Voltage-independent, large conductance and potassium-selective tonoplast ion channel. Regulated by cytoplasmic calcium and pH. Does not mediate slow-vacuolar (SV) ionic currents, but essential to establish VK currents. Has some permeability for Rb(+) and NH(4)(+), but none for Na(+), Cs(+) or Li(+). Involved in intracellular K(+) redistribution and/or K(+) retranslocation between different tissues. Could be activated by protein kinase C (By similarity). Strongly induced by calcium. Blocked by barium, tetraethylammonium (TEA), quinine and quinidine. Homodimer. Interacts with GRF1 and GRF6, but only GRF6 modulates the channel activity. Tonoplast. Detected in mesophyll cells, guard cells and vascular tissues of the leaves. Expressed in the hilum, where the funiculus is attached during fruit maturation and in the embryo. Also expressed at a lower level in seedlings, root tips and elongation zones, and flowers. Could be detected in mitotically active tissues. 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. The C-terminus (328-363) is required for vacuolar targeting. Phosphorylation at Ser-42 increases and stabilizes the interaction with 14-3-3 proteins. Reduced growth in both high and low K(+) conditions. Slower germination and increased sensitivity to abscisic acid. Reduction of the total tonoplast current density. 14-3-3 protein binding is not involved in endoplasmic reticulum export and tonoplast targeting. Belongs to the two pore domain potassium channel (TC 1.A.1.7) family. Was initially described as an outward slow-vacuolar (SV) ion channel (PubMed:9184204 and PubMed:11821043).