Extracellular Sodium is Required for Temperature-Dependent Gating in TRPV1 Channels

The TRPV1 channel in sensory neurons integrates pain-producing stimuli, including noxious temperature, acidosis, pungent vanilloid compounds and pro-inflammatory lipids. Measurements of TRPV1 channel activity at extreme positive and negative voltages in the presence of other stimuli suggest that the channel has a unique opening transition that is allosterically modulated by independent stimulus-sensing domains. On the contrary, recently obtained near-atomic resolution structures of TRPV1 in different states suggest that different agonists promote distinct open states, by differentially modulating the inner pore gate or the selectivity filter. Finally, it has been proposed that the opening of the pore may confer the channel with high temperature-sensitivity. Here we show that extracellular sodium ions tune both temperature-dependent activation and inactivation in TRPV1 channels to maintain sensitivity to noxious stimuli at physiological temperatures. Exploration of temperature-dependent activation over a wide range of temperatures in the presence of distinct modulators demonstrates that the gating mechanism involves temperature-sensitive and -insensitive transitions that are allosterically coupled and differentially modified by sodium, pH, vanilloids and tarantula toxins. We observe that the channels exhibit non-maximal open probability and temperature-independent gating in the absence of external sodium or in the presence of double knot tarantula toxin DkTx, indicating that the opening transition is temperature-independent and supporting the modular allosteric view of this channel protein. This unique gating mechanism provides a framework for understanding how the temperature sensitivity of TRPV1 is tuned by a wide array of regulators.