Highly selective inward-rectifying potassium channel that is specifically located in the tonoplast of protein storage vacuoles. Functions independently of the voltage difference across the membrane. Homodimer. Tonoplast of protein storage vacuoles. Each of the two pore-forming region (also called P-domain or P-loop) is enclosed by two transmembrane segments (2P/4TM) and contains the GYGD signature motif which seems to be involved in potassium selectivity. Belongs to the two pore domain potassium channel (TC 1.A.1.7) family.