Several other transporters and ion channels play a role in generating a proton electrochemical gradient. One is TPK 3, a potassium channel that is activated by Ca and conducts K from the thylakoid lumen to the stroma, which helps establish the electric field. On the other hand, the electro-neutral K efflux antiporter (KEA 3) transports K into the thylakoid lumen and H into the stroma, which helps establish the pH gradient.