Surrounding each cell is a lipid bilayer, also known as the plasma membrane. Although essential oil constituents can readily pass through this membrane (see "Bioactivity of Essential Oils"), they can also directly influence specialized membrane proteins called ion channels. Ion channels control the influx and outflux of ions through the membrane. Ions are molecules with a net positive or negative electrical charge, such as Na+ (sodium ion) or Cl– (chloride ion). This influx and outflux of ions in cells is responsible for nerve impulse and muscle contraction, among many other functions.
In human cells there are several different types of ion channels. Essential oil constituents have been shown to interact with several of these. The main chemical constituent of Peppermint oil, menthol, is very active in interacting with ion channels.
Sodium channels are voltage-gated, which means that they open when there is a great enough disparity in electrical charge on either side of the membrane. When this occurs, sodium ions (Na+) flood into the cell. These channels are crucial for stimulating neurons and muscle fibers.
Menthol’s soothing properties are associated with its ability to support the healthy functioning of these neuronal sodium channels.* In fact, menthol is rapidly concentrated in the brain when administered systemically, implying that it can exert its effects directly on the central nervous system.*
Another type of voltage-gated channels are calcium channels. Like sodium channels, when there is an electrical charge disparity, calcium ions (Ca2+) flood into the cell. This calcium ion influx is crucial for many physiological functions in neurons, and for contracting all types of muscle cells (skeletal, cardiac, and smooth).
Menthol can help to relax smooth muscle tissue, including the smooth muscle that lines the colon.* This relaxant property is due to menthol’s ability to help keep calcium channels working optimally.* Relaxing colon smooth muscle reduces the movement of the bowels, easing occasional bowel looseness.*
Transient Receptor Potential Channels (TRP)
TRP channels serve as sensors to such physical stimuli as temperature, pressure, and stretch. When activated, they cause an influx of positively charged ions. When you swallow Peppermint oil, oftentimes you feel a cooling sensation. This is because menthol activates the TRPM8 receptor, which is an indicator of cold.* In fact, menthol and cold use the exact same mechanism to activate the TRPM8 sensor.*
Gamma-Aminobutyric Acid (GABA) Receptors
GABA is a neurotransmitter whose receptor is a chloride ion (Cl–) channel. Neurotransmitters are the brain’s chemical messengers. Menthol helps support the normal functioning of GABA receptors.* This invigorating effect is well known to Peppermint users.*
Many of the benefits of Peppermint oil can be explained by menthol’s interactions with ion channels.* Taken together, there is no question that Peppermint oil is a versatile essential oil with many benefits. Plus, it smells and tastes great!