Pore-forming subunit of a potassium efflux system that confers protection against electrophiles. Catalyzes K(+)/H(+) antiport. Can also export rubidium, lithium and sodium. Inhibited by glutathione. This inhibition is increased by NADH. Activated by adducts between glutathione and electrophiles. Homodimer. Interacts with the regulatory subunit KefF, forming a heterotetramer with 2:2 stoichiometry. Interaction with KefF is required for optimal activity. The active antiporter may be formed by the heterotetramer, or by an octamer. The cytoplasmic RCK N-terminal domain regulates channel activity. It binds glutathione, resulting in inhibition of potassium efflux. In contrast, binding of the adducts formed between glutathione and electrophiles leads to activation of potassium efflux. Is expected to bind NADH, but X-ray crystallography shows bound AMP, and it would be difficult to accommodate NADH in this binding site (PubMed:21041667). Belongs to the monovalent cation:proton antiporter 2 (CPA2) transporter (TC 2.A.37) family. KefC subfamily.