Activated by Force

Science Signaling  13 Sep 2011:
Vol. 4, Issue 190, pp. ec255
DOI: 10.1126/scisignal.4190ec255

Organisms must distinguish between gentle, innocuous touches and intense applications of force that could cause injury in order to respond appropriately. Controversy exists over whether cationic channels of the TRP (transient receptor potential) family, sodium channels of the DEG/ENaC (degenerin and epithelial sodium channel) family, or both are the mechanoelectrical transduction channels in nociceptor neurons that transduce intense mechanical stimuli into electrical signals. In the nematode Caenorhabditis elegans, ASH neurons are nociceptors that respond to multiple stimuli, including mechanical force, and contain the DEG/ENaC channels DEG-1 and UNC-8 and the TRPV channels OSM-9 and OCR-2. Geffeney et al. performed in vivo electrophysiological recordings of ASH neurons in C. elegans, which they activated by applying pressure to the nose area. The major mechanoreceptor currents elicited were rapidly activated, decayed during the course of mechanical stimulation, and varied in amplitude according to the force applied. DEG/ENaC channels mediated the mechanoreceptor currents, as indicated by the sensitivity of these mechanoreceptors to amiloride and lack of extracellular Na+ ions. Genetic analyses revealed that DEG-1 was required to generate mechanoreceptor currents and was the major pore-forming subunit of the mechanoelectrical transduction channel, and that deletion of unc-8, osm-9, or ocr-2 did not affect the mechanoreceptor current. Thus, DEG-1 is the key mechanoelectrical transduction channel in ASH neurons in C. elegans, and the authors suggest that the TRPV channels may not be involved in detecting intense mechanical stimuli but rather play a role in encoding and transmitting the associated sensory information (see also the Commentary by Nelson et al.).

S. L. Geffeney, J. G. Cueva, D. A. Glauser, J. C. Doll, T. H.-C. Lee, M. Montoya, S. Karania, A. M. Garakani, B. L. Pruitt, M. B. Goodman, DEG/ENaC but not TRP channels are the major mechanoelectrical transduction channels in a C. elegans nociceptor. Neuron 71, 845–857 (2011). [PubMed]

A. M. Nelson, K. L. Marshall, E. A. Lumpkin, DEG/ENaCs lead by a nose: Mechanotransduction in a polymodal sensory neuron. Neuron 71, 763–765 (2011). [PubMed]