Integral membrane subunit of the KtrCD potassium uptake transporter. The 2 major potassium transporter complexes KtrAB and KtrCD confer resistance to both suddenly imposed and prolonged osmotic stress. Homodimer. Part of the KtrCD complex formed by an octameric catalytic ring of KtrC and a membrane associated dimer of KtrD forming a potassium channel (By similarity). Impaired potassium uptake. Belongs to the TrkH potassium transport family. Ktr (TC 2.A.38.4) subfamily.