TRPV channels as temperature sensors.

The past year has seen a doubling in the number of heat-sensitive ion channels to six, and four of these channels are from the TRPV family. These channels characteristically have Q(10) values of >10 above the thermal threshold, very different from the Q(10) values of 1.5-2.0 seen in most ion channels. Cells expressing TRPV1 show similar temperature sensitivity to small capsaicin-sensitive nociceptor neurons, consistent with these neurons expressing homomers of TRPV1. A-delta fibres exhibit properties that may be explained by TRPV2 containing channels which is present in large diameter sensory neurons that do not express TRPV1. TRPV3 has a lower temperature threshold and may contribute to warm-sensitive channels together with TRPV1. Warm sensation may also be transduced by TRPV4 expressing sensory neurons and hypothalamic neurons. We can now look forward to further work defining the properties of the recombinant channels in more detail and a re-analysis of endogenous i(heat) currents in thermosensitive neurons and other cells. Data from the study of mice in which TRPV2, TRPV3 or TRPV4 have been deleted are also eagerly awaited.