Vertebrate and invertebrate TRPV-like mechanoreceptors

Our senses of touch, hearing, and balance are mediated by mechanosensitive ion channels. In vertebrates, little is known about the molecular composition of these mechanoreceptors, an example of which is the transduction channel of the inner ear's receptor cells, hair cells. Members of the TRP family of ion channels are considered candidates for the vertebrate hair cell's mechanosensitive transduction channel and here we review the evidence for this candidacy. We start by examining the results of genetic screens in invertebrates that identified members of the TRP gene family as core components of mechanoreceptors. In particular, we discuss the Caenorhabditis elegans OSM-9 channel, an invertebrate TRPV channel, and the Drosophila melanogaster TRP channel NOMPC. We then evaluate basic features of TRPV4, a vertebrate member of the TRPV subfamily, which is gated by a variety of physical and chemical stimuli including temperature, osmotic pressure, and ligands. Finally, we compare the characteristics of all discussed mechanoreceptive TRP channels with the biophysical characteristics of hair cell mechanotransduction, speculating about the possible make-up of the elusive inner ear mechanoreceptor.