The cell membrane at first may seem a simple device, but it is in fact a very complex machine. The basic building block is the phospholipid, a set of molecules that have hydrophilic (water loving) heads on one side and a hydrophobic (water hating) tail on the other. Because of this relationship the water loving heads want to be near aqueous environments and the water hating tails like to be near other water hating tails, or fats. Since cells live in aqueous environments, and are filled with aqueous fluids the cell membrane forms two layers with the heads pointing out and the tails pointing towards each other.

This gives rise to many basic properties. Water soluble molecules do not pass easily through this membrane. This also holds the water soluble molecules inside the cell from escaping. In doing so it forms an effective barrier to allow almost total control for the cell to control the balance of many materials between the inside and outside of the cell. This is important for most functions of the cell. Since the cell is in an aqueous environment it mainly only has to worry about controlling the passing of water soluble substances through it’s membrane. Most fat soluble molecules must be chaperoned by carrier proteins through the body since they don’t dissolve well in the aqueous environment, however they easily pass through the cell membrane.

The outer layer of the cell is also coated with groups of sugar molecules of different types that are bound to proteins in the membrane and are called glycoproteins. This serves both for recognition of the cell by other cells and also provides a slight negative charge. Since other cells also have a negative charge, they repel each other so as not to touch.

Understanding these basics of the barrier, let’s move on to carrier proteins. With the barrier stopping most molecules from crossing over into and out of the cell the cell must have some way of allowing molecules to pass. This comes mainly in the form of differing types of carrier membrane proteins. Some are pores that allow molecules of certain types to flow across the membrane at a controlled rate through a process called facilitated diffusion. Others use energy in the form of ATP to move molecules across the membrane through active transport. ATP is produced in the cells by breaking down nutrients from carbohydrates, fats and proteins and storing them as ATP until the cell needs to use it. Another type of transporter called sym-porters, or anti-porters uses gradients that have been set up by active diffusion to move other molecules across the membrane against its concentration gradient.

One great example of active transport is the sodium-potassium ATP pump. It moves 3 sodium molecules out of the cell and 2 potassiums into the cell for every ATP that it uses. By doing this an electro-chemical gradient is set up in the cell. Normally, due to this pump, there is over 10 times the sodium outside the cell as inside and over 200 times the potassium inside as out. This allows both a chemical gradient and an electrical gradient (since most proteins inside the cell have a slight negative charge) that can be used either to drive wanted molecules across the membrane through sym-ports or anti-ports, or to use as a type of rapid signaling by changing the electrical potential across the membrane. Many important molecules like amino acids and glucose are transported this way.

Another important set of membrane proteins act as anchors for the cytoskeleton. The cytoskeleton at the membrane helps control the shape and stability of the cell. Actin molecules form networks of long fibers that are anchored to the membrane by proteins that are supported by other fibers like dystrophin. Dystrophin keeps all of these anchor proteins in a regular pattern that maintains both the structure and stability of the membrane.

The membrane is not static but flows and most of the proteins in it move around. How fluid or static a membrane is can be controlled by what types of molecules are found in the membrane. Cholesterol plays a major role in keeping the membrane from being too fluid. A membrane can contain up to 50% cholesterol. The type of phospholipids contained in the membrane can also play a major role. Phospholipids that are made from saturated fats can lower the fluidity of the membrane where unsaturated will make the membrane more fluid due to a “kink” in their lipid tails. The membrane’s ability to change the composition of its membrane allows the cell to adapt to a wide variety of temperatures and conditions.

In the case of red blood cells, or erythrocytes, the membrane must have several characteristics for the health of the cell. It must be both strong and secure but flexible. Red blood cells need to bend and move to get through the small capillaries, but also need to maintain its disc like structure to have more surface area to allow the exchange of dissolved gasses so necessary to proper function of the body. Without this balance red blood cell membranes can either rupture if they are too liquid or get hung up and form a clot if they are too rigid.

Studies have found that balance of omega-3 fatty acids in the plasma membrane are a good indicator of cardiac health, and even use this balance as a clinical diagnosis tool as a cardiac risk marker. Evidence has shown that long chain polyunsaturated omega-3 fatty acids can reduce the risk of cardio vascular disease. These types of omega acids can be found in both fish and flax seed oil capsules as well as many types of cold water fish and raw foods. The evidence is so strong that the American Heart Association recommends supplementation with fish oil capsules to improve cardiac health.

By giving your body the resources it needs to change the composition of the cell membrane it is able to make a more pliable and adaptable red blood cell membrane. Omega-3 acids have been shown to reduce the risk of primary cardiac arrest, sudden cardiac death, fatal ischemic heart disease, and elicit a protective effect against heart arrhythmias.

References

Medical Physiology, Guyton and Hall

Fundamentals of Bio-Chemistry; Voet, Voet, and Pratt

Incorporation and clearance of Omega-3 fatty acids in erythrocyte Membranes and plasma phospholipids; Cao J, et al.; Clinical chemistry 52:12; 2265-2272; 2006

Harris WS, Von Schacky C. The Omega-3 Index: a new risk factor for death from coronary heart disease?. Prev Med 2004;39:212-220

Siscovick DS, Raghunathan TE, King I. Dietary intake and cell membrane levels of long-chain n-3 polyunsaturated fatty acids and the risk of primary cardiac arrest. JAMA 1995;274:1363-1367

Albert CM, Campos H, Stampfer MJ. Blood levels of long-chain n-3 fatty acids and the risk of sudden death. N Engl J Med 2002;346:1113-1118

Lemaitre RN, King IB, Mozaffarian D, Kuller LH, Tracy RP, Siscovick DS. n-3 Polyunsaturated fatty acids, fatal ischemic heart disease, and nonfatal myocardial infarction in older adults: the Cardiovascular Health Study. Am J Clin Nutr 2003;77:319-325.