Clues to understanding cold sensation: Thermodynamics and electrophysiological analysis of the cold receptor TRPM8

Abstract

The cold and menthol receptor, TRPM8, also designated CMR1, is a member of the transient receptor potential (TRP) family of excitatory ion channels. TRPM8 is a channel activated by cold temperatures, voltage, and menthol. In this study, we characterize the coldand voltage-induced activation of TRPM8 channel in an attempt to identify the temperature-and voltage-dependent components involved in channel activation. Under equilibrium conditions, decreasing temperature has two effects. Since the breakthrough identification of the vanilloid receptor, TRPV1, as the hot-capsaicin receptor (1), six temperature-dependent channels have been cloned during the last 7 years (1-8). Interestingly, all of the cloned channels belong to the extended transient receptor potential (TRP) family of excitatory channels (9, 10). TRP channels are membrane proteins constituted by subunits containing six-transmembrane domains, which assemble into tetramers forming conducting pores (11, 12). Heat-dependent channels belong to the vanilloid receptor TRPV subfamily and the cold-dependent channel TRPM8 belongs to the TRPM subfamily (13). Thermo-TRP channels have different temperature thresholds for activation, and their activity is modulated by several different agonists, allowing us to sense and differentiate a large spectrum of temperatures, from below 0°C to 50°C (14). Among those temperature-activated channels, TRPM8 was the first found to sense a cold stimulus (4, 7). TRPM8 is a nonselective outwardly rectifying channel. The channel opens at Ϸ28°C, and its activity increases as the temperature diminishes and saturates at Ϸ10°C (4). The channel is also able to respond to several agonists, including menthol (15).Channel gating is known to be affected by temperature. Q 10 value is used to estimate the temperature dependence of a given system. Channels with a Q 10 Ն 2 are considered highly temperature-dependent (16). Thermo-TRP receptor channels present exceptionally high Q 10 values (Ͼ20) (13).Several studies have addressed capsaicin binding (17, 18), pH dependencies (19), physiological relevance (13), and, recently, thermodynamics (20) of TRPV1, one of the molecular transducers of heat sensation. Large values for transitional entropy, enthalpy, and Q 10 were found, (20) indicating large rearrangements in the channel structure during activation. In contrast, little is known about regulation of its counterpart, TRPM8.Here we show that the large changes in TRPM8 channel gating induced by temperature are mainly due to modifications of the maximum probability of opening and to a shift along the voltage axis of the conductance-voltage curves. Moreover, the results can be fully explained by using an allosteric model in which temperature has only a moderate effect on the voltage sensors (Q 10 Ϸ 3) when channels are closed. Thus, temperature and voltage sensor activation act almost independently to promote channel opening. MethodsTemperature Control and Ramps. The recording chamber consisted of an electrically isolated bronze block with a hole of the...

The varitint-waddler (Va) deafness mutation in TRPML3 generates constitutive, inward rectifying currents and causes cell degeneration

“…5a). Thus, the outward rectification of TRPML3, like that of other TRP channels (13)(14)(15)(16), is probably due to a voltage-sensitive increase in open probability (Fig. 4b).…”

“…4b and 5b). The outward rectification characteristic of many TRP channels, including wild-type TRPML3, results from a weak voltage sensitivity: Open probability increases with ''depolarization'' at positive membrane potentials, in the nonphysiological range (13)(14)(15)(16) (Fig. 4b).…”

“…4b). Activation of some of these TRP channels by physical stimuli such as temperature or by ligand binding shifts their voltage sensitivity toward negative potentials, so that channels open in the physiological range of membrane resting potentials (13)(14)(15)(16). However, these channels still display outward rectification, because their open probability increases with depolarization.…”

Cysteine-rich secretory protein 4 is an inhibitor of transient receptor potential M8 with a role in establishing sperm function

“…Several TRP channels have been localized to mouse or human sperm, including TRPC1-6 and TRPM8 (25,29,30). Given our recent data demonstrating the localization and functional analysis of TRMP8 on mouse sperm (27) and the considerable similarity of the current data to earlier investigations (26), we chose to analyze the affect of CRISP4 on TRPM8 in the first instance.…”

“…These data raise the potential for CRISP4, via the regulation of ion channels, to impact upon several aspects of sperm function. In the present study, we chose to focus on the TRP channel subset of Ca 2+ conducting channels in mammalian sperm (25)(26)(27).…”