Channel proteins are integral proteins (also transmembrane proteins) which has pores that allow passage of water and hydrophilic solutes through the cell membrane.
some are open while others are gates that can be open or close in respond to different stimuli:
1. Ligand gate---> in respond to chemical
2. Voltage gate---> in respond ot electrical potential across the plasma membrane
3. Mechanical gate--> in respond to physical stress on a cell (strech,pressure)