Voltage is a partial activator of rat thermosensitive TRP channels

105

Temperature-activated transient receptor potential ion channels (thermoTRPs) are polymodal detectors of various stimuli including temperature, voltage, and chemicals. To date, it is not known how TRP channels integrate the action of such disparate stimuli. Identifying specific residues required for channel-activation by distinct stimuli is necessary for understanding overall TRP channel function. TRPV3 is activated by warm temperatures and various chemicals, and is modulated by voltage. One potent activator of TRPV3 is 2-aminoethyl diphenylborinate (2-APB), a synthetic chemical that modulates many TRP channels. In a high-throughput mutagenesis screen of Ϸ14,000 mutated mouse TRPV3 clones, we found 2 residues (H426 and R696) specifically required for sensitivity of TRPV3 to 2-APB, but not to camphor or voltage. The cytoplasmic N-terminal mutation H426N in human, dog, and frog TRPV3 also effectively abolished 2-APB activation without affecting camphor responses. Interestingly, chicken TRPV3 is weakly sensitive to 2-APB, and the equivalent residue at 426 is an asparagine (N). Mutating this residue to histidine induced 2-APB sensitivity of chicken TRPV3 to levels comparable for other TRPV3 orthologs. The cytoplasmic C-terminal mutation R696K in the TRP box displayed 2-APB specific deficits only in the presence of extracellular calcium, suggesting involvement in gating. TRPV4, a related thermoTRP, is 2-APB insensitive and has variant sequences at both residues identified here. Remarkably, mutating these 2 residues in TRPV4 to TRPV3 sequences (N426H and W737R) was sufficient to induce TRPV3-like 2-APB sensitivity. Therefore, 2-APB activation of TRPV3 is separable from other activation mechanisms, and depends on 2 cytoplasmic residues.A subset of transient receptor potential (TRP) ion channels have important roles in sensory biology, including pain and thermosensation (1-4). The requirement of several so-called thermoTRPs in thermosensation in vivo has been demonstrated, suggesting that these ion channels have a physiological role as molecular thermometers (5-9). Thresholds of temperatureactivation of thermoTRPs are shifted in the presence of chemical agonists, effectively modulating thermosensation (1, 10-12). Several natural and synthetic compounds have been identified as agonists or antagonists for each of the thermoTRPs (13). However, little is known about how these chemicals modulate TRP channel activity.TRPV3, one of these thermoTRPs, is a nonselective cation channel expressed primarily in mammalian keratinocytes, and is involved in thermosensation (4,7,14). Like other thermoTRP channels, TRPV3 is a polymodal detector of temperature (heat) and chemicals. TRPV3 agonists include structurally-related natural compounds such as camphor, thymol, and carvacrol (15, 16). One of the most potent TRPV3 agonists is 2-aminoethyl diphenylborinate (2-APB), a synthetic compound that modulates the activity of many ion channels. It is a common activator of the heat-gated TRPV ion-channels TRPV1, TRPV2, and TRPV3 (17,18). Besides i...

Section: Voltage-dependent Response Remained Intact In 2-apb Mutantsmentioning

confidence: 96%

mentioning

confidence: 99%

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

Grandl

Bandell

et al. 2009

105

“…Such dynamic permeability change could not have happened before agonist application, that is, for hydrophilic cap-ET at starting time points of our YO-PRO-1 transport experiments. It is more likely that initial cap-ET entry was due to a sufficient basal channel activity of TRPV1 at room temperature (43)(44)(45).…”

