The function of KCNQ2 (potassium voltage-gated channel subfamily Q member 2, ENSG00000075043) is as follows. Pore-forming subunit of the voltage-gated potassium (Kv) M- channel which is responsible for the M-current, a key controller of neuronal excitability (PubMed:24277843, PubMed:28793216, PubMed:9836639). M-channel is composed of pore-forming subunits KCNQ2 and KCNQ3 assembled as heterotetramers (PubMed:10781098, PubMed:14534157, PubMed:32884139, PubMed:37857637, PubMed:9836639). The native M-current has a slowly activating and deactivating potassium conductance which plays a critical role in determining the subthreshold electrical excitability of neurons as well as the responsiveness to synaptic inputs (PubMed:14534157, PubMed:28793216, PubMed:9836639). KCNQ2-KCNQ3 M-channel is selectively permeable in vitro to other cations besides potassium, in decreasing order of affinity K(+) > Rb(+) > Cs(+) > Na(+) (PubMed:28793216). M-channel association with SLC5A3/SMIT1 alters channel ion selectivity, increasing Na(+) and Cs(+) permeation relative to K(+) (PubMed:28793216). Suppressed by activation of the muscarinic acetylcholine receptor CHRM1 (PubMed:10684873, PubMed:10713961). {ECO:0000269|PubMed:10684873, ECO:0000269|PubMed:10713961, ECO:0000269|PubMed:10781098, ECO:0000269|PubMed:14534157, ECO:0000269|PubMed:24277843, ECO:0000269|PubMed:28793216, ECO:0000269|PubMed:32884139, ECO:0000269|PubMed:37857637, ECO:0000269|PubMed:9836639}.