Well, within this restricted region of the cavity, we basically have a five amino acid sequence known as a selectivity filter on each side of that potassium ion. So one on the left side and one on the right side. So we have the sequence of three anion, valine, glycine, tyrosine, and glycine on this side as well as on this side. And the reason we have these identical sequences is because we have four of these identical polypeptide chains that create this tetrameric structure. And so what happens is one of the functions of the selectivity filter, this sequence of five amino acids, is that they're oriented in such a way so that the Carbonal oxygen atoms, these atoms show the red of these residues. These amino acids basically orient themselves in such a way as to form stabilizing directions between the partially negative charges of the oxygen and the false positive charges on those potassium ions.