Contribution of the S5-pore-S6 domain to the gating characteristics of the cation channels TRPM2 and TRPM8.
Kühn FJ., Witschas K., Kühn C., Lückhoff A.
The closely related cation channels TRPM2 and TRPM8 show completely different requirements for stimulation and are regulated by Ca(2+) in an opposite manner. TRPM8 is basically gated in a voltage-dependent process enhanced by cold temperatures and cooling compounds such as menthol and icilin. The putative S4 voltage sensor of TRPM8 is closely similar to that of TRPM2, which, however, is mostly devoid of voltage sensitivity. To gain insight into principal interactions of critical channel domains during the gating process, we created chimeras in which the entire S5-pore-S6 domains were reciprocally exchanged. The chimera M2-M8P (i.e. TRPM2 with the pore of TRPM8) responded to ADP-ribose and hydrogen peroxide and was regulated by extracellular and intracellular Ca(2+) as was wild-type TRPM2. Single-channel recordings revealed the characteristic pattern of TRPM2 with extremely long open times. Only at far-negative membrane potentials (-120 to -140 mV) did differences become apparent because currents were reduced by hyperpolarization in M2-M8P but not in TRPM2. The reciprocal chimera, M8-M2P, showed currents after stimulation with high concentrations of menthol and icilin, but these currents were only slightly larger than in controls. The transfer of the NUDT9 domain to the C terminus of TRPM8 produced a channel sensitive to cold, menthol, or icilin but insensitive to ADP-ribose or hydrogen peroxide. We conclude that the gating processes in TRPM2 and TRPM8 differ in their requirements for specific structures within the pore. Moreover, the regulation by extracellular and intracellular Ca(2+) and the single-channel properties in TRPM2 are not determined by the S5-pore-S6 region.