 The Role of Calcium in Heat Perception
Calcium: Does a Body PainCalcium ions play a major role in the perception of noxious heat caused by the capsaicin in hot peppers. There naturally occurs outside the neuron a greater amount of calcium ions (about 10,000 times greater) than inside the cell. When those ions are allowed to cross the cell membrane, neurotransmitters are released, stimulating action potential. Two proteins that are part of the cell membrane maintain this gradient of ions. The first is a sodium/calcium ion protein, which releases calcium ions within the cell, in exchange for sodium ions from outside the cell. The second protein is a calcium ion pump that forces the calcium ions out of the cell. Both systems are dependent upon the use of ATP, a cell's energy. Specifically, the ion channel that capsaicin binds to is called the vanilloid receptor, named after a portion of the capsaicin molecule. When capsaicin attaches to these receptors, they are forced open, allowing calcium ions to enter the cell. The receptors stay open as long as the capsaicin molecules are bound. A large amount of calcium within the cell is dangerous, because it disrupts the electrochemical balance within the neuron. When calcium ions stimulate neurotransmitter release, a response is generated. This is a normal process in the nervous system. But when too much calcium is present, cell death occurs. Although the specific cause of death is unknown, it is assumed that the ions somehow disrupt the normal cellular processes that enable it to survive. The assumed reason that we perceive peppers as spicy is that the influx of calcium ions into the neuron causes a certain degree of cell death, and ultimately, numbing pain. Interestingly, the pain caused by capsaicin can be relieved by eating or drinking milk products such as milk, cheese, sour cream or yogurt. These products all contain casein, an enzyme that breaks the weak interactions between capsaicin molecules and pain receptors.
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