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.