Bidirectional shifts of TRPM8 channel gating by temperature and chemical agents modulate the cold sensitivity of mammalian thermoreceptors

Abstract

TRPM8, a member of the melastatin subfamily of transient receptor potential (TRP) cation channels, is activated by voltage, low temperatures and cooling compounds. These properties and its restricted expression to small sensory neurons have made it the ion channel with the most advocated role in cold transduction. Recent work suggests that activation of TRPM8 by cold and menthol takes place through shifts in its voltage-activation curve, which cause the channel to open at physiological membrane potentials. By contrast, little is known about the actions of inhibitors on the function of TRPM8. We investigated the chemical and thermal modulation of TRPM8 in transfected HEK293 cells and in cold-sensitive primary sensory neurons. We show that cold-evoked TRPM8 responses are effectively suppressed by inhibitor compounds SKF96365, 4-(3-chloro-pyridin-2-yl)-piperazine-1-carboxylic acid (4-tert-butyl-phenyl)-amide (BCTC) and 1,10-phenanthroline. These antagonists exert their effect by shifting the voltage dependence of TRPM8 activation towards more positive potentials. An opposite shift towards more negative potentials is achieved by the agonist menthol. Functionally, the bidirectional shift in channel gating translates into a change in the apparent temperature threshold of TRPM8-expressing cells. Accordingly, in the presence of the antagonist compounds, the apparent response-threshold temperature of TRPM8 is displaced towards colder temperatures, whereas menthol sensitizes the response, shifting the threshold in the opposite direction. Co-application of agonists and antagonists produces predictable cancellation of these effects, suggesting the convergence on a common molecular process. The potential for half maximal activation of TRPM8 activation by cold was ∼140 mV more negative in native channels compared to recombinant channels, with a much higher open probability at negative membrane potentials in the former. In functional terms, this difference translates into a shift in the apparent temperature threshold for activation towards higher temperatures for native currents. This difference in voltage-dependence readily explains the high threshold temperatures characteristic of many cold thermoreceptors. The modulation of TRPM8 activity by different chemical agents unveils an important flexibility in the temperature-response curve of TRPM8 channels and cold thermoreceptors.

N-Glycosylation of TRPM8 Ion Channels Modulates Temperature Sensitivity of Cold Thermoreceptor Neurons

“…Despite their intrinsic interest, these findings may not apply to a more physiological context. For example, we have found important differences in the gating properties of native and recombinant TRPM8 channels, leading to dramatic changes in voltage sensitivity and apparent thermal threshold (8). Moreover, others have reported differences in the glycosylation status of heterologously expressed and native TRPV1 channels (24).…”

Bidirectional Modulation of Thermal and Chemical Sensitivity of TRPM8 Channels by the Initial Region of the N-terminal Domain

“…TRPM8 is also gated by voltage, although with a weak voltage dependence. At high temperatures, or in the absence of chemical agonists, activation requires stronger depolarizations (13,17,18). In contrast, cooling or menthol application shift the voltage-activation curve of TRPM8 toward more negative voltages, increasing the open probability of the channel at physiological membrane potentials (13,18).…”

Transient receptor potential (TRP) cation channels

“…Activation of TRPM8 by depolarization is strongly temperature-dependent via a channel-closing rate that decreases with decreasing temperature. The V½ is shifted in the hyperpolarizing direction both by decreasing temperature and by exogenous agonists, such as menthol (Voets et al, 2004b) whereas antagonists produce depolarizing shifts in V½ (Mälkiä et al, 2007). The V½ for the native channel is far more positive than that of heterologously expressed TRPM8 (Mälkiä et al, 2007).…”