The mammalian sensory system is capable of discriminating thermal stimuli ranging from noxious cold to noxious heat. Principal temperature sensors belong to the TRP cation channel family, but the mechanisms underlying the marked temperature sensitivity of opening and closing ('gating') of these channels are unknown. Here we show that temperature sensing is tightly linked to voltage-dependent gating in the cold-sensitive channel TRPM8 and the heat-sensitive channel TRPV1. Both channels are activated upon depolarization, and changes in temperature result in graded shifts of their voltage-dependent activation curves. The chemical agonists menthol (TRPM8) and capsaicin (TRPV1) function as gating modifiers, shifting activation curves towards physiological membrane potentials. Kinetic analysis of gating at different temperatures indicates that temperature sensitivity in TRPM8 and TRPV1 arises from a tenfold difference in the activation energies associated with voltage-dependent opening and closing. Our results suggest a simple unifying principle that explains both cold and heat sensitivity in TRP channels.Mammals sense ambient temperature through primary afferent sensory neurons of the dorsal root and trigeminal ganglia 1,2 . These cells convey thermal information from peripheral tissues to the spinal cord and brain, where the signals are integrated and interpreted, resulting in appropriate reflexive and cognitive responses. The mammalian sensory system is capable of detecting and discriminating thermal stimuli over a broad temperature spectrum, ranging from noxious cold (,8 8C) to noxious heat (.52 8C), which implies the existence of different types of temperature sensors with distinct thermal sensitivities 2 . Accumulated evidence suggests that the principal temperature sensors in the sensory nerve endings of mammals belong to the transient receptor potential (TRP) superfamily of cation channels 3,4 . At present, six temperature-sensitive TRP channels (or thermoTRPs) 2 have been described, that together cover almost the entire range of temperatures that mammals are able to sense. Four TRP channels belonging to the TRPV subfamily are activated by heating, with characteristic activation temperatures ranging from warm temperatures (.25 8C for TRPV4; .31 8C for TRPV3) 5-9 to heat (.43 8C for TRPV1) 10 and noxious heat (.52 8C for TRPV2) 11 . TRPM8 and TRPA1 (ANKTM1) are activated by cooling, (,28 8C for TRPM8; ,18 8C for TRPA1) [12][13][14] ; although the cold-sensitivity of TRPA1 has been disputed 15 . The origin of the remarkably steep temperature sensitivity of the thermoTRPs is still obscure. Until now, three possible mechanisms for temperature-dependent channel gating have been envisaged 3 . Changes in temperature could lead to the production and binding of channel-activating ligands. Alternatively, the channel protein may undergo temperature-dependent structural rearrangements leading to channel opening. Finally, thermoTRPs may be able to sense changes in membrane tension due to temperature-dependent lipid bilayer...

TRPV4 is a widely expressed cation channel of the 'transient receptor potential' (TRP) family that is related to the vanilloid receptor VR1 (TRPV1). It functions as a Ca2+ entry channel and displays remarkable gating promiscuity by responding to both physical stimuli (cell swelling, innoxious heat) and the synthetic ligand 4alphaPDD. An endogenous ligand for this channel has not yet been identified. Here we show that the endocannabinoid anandamide and its metabolite arachidonic acid activate TRPV4 in an indirect way involving the cytochrome P450 epoxygenase-dependent formation of epoxyeicosatrienoic acids. Application of 5',6'-epoxyeicosatrienoic acid at submicromolar concentrations activates TRPV4 in a membrane-delimited manner and causes Ca2+ influx through TRPV4-like channels in vascular endothelial cells. Activation of TRPV4 in vascular endothelial cells might therefore contribute to the relaxant effects of endocannabinoids and their P450 epoxygenase-dependent metabolites on vascular tone.

Mg2؉ is an essential ion involved in a multitude of physiological and biochemical processes and a major constituent of bone tissue. Recently, a positional candidate screening approach in consanguineous families with hypomagnesemia with secondary hypocalcemia (HSH) revealed a critical region identified on chromosome 9q21.13 (2, 3). Individuals suffering from HSH display neurologic symptoms including seizures and tetany during infancy. These symptoms can be suppressed by life-long dietary magnesium supplementation, but, untreated, the disease may be fatal or result in neurological damage. The pathophysiology of HSH is largely unknown, but physiological studies have shown that there are defects in both intestinal Mg 2ϩ absorption and renal Mg 2ϩ reabsorption. Subsequent analysis of the critical region pointed to a gene, TRPM6, which was mutated in patients with HSH (2, 3). The TRPM6 protein is a member of the transient receptor potential channel (TRP) family (4).Based on the structural and sequence similarities between individual TRP proteins, three subgroups are distinguished, namely the canonical TRPC-, the vanilloid-like TRPV-, and the melastatin-like TRPM subfamilies. Most members of the TRPC-and TRPV-subfamilies have been characterized as Ca 2ϩ -permeable cation channels playing a role in Ca 2ϩ homeostasis and signaling (4). However, the functional characterization of TRPM proteins is much more incomplete. TRPM6 shows 50% sequence homology with TRPM7 (also known as TRP-PLIK), which forms a Ca 2ϩ and Mg 2ϩ -permeable cation channel. Unlike other members of the TRP family, TRPM6 and TRPM7 contain long carboxyl-terminal domains with similarity to the ␣-kinases (5). The identification of TRPM6 as the gene mutated in HSH represents the first case in which a human disorder has been attributed to a channel kinase.The aim of the present study was to functionally characterize TRPM6 as the first molecularly identified protein involved in active Mg 2ϩ (re)absorption. To this end, the (sub)localization of TRPM6 was investigated by immunohistochemical analysis of kidney and duodenum sections. Subsequently, human TRPM6 cDNA was cloned, transfected into human embryonic kidney

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We have studied activation by phorbol derivatives of TRPV4 channels, the human VRL-2, and murine TRP12 channels, which are highly homologous to the human VR-OAC, and the human and murine OTRPC4 channel. ] i inhibits the channel with an IC 50 of 406 nM. Ruthenium Red at a concentration of 1 M completely blocks inward currents at ؊80 mV but has a smaller effect on outward currents likely indicating a voltage dependent channel block. We concluded that the phorbol derivatives activate TRPV4 (VR-OAC, VRL-2, OTRPC4, TRP12) independently from protein kinase C, in a manner consistent with direct agonist gating of the channel.