A thermodynamic framework for understanding temperature sensing by transient receptor potential (TRP) channels

Abstract

The exceptionally high temperature sensitivity of certain transient receptor potential (TRP) family ion channels is the molecular basis of hot and cold sensation in sensory neurons. The laws of thermodynamics dictate that opening of these specialized TRP channels must involve an unusually large conformational standard-state enthalpy, ΔH(o): positive ΔH(o) for heat-activated and negative ΔH(o) for cold-activated TRPs. However, the molecular source of such high-enthalpy changes has eluded neurobiologists and biophysicists. Here we offer a general, unifying mechanism for both hot and cold activation that recalls long-appreciated principles of protein folding. We suggest that TRP channel gating is accompanied by large changes in molar heat capacity, ΔC(P). This postulate, along with the laws of thermodynamics and independent of mechanistic detail, leads to the conclusion that hot- and cold-sensing TRPs operate by identical conformational changes.

Fig. 1.

Temperature dependence of conformational equilibrium constant. The behavior of Eq. 1 is shown for indicated values of ΔC_P (kcal/mol-K), with K_o = 0.01 and T_o = 25 °C (arrow). Dashed line marks the half-activation level of the equilibrium.

Fig. 2.

Modulation of temperature sensing. Temperature dependence of either lnK (Left, Eq. 10) or open probability (Right, Eq. 2B) is plotted for ΔC_P = 4 kcal/mol-K and two values of T_o: 21 °C (red, mimicking hot-activating channel) or 29 °C (blue, mimicking cold-activating channel). Dashed regions of the curves mark ranges where channels are likely to be experimentally inaccessible.