potassium ion transmembrane transporter activity solute:potassium antiporter activity Catalysis of the active transport of a potassium ion across a membrane by a mechanism whereby two or more species are transported in opposite directions in a tightly coupled process not directly linked to a form of energy other than chemiosmotic energy. potassium ion antiporter activity molecular_function GO:0022821 metal cation:monoatomic cation antiporter activity