Section: Discussionmentioning

confidence: 99%

Activity-dependent targeting of TRPV1 with a pore-permeating capsaicin analog

Wang

Chuang³

et al. 2011

The capsaicin receptor TRPV1 is the principal transduction channel for nociception. Excessive TRPV1 activation causes pathological pain. Ideal pain mangement requires selective inhibition of hyperactive pain-sensing neurons, but sparing normal nociception. We sought to determine whether it is possible to use activity-dependent TRPV1 agonists to identify nerves with excessive TRPV1 activity, as well as exploit the TRPV1 pore to deliver charged anesthetics for neuronal silencing. We synthesized a series of permanently charged capsaicinoids and found that one, cap-ET, efficaciously evoked TRPV1-dependent entry of Ca 2+ or the large cationic dye YO-PRO-1 comparably to capsaicin, but far smaller electrical currents. Cap-ETinduced YO-PRO-1 transport required permeation of both the agonist and the dye through the TRPV1 pore and could be enhanced by kinase activation or oxidative covalent modification. Moreover, cap-ET reduced capsaicin-induced currents by a voltage-dependent block of the pore. A low dose of cap-ET elicited entry of permanently charged Na + channel blockers to effectively suppress Na + currents in sensory neurons presensitized with oxidative chemicals. These results implicate therapeutic potential of these unique TRPV1 agonists exhibiting activity-dependent ion transport but of minimal pain-producing risks.activity-dependent capsaicinoids | hyperalgesia | ion permeation | selective analgesia C apsaicin, a small lipophilic molecule from hot chili peppers, acts on sensory neurons by opening the TRPV1 channel. TRPV1 is activated by noxious temperatures (>43°C) and serves as an integrator for major pain-producing signals (1, 2). Inflammatory hyperalgesia is dramatically reduced in mice lacking TRPV1 (3, 4). Besides being an attractive target for pain management, TRPV1 regulates autonomic function, such as body temperature, blood vessel tone, and release of transmitters from sensory nerves (5-9). TRPV1 activated by capsaicin at a concentration far below the pain-producing threshold triggers neuropeptide release (7) and production of other second messengers (10). In light of the complexity of TRPV1 actions in physiology, one major challenge in developing TRPV1-based pain treatment is to target therapeutic compounds to selectively inhibit hyperactive nociceptive neurons while sparing nerves of normal thresholds for pain detection.Capsaicin is among the most powerful chemical agonists of TRPV1. Being small and hydrophobic, capsaicin crosses the plasma membrane readily to reach its intracellular ligand-binding site on TRPV1 (11, 12), leading to channel activation and cation permeation. TRPV1 activation rapidly depolarizes nerves to evoke acute pain sensation and allows Ca 2+ entry to initiate downstream signaling events such as neuropeptide release or production of other second messengers. Nevertheless, TRPV1 activation facilitates cellular transport of organic cations such as tetraethylammonium (TEA), N-methylglucamine (NMG) (13), and the quaternary ammonium Na + channel blocker QX-314 (14) or even larger fluor...

“…However, thermal TRP channels have evolved to have tightly coupled enthalpy and entropy changes so that the free energy change is relatively small (7). The threshold of activation summarizes the influence of all the temperature-insensitive processes that can regulate gating including the membrane potential (5,6,10) and any other allosteric sources such as ligand binding.…”

mentioning

confidence: 99%

Modular thermal sensors in temperature-gated transient receptor potential (TRP) channels

Yao

Liu

Feng

2011

203

204

The molecular basis of the thermal sensitivity of temperature-sensitive channels appears to arise from a specific protein domain rather than integration of global thermal effects. Using systematic chimeric analysis, we show that the N-terminal region that connects ankyrin repeats to the first transmembrane segment is crucial for temperature sensing in heat-activated vanilloid receptor channels. Changing this region both transformed temperature-insensitive isoforms into temperature-sensitive channels and significantly perturbed temperature sensing in temperature-sensitive wild-type channels. Swapping other domains such as the transmembrane core, the C terminus, and the rest of the N terminus had little effect on the steepness of temperature dependence. Our results support that thermal transient receptor potential channels contain modular thermal sensors that confer the unprecedentedly strong temperature dependence to these channels. chimera | temperature gating | temperature jump | thermosensation | pain T he ability to sense temperature is vital to living organisms. In mammals, the neural input on ambient temperature results from specialized groups of neurons that project to the skin. The transducers involve ion channels known as transient receptor potential (TRP) channels (1, 2), which constitute an array of biological thermometers responsive over a broad temperature gradient from noxious cold to noxious hot (3).The molecular mechanism by which temperature changes induce channel opening is not yet known, but the phenomenological tools to analyze the system are known from classical thermodynamic theory. The probability of channel opening follows a Boltzmann relationship to temperature. The enthalpy change (ΔH) between closed and open determines the slope sensitivity of the curve, whereas the entropy change (ΔS) affects its midpoint (T 1∕2 ). The term "threshold" is also commonly used in studies of temperature-sensitive channels to represent the change in temperature required for the response to be larger than the noise level of the recording. Changes in threshold could occur by changes in ∆H or T 1∕2 or the recording noise level.Thermodynamic analyses reveal that thermal TRP channels undergo large enthalpy changes, which accounts for their high temperature sensitivity (4-8). The opening of TRPV1, for example, involves an activation enthalpy of approximately 100 kcal/mol (7), five times the enthalpy change for ligand-or voltage-dependent gating [Q 10 ∼ 2-3 (ref. 9), equivalent to an enthalpy of approximately 20 kcal/mol]. If the free energy change were determined by enthalpy alone, the rate of gating would be very slow because the barrier would be too high. However, thermal TRP channels have evolved to have tightly coupled enthalpy and entropy changes so that the free energy change is relatively small (7). The threshold of activation summarizes the influence of all the temperature-insensitive processes that can regulate gating including the membrane potential (5, 6, 10) and any other allosteric sources such as li...