 Specifically, scientists were able to conclude that human TPC are predominantly voltage-dependent sodium channels, and that PI(3,5)P2, an endolysosome-specific phosphoinositide (PIP), is a direct activator of TPC channels while NAADP is actually not an activator as it was once previously assumed to be.At the mouth of the TPC pore, there are four amino acid residues with negative charges that can interact with ions that pass through.This site is too wide to select ions.