The heart is important because it’s a symbol of love, of course. But it’s also a veritable engine for each of our bodies, continually pumping to keep us moving. Because it has such a big presence in our culture—and in our lives—it’s good to know exactly what your engine is made of and how it operates. As with all our organs, DNA plays a big role, and the heart owes some of its function to a gene known as MYH6.
It’s estimated that the average person has 37.2 trillion cells in their body, and each one of them needs access to oxygen, nutrients, and a waste disposal mechanism. Fortunately, evolution has equipped us with an efficient, multipurpose network for handling these needs called the cardiovascular system. This system is comprised of blood vessels that extend to all parts of the body and connect back to the heart. Among its many functions, the cardiovascular system takes oxygen from the lungs, nutrients from the intestines, and hormones from the brain or kidneys and distributes them throughout the body. Cells also produce waste, which can be toxic if it builds up. Your cardiovascular system prevents this from happening though by sweeping those waste products away from cells and taking them to the kidney or liver where they’re eliminated. For all of this to happen, though, you need a heart.
A person’s heart beats in a coordinated rhythm that allows unidirectional and consistent blood flow. This coordination is achieved through electrical pulses that start in specialized cells (known as pacemaker cells) in the upper part of the heart. These cells are unlike any other cell in the body because they can generate an electrical pulse on their own, independent of nerve cells.
The electrical pulse shoots through the heart like a wave, causing muscle contractions at the leading edge of the pulse. Electricity causes calcium to flood into the muscle cells, which causes the actin proteins to become open and unprotected—at which point myosin (like αMHC) can bind and cause contraction3.
Your heart is a big muscle that functions like a fancy turkey baster: Muscles squeeze, which forces the blood inside the heart to shoot out of it and into blood vessels. While the principle behind this analogy fits, the biology is a little more complex. In general, the heart separates blood into two categories: blood being sent to the lungs, and blood being sent everywhere else. This is an important distinction to make because your heart has developed to keep the these categories separated from one another. Four different pockets (known as chambers) allow the heart to segregate blood based on where it’s been, and where it’s going. The interconnected nature of these chambers helps blood flow smoothly through the heart, but it wouldn’t flow correctly if the heart squeezed all of the chambers at the same time. To keep things organized, the heart squeezes each chamber in a particular order which forces blood to move in the proper direction. One complete contraction of the heart is called a beat, and the average adult human heart will beat 60 to 100 times every minute.
The ability to generate a powerful contraction is vital to this process and your body relies on some of the same machinery used in other muscles to generate force. Muscles use proteins known as myosin and actin—along with a highly energetic molecule known as ATP—to generate power1. Together, myosin and actin allow your muscles to extend and contract with force.
Imagine that you are standing next to a balloon filled with helium. Picture the balloon resting against the ceiling—in order to bring the balloon closer, you reach out, grab the string, and pull it down. Although the balloon is light, you still have to use some energy to grab it and pull it down. When you let go, it releases and moves back to the ceiling. This is the basic concept behind muscle contraction. Myosin proteins reach out and grab onto actin filaments. Using ATP, they’re able to pull those filaments in a single direction, which causes muscle contraction. Release of the actin leads to a release of the muscle tension and allows muscle extension.
The heart functions in this same way, and relies on special myosin proteins—including one known as alpha Myosin Heavy Chain (αMHC), which is coded in the DNA by the MYH6 gene1. αMHC is produced from very early on in embryonic development and is required for heart formation. Changes in the MYH6 gene are believed to affect heart contractions because they might alter myosin’s ability to pull actin, and therefore affect the heart’s ability to forcefully contract1,2. In line with this, variants in the MYH6 gene have been correlated with subtle changes in a person’s heart rate2. This is a good example of how changes to even a single gene could potentially affect our physical being.
1England, Jennifer, and Siobhan Loughna. “Heavy and Light Roles: Myosin in the Morphogenesis of the Heart.” Cellular and Molecular Life Sciences 70.7 (2013): 1221–1239. PMC. Web. 14 Feb. 2018.
2Den Hoed, Marcel et al. “Identification of Heart Rate–associated Loci and Their Effects on Cardiac Conduction and Rhythm Disorders.” Nature genetics 45.6 (2013): 621–631. PMC. Web. 12 Feb. 2018.
3Pfeiffer, Emily R. et al. “Biomechanics of Cardiac Electromechanical Coupling and Mechanoelectric Feedback.” Journal of Biomechanical Engineering 136.2 (2014): 0210071–02100711. PMC. Web. 14 Feb. 2018.