Plasma membrane transporters serve to (i) provide cells with sufficient amounts of potassium; (ii) maintain the potassium homeostasis; (iii) eliminate toxic sodium (lithium) cations; (iv) preserve the membrane potential; (v) regulate the intracellular pH; (vi) keep a positive turgor inside the cell, which is necessary for plasma membrane/cell wall expansion and cell division, and (vii) cope with osmotic stress. There are six different well-characterized transporters at the plasma membrane. They comprise the potassium uptake systems Trk1 and Trk2, the potassium channel Tok1, the Pi-Na+ symporter Pho89, and the efflux systems Ena Na+-ATPases and Nha1 Na+/H+ antiporter. Besides these six specific alkali metal cation transporters, there is a cationic channel whose existence has been experimentally proven but whose gene has not been identified yet (NSC1) and several other (nonspecific) proteins/transporters marginally involved in potassium and/or sodium fluxes across the plasma membrane.