A uniporter is an integral membrane protein that transports a single type of substrate species (charged or uncharged) across a cell membrane. It may use either facilitated diffusion and transport along a diffusion gradient or transport against one with an active transport process.. They can be either ion channels or carrier proteins. A uniporter is an integral membrane protein that transports a single type of substrate species (charged or uncharged) across a cell membrane. It may use either facilitated diffusion and transport along a diffusion gradient or transport against one with an active transport process.. They can be either ion channels or carrier proteins. Uniporter carrier proteins work by binding to one molecule of substrate at a time. Uniporter channels open in response to a stimulus and allow the free flow of specific molecules.