This is an outstanding video by medial illustrator, David Bolinsky, showing the activity of living human cells.  The actual video of the internal activity of the cell starts at 7:02 in the video.  

    Prior to that moment it's important to hear how Mr. Bolinsky describes the macrophages circulating in our blood, not knowing if a pathogen exists outside the vessel that the macrophage needs to destroy.  Mr. Bolinsky describes the attraction and how the macrophage changes shape to enter into the membrane wall.  This is another confirmation that ion channels are vessels of transport however the protein/particulate matter being transported has to be in the correct form.   A helical particle is larger than it would be if merely longitudinal.   Mass does matter in ion channels and the mass is the form of the matter allows, or restricts passage through the channel.