Channel Proteins

• Water-filled pore in membrane allowing diffusion of charged substances across the membrane; change permeability to certain ions (e.g. Na^+, K^+, Ca^2^+,Cl^- )
• Aