Views down (top) long and short channel axes, and (bottom) top-down through the central channel of AtTPC1 (PDB 5DQQ; ref. [20]). Boundaries for endolysosome/vacuole (E), membrane (M), and cytoplasm (C) are shown. Ca2+-ions, including the sites for luminal inhibition (Cai2+) and cytoplasmic activation (Caa2+), are shown as green spheres.