Spontaneous pain is ongoing pathological pain that occurs constantly (slow burning pain) or intermittently (sharp shooting pain) without any obvious immediate cause or trigger. The slow burning pain is the cause of much suffering and debilitation. Because the mechanisms underlying this type of slow burning pain are poorly understood, it remains very difficult to treat effectively.

Spontaneous pain of peripheral origin is pathological, and is associated with many types of disease, inflammation or damage of tissues, organs or nerves (neuropathic pain). Examples of neuropathic pain are nerve injury/crush, post-operative pain, and painful diabetic neuropathy.

Previous research has shown that this spontaneous burning pain is caused by continuous activity in small sensory nerve fibres, known as C-fiber nociceptors (pain neurons). Greater activity translates into greater pain, but what causes or limits this activity remained poorly understood.

Now, new research from the University of Bristol, has identified a particular ion channel present exclusively in these C-fiber nociceptors This ion channel, known as TREK2, is present in the membranes of these neurons, and the researchers showed that it provides a natural innate protection against this pain.

Ion channels are specialised proteins that are selectively permeable to particular ions. They form pores through the neuronal membrane. Leak potassium channels are unusual, in that they are open most of the time allowing positive potassium ions (K+) to leak out of the cell. This K+ leakage is the main cause of the negative membrane potentials in all neurons. TREK2 is one of these leak potassium channels. Importantly, the C-nociceptors that express TREK2 have much more negative membrane potentials than those that do not.

Researchers showed that when TREK2 was removed from the proximity of the cell membrane, the potential in those neurons became less negative. In addition, when the neuron was prevented from synthesizing the TREK2, the membrane potential also became less negative.

They also found that spontaneous pain associated with skin inflammation, was increased by reducing the levels of synthesis of TREK2 in these C-fiber neurons.