We have different types of proteins that basically move different types of molecules across our membrane. Now, this is the apical side. This is this side of the membrane that points towards the lumen of the proximal convoluted tubule. So this is where our filtrate is actually found. So as the filtrate moves this way, we have the passive and active transport of different types of molecules and ions. So the first transport that we should discuss is found on this protein membrane.