Probable calcium-activated potassium channel. Homotetramer. Expressed in hydathodes and the vascular tissues of roots, stems, leaves and flowers. The pore-forming region (also called P-domain or P-loop) is enclosed by two transmembrane segments (1P/2TM) and contains a pseudo GYGD signature motif such as GYFD which seems to be involved in potassium selectivity. Belongs to the two pore domain potassium channel (TC 1.A.1.7) family. KCO3 shares similarity to the TPK family (2P/4TM) but lacks the conserved internal part including one pore-forming region and two transmembrane segments. As a result and according to its structure, KCO3 could also be classified as a member of the IRK family (1P/2TM).