No doubt, every year on February 7 we celebrate the famous Rose Day, the first day of the Valentine’s Week, when people send roses to their loved ones to express their unconditional love.
You know, looking at the price of roses, it seems to me that February is the month when we love (our loved ones) the most. More than any other month of the year… But let’s get back to our roses.
Roses are amazingly beautiful flowers with a very rich scent. Whenever we see roses, we feel an urge to smell them. The scent of roses is extremely complex and is made up of hundreds of volatile molecules. But it’s not a problem for us – it is estimated that the human nose can detect up to 1 trillion different scents.
Different odors are recognized by distinct olfactory receptors (G protein-coupled receptors) on the cell membranes of olfactory sensory neurons. These receptors trigger cyclic nucleotide-gated (CNG) ion channels leading to sodium and calcium influxes and then to depolarization and excitation of the olfactory sensory neurons. The exited neurons then fire action potentials to the brain, informing us about the odor.
Unfortunately, not all of us can enjoy the enchanting scent of roses. Millions of people worldwide suffer from various olfactory disorders, including anosmia, a complete loss of smell.
In 2011, Frank Zufall Group showed that people with congenital insensitivity to pain, caused by loss-of-function mutations in sodium channel Nav1.7 (SCN9), are unable to sense any of the odors. They demonstrated that the presence of Nav1.7 in axons of olfactory sensory neurons is essential to initiate information transfer from these neurons to the projection neurons in the olfactory bulb (see here).
To put it simply, the olfactory receptors of these people detect odors, and the olfactory sensory neurons get excited. The only problem is that they cannot transmit this excitation to the brain. And this is because of one tiny but very mighty ion channel. Nav1.7.