And so these IP three molecules, the nosatoll one, four, five triphosphates, go on and bind onto a special location on these ligand gated calcium channels. And when they bind, they cause a conformational change that opens up that internal passageway. And now what happens is because we have a high calcium concentration in the Er lumen and a low concentration in the cytoplasm, it causes these calcium ions to move down their electrochemical gradient from the lumen into the cytoplasm. And these calcium ions do two different things. Number one, the calcium ions find a ubiquitous protein molecule we call calmodulant. And we'll discuss the specifics of what calmodulen does and what it looks like in a future lecture.