training occurs through mechanoreceptors that when stimulated and stretched, start a cascade of cellular pathways leading to more myofibril synthesis. A lot of the articles that I found were very complex and had gone in-depth into those cellular pathway cascades, but here I will try to summarize one of them into a more digestible and simple idea. According to this article, one way for muscle hypertrophy to occur through resistance training is with the help of sarcolemnic mechanically activated channels that let Ca2+ enter the muscle fiber. These channels can open in a variety of ways but there are three proposed in the article. All three open the channels through tensioning the sarcolemma but hypothesize that each is done differently, either through simple tensioning of the sarcolemma during contraction and relaxation, through tensioning the tethering of the channel itself directly, or tensioning the tether of a nearby protein that indirectly opens the channel. Once the channel is opened, Ca2+ ions can rush in and bind to certain proteins that start the cascade of myofibril synthesis leading to muscle hypertrophy. This contraction mechanism is also very cool as it is a “self-regulating” cycle since it uses Ca2+ for two different purposes. Every time we contract, Ca2+ is released to unbind tropomyosin, but that Ca2+ is also used as a transcription factor that starts more myofibril synthesis to replace worn down myofibrils!

Reference:
Mirzoev T. M. (2023). Mechanotransduction for Muscle Protein Synthesis via Mechanically Activated Ion Channels. Life (Basel, Switzerland), 13(2), 341. https://doi.org/10.3390/life13020341