Associates with and regulates the activity of the sodium/potassium-transporting ATPase (NKA) which catalyzes the hydrolysis of ATP coupled with the exchange of Na(+) and K(+) ions across the plasma membrane (PubMed:33231612). Reduces the apparent affinity for external K(+), an effect that depends on the presence of external Na(+) and voltage (PubMed:33231612). Increases the apparent affinity for intracellular Na(+) (PubMed:33231612). . This is the function of FXYD7 (FXYD domain containing ion transport regulator 7, ENSG00000221946).