Involvement of pore helix in voltage-dependent inactivation of TRPM5 channel

The transient receptor potential melastatin 5 (TRPM5) channel is a monovalent-permeable cation channel that is activated by intracellular Ca(2+). Expression of TRPM5 has been shown in taste cells, pancreas, brainstem and olfactory epithelium, and this channel is thought to be involved in controlling membrane potentials. In whole-cell patch-clamp recordings, TRPM5 exhibited voltage-dependent inactivation at negative membrane potentials and time constant of voltage-dependent inactivation of TRPM5 did not depend on the intracellular Ca(2+) concentrations between 100 and 500 nM. Alanine substitution at Y913 and I916 in the pore helix of TRPM5 increased time constant of voltage-dependent inactivation. Meanwhile, voltage-dependent inactivation was reduced in TRPM5 mutants having glycine substitution at L901, Y913, Q915 and I916 in the pore helix. From these results, we conclude that the pore helix in the outer pore loop might play a role in voltage-dependent inactivation of TRPM5.