Calcium Plays a Central Role in the Sensitization of TRPV3 Channel to Repetitive Stimulations

Abstract

Transient receptor potential channels are involved in sensing chemical and physical changes inside and outside of cells. TRPV3 is highly expressed in skin keratinocytes, where it forms a nonselective cation channel activated by hot temperatures in the innocuous and noxious range. The channel has also been implicated in flavor sensation in oral and nasal cavities as well as being a molecular target of some allergens and skin sensitizers. TRPV3 is unique in that its activity is sensitized upon repetitive stimulations. -mediated inhibition and greatly facilitated the activation of TRPV3. We conclude that Ca 2؉ inhibits TRPV3 from both the extracellular and intracellular sides. The inhibition is sequentially reduced, appearing as sensitization to repetitive stimulations. Members of the transient receptor potential (TRP)4 superfamily of cation channels have been recognized to play important roles in sensing various environmental changes inside and outside of cells as well as the whole organisms (1). In mammals, temperature sensing is thought to be accomplished through concerted actions of a minimum of six TRP channels, i.e. TRPA1, -M8, -V4, -V3, -V1, and -V2, each covering a defined temperature range from below 17°C to above 52°C (2, 3). However, the debate remains whether some of these channels, e.g. TRPA1, are really temperature-sensitive (4). In addition, TRPM2, -M4, and -M5 have shown temperature sensing in the presence of second messenger cofactors, such as ADP-ribose and Ca 2ϩ (5, 6). Although some of the thermosensitive TRP channels are clearly expressed and functional in sensory neurons, indicative of their actions in primary afferents, others have been localized in the non-nervous tissues, for example, TRPV3 and -V4 are expressed in skin keratinocytes (7,8) and TRPV3 is, in addition, expressed in the epithelium of tongue and nose (9). The TRPV3 null mice showed some deficits in sensing hot temperatures in the innocuous and noxious range but no other obvious sensory impairment (10). On the other hand, constitutively active mutations of TRPV3 have been linked to hair loss and atopic dermatitis-like skin lesions in rodents (11,12).In addition to temperature, the thermosensitive TRP channels are activated by a large number of structurally unrelated chemical ligands from exogenous as well as endogenous sources (13). This polymodal nature has become a common feature of the TRP channel family, implicating that multiple mechanisms and external stimuli may be involved in the activation and regulation of these channels. TRPV3 was first shown to be activated by 2-aminoethoxydiphenyl borate (2APB), a synthetic compound known to inhibit inositol 1,4,5-trisphosphate receptors and store-operated channels as well as many TRP channels (14, 15). It was soon discovered that a number of natural anti-irritants and flavor enhancers such as camphor, carvacrol, thymol, and eugenol, also use TRPV3 as one of their targets (9, 10). More importantly, cell signaling events leading to the activation of phospholipase C, phosphorylation by...

DrosophilaPainless Is a Ca2+-Requiring Channel Activated by Noxious Heat

“…We did not observe large currents when CaCl 2 was absent in extracellular and intracellular solutions, but larger currents were obtained when physiological intracellular Ca 2ϩ (Ca 2ϩ i ) was present in the pipette solution (Fig. 1 F) (Mohapatra et al, 2003;Strotmann et al, 2003;Chuang et al, 2004;Nagata et al, 2005;Talavera et al, 2005;Nilius et al, 2006;Tong et al, 2006;Doerner et al, 2007;Zurborg et al, 2007;Xiao et al, 2008 i , heat-evoked currents were almost negligible (Ͻ50 pA at Ϫ60 mV) (Fig. 2 A).…”

Two amino acid residues determine 2-APB sensitivity of the ion channels TRPV3 and TRPV4

“…This phenomenon is in contrast to wild-type TRPV3, which sensitizes in response to repetitive/continuous stimulation of chemicals or heat (14,16). The mechanism underlying TRPV3 sensitization is proposed to be a loss of calcium inhibition of this channel (22). Because desensitization of most other TRP channels (such as TRPV1 and TRPA1) to chemical or temperature stimuli also depends on extracelullar calcium (24,25), we set out to test whether extracellular calcium has a role in 2-APB-evoked desensitizing responses in TRVP3-R696K.…”

“…In the absence of chemical stimulators (for example camphor or 2-APB), voltage steps from Ϫ120 to ϩ180 mV (20 mV step) did not activate currents in HEK293 cells transfected with wild-type TRPV3, indicating that TRPV3 (unlike TRPV1 and TRPM8) is not activated by voltage alone at the range tested here (20,22). However, in the presence of 30 M 2-APB, a voltage-dependent current was activated (Fig.…”

“…Surprisingly, we found out that TRPV3-R696K responded relatively normally to 2-APB in the absence of extracellular calcium. Also, ablating a putative calcium-binding site at the TRPV3 pore, which has been shown to mediate calcium-inhibition, appears to override the 2-APB deficiency of TRPV3-R696K (22). However, because we record wildtype-like camphor responses and observe normal voltage modulation of TRPV3-R696K, it is unlikely that this mutation is causing an overall change in gating efficiency or a general effect of extracellular calcium.…”

“…A putative Ca 2ϩ -binding residue in the pore loop domain, aspartate 641, is conserved among all TRPV channels, and is critical to permeation properties of TRP channels (26,27). Mutation of D641 into asparagine (N) has been shown to reduce ruthenium red block and high affinity extracelullar calcium inhibition of TRPV3 and other TRP channels (17,22,26,27). Therefore, we examined whether the D641N mutation could relieve the TRPV3-R696K clone from calcium-dependent loss of 2-APB response.…”