The ability of KCNQ (Kv7) channels to form hetero-oligomers is of high physiological importance, since KCNQ3 heteromers with KCNQ2 and likely also KCNQ5 underlie the neuronal M-current, which modulates neuronal excitability. We have recently identified that the TCC2 domain mediate the selectivity of KCNQ2/KCNQ3 heteromultimeric interactions, with structural integrity of TCC2 from KCNQ2 being most important. Interestingly, co-expression of KCNQ3 in Xenopus oocytes with a c-terminal protein fragment of KCNQ2 that contains the second TCC domain lead to an increase of currents in Two-Electrode-Voltage clamp experiments compared to KCNQ3 alone. To test, whether this fragment modifies the pore properties of the KCNQ3 channel, we studied the effect of TEA and Retigabine (RGB) on currents generated by KCNQ2 and the KCNQ2 fragment. Our data demonstrate that the c-terminal protein fragment of KCNQ2 alters the KCNQ3 pore properties.