Highly selective inward-rectifying potassium channel that could mediate potassium uptake in the pollen membrane. Plays an important role in pollen tube development. Assuming opened or closed conformations in response to the voltage difference across the membrane, the channel is activated by hyperpolarization. May interact with the cytoskeleton or with regulatory proteins. The potassium channel is probably composed of a homo- or heterotetrameric complex of pore-forming subunits. Predominantly expressed in flowers; especially in pollen. The segment S4 is probably the voltage-sensor and is characterized by a series of positively charged amino acids. The pore-forming region H5 is enclosed by the transmembrane segments S5 and S6 in the Shaker-type (1P/6TM) and contains the GYGD signature motif which seems to be involved in potassium selectivity. The KHA domain (rich in hydrophobic and acidic residues) present in the C-terminal part is likely to be important for tetramerization. Belongs to the potassium channel family. Plant (TC 1.A.1.4) subfamily. Was originally erroneously termed AKT5.