Carbon Monoxide: A Deadly Poison and a Neurotransmitter
A Potentially Deadly Poison
Carbon monoxide in the environment is a deadly poison that kills hundreds of people in North America every year. Unlike some poisonous gases, it's produced by devices that we have in our homes as well as by industrial processes. It's a colorless, odorless, and tasteless gas and an insidious poison. We may not realize that we are being poisoned by carbon monoxide, since one of its effects is to make us confused and sleepy.
Strangely, this very toxic gas is a normal component of our bodies, where it's present in tiny quantities. It plays an important role in our nervous system and acts as a signaling molecule. Signaling molecules carry messages within or between cells or from one part of the body to another. A signaling molecule works by triggering a specific effect when it reaches its new location.
The chemical formula for carbon monoxide is CO. It's a simple molecule that is made of one carbon atom and one oxygen atom. This simple molecule can have big effects, however, depending on its concentration.
Carbon monoxide is produced by the incomplete combustion of a fuel. Any device that burns gas, oil, kerosene, coal, charcoal, or wood can produce the gas.
Sources of Carbon Monoxide
Devices that may release CO in and around a home include furnaces, water heaters, gas stoves, propane space heaters, portable generators, charcoal grills, car engines, and fireplaces. Gasoline-powered lawn mowers, leaf-blowers, weed trimmers, chain saws, and snow blowers are also potential sources of CO.
Unfortunately, every year some people who have tried to keep warm in winter have died of carbon monoxide poisoning. Space heaters and stoves are frequently responsible for these deaths, which usually occur during power failures. Propane space heaters should never be used indoors and a gas stove should never be left on to warm a home.
It's a good idea to plan how to keep warm before a potential power failure occurs. If you have elderly acquaintances with problems that may affect their safety, you might want to help them prepare for a power failure. It would also be a good idea to visit them when there is no power to see how they're doing. Elderly people and babies are much more susceptible to health problems in cold temperatures than people of other ages.
Why Is Inhaled CO Dangerous?
Our red blood cells contain a protein called hemoglobin. Hemoglobin's function is to transport oxygen from the lungs to the body's tissue cells, which use the oxygen to produce energy.
Carbon monoxide joins to hemoglobin, producing a substance known as carboxyhemoglobin. Carboxyhemoglobin can't carry as much oxygen as normal hemoglobin. The carbon monoxide also causes the hemoglobin to hold on to the oxygen molecules that have managed to join to it very tightly, preventing them from being released to the cells.
Researchers think that inhaled carbon monoxide hurts us in other ways besides blocking a cell's oxygen supply. It joins to myoglobin, a protein in muscle. This may cause muscle weakness. Carbon monoxide may also affect the functioning of the mitochondria, the structures in cells that produce the energy which we need.
According to the CDC (Centers for Disease Control and Prevention), in the United States between 400 and 500 people die from CO poisoning every year. In addition, more than 20,000 people need to visit the emergency department of a hospital due to CO exposure and more than 4,000 people need to be hospitalized.
Possible Symptoms of Carbon Monoxide Poisoning
The symptoms of carbon monoxide poisoning may at first mimic the effects of the flu or other disorders. If an affected person stays in the dangerous environment they may become confused and fatigued. At this stage it may be hard for someone to voluntarily evacuate from the dangerous area. CO is especially dangerous for people who are already asleep.
The most common symptoms of carbon monoxide poisoning are as follows:
- chest pain
- shortness of breath
These symptoms can be caused by other health problems, too, but they may indicate the present of carbon monoxide in the air. A doctor must be consulted if the symptoms appear. CO exposure and many other conditions that include several or the most serious of the symptoms listed above are medical emergencies.
A person who is or may be suffering from carbon monoxide poisoning needs to be removed to an atmosphere with fresh air. The rescuer should quickly open doors and windows before they help someone. This is important for both the victim and the safety of the rescuer. The patient may need to receive supplemental oxygen. Even if the patient apparently recovers, they should be taken to a hospital.
Preventing CO Poisoning
Carbon monoxide poisoning may have devastating consequences, but it can be prevented. The most important precautionary steps are to use equipment in safe conditions and to have working carbon monoxide detectors in the home. Here are some safety tips.
- Place a CO detector on every floor of your home, especially near sleeping areas.
- Make sure that detectors that are connected to an electrical outlet have a battery backup.
- Replace the batteries in detectors regularly on easily remembered dates, such as family birthdays or the days when clock times change.
- Get equipment such as furnaces and water heaters serviced once a year.
- Make sure that devices such as stoves and fireplaces are vented.
- Get chimneys cleaned regularly.
- Don't leave a car running in a garage, even when the garage door is open.
- Don't turn on gas-powered equipment such as chain saws in enclosed spaces.
- Don't turn on generators in or near a home.
- Never use a propane or kerosene space heater or a charcoal grill indoors.
It's important to have a CO detector in enclosed areas of leisure boats. In a recent incident in British Columbia, two children sleeping in a cabin were affected by the gas but luckily recovered. According to an RCMP press release about the incident, it's important that carbon monoxide poisoning isn't mistaken for seasickness, intoxication, or heat stress.
A Carbon Monoxide Detector Poll
Do you have carbon monoxide detectors in your home?
Carbon Monoxide as a Neurotransmitter
Carbon monoxide and two other dangerous environmental gases—nitric oxide and hydrogen sulfide—are present in our bodies in very small quantities. These gases appear to play a vital role in a wide range of body processes.
One process involving CO is the transfer of nerve impulses from one neuron, or nerve cell, to another. This transfer is called neurotransmission and is carried out by chemicals known as neurotransmitters. Carbon monoxide, nitric oxide, and hydrogen sulfide are all neurotransmitters. They behave a little differently from other chemicals in the category, however.
Most neurotransmitters are stored in sacs called vesicles at the end of a neuron. The vesicles release the chemicals when a nerve impulse arrives. The molecules travel across the gap that is present between neurons and bind to receptors on the membrane of a second neuron. Once this union takes place, a new nerve impulse is generated in the second neuron. Some neurotransmitters have the opposite effect and stop a new nerve impulse from being generated, however.
Carbon monoxide and the other gaseous neurotransmitters aren't stored in vesicles but are rapidly made when they're needed. In addition, they don't bind to receptors on the second neuron but move into the neuron. Like other neurotransmitters, they regulate the passage of the nerve impulse. They may actually act as neuromodulators, at least in some parts of the body. Neuromodulators influence the action of neurotransmitters instead of being neurotransmitters themselves.
Other Functions of CO
Researchers have discovered some specific functions of carbon monoxide in the body.
- It relaxes the muscles in the blood vessels, causing the vessels to widen and blood pressure to decrease.
- In rats, it protects against cardiac ischemia (a restriction in blood flow to the heart).
- It causes relaxation of the muscles responsible for gut contraction.
- In lab experiments with animals it reduces inflammation.
- In the brain, carbon monoxide modulates the release of other neurotransmitters.
Carbon monoxide, nitric oxide, and hydrogen sulfide are sometimes called gasotransmitters instead of neurotransmitters. They seem to have similar functions in the body, but they sometimes work in different ways from each other.
Gasotransmitters in the Future
Scientists suspect that gasotransmitters could be used as medications if we understood their behavior better. In 2011 an organization called the European Network on Gasotransmitters, or ENOG, was created. The network holds conferences, meetings, and workshops. Its aim is to discover the functions and methods of action of the different gasotransmitters and to develop their use as medications. The network also wants to discover the differences and similarities in the actions of carbon monoxide, nitric oxide, and hydrogen sulfide.
It's interesting to realize that a potentially deadly gas such as carbon monoxide could have important health benefits. There is so much that we still need to learn about the human body. Understanding more about the action of carbon monoxide and the other gasotransmitters could lead to significant medical advances.
References and Resources
Facts about carbon monoxide poisoning from the CDC
Information about carbon monoxide dangers and safety from the Government of Canada
CO safety tips from the City of Calgary
Children affected by carbon monoxide while boating from the CBC (Canadian Broadcasting Corporation)
Tinajero-Trejo M, Jesse HE, Poole RK. Gasotransmitters, poisons, and antimicrobials: it’s a gas, gas, gas! F1000Prime Reports. 2013;5:28. doi:10.12703/P5-28.
News and information from the European Network on Gasotransmitters
Questions & Answers
© 2013 Linda Crampton