Acid sensing ion channels
After tissue damage, there is accumulation of hydrogen ions. These protons may activate nociceptors via acid sensing ion channels - a family of sodium channels on cell membranes that have a role in pain transmission.
Of special interest is one type found only in small dorsal root ganglion neurons that are responsible for activation of nociceptors.
Reference: Suzuki R, Sikandar S, Dickenson AH. Nociception: basic principles. In: Bruera ED, Portenoy RK (eds) Cancer Pain Assessment and Management. Cambridge University Press . Cambridge 2010, P 6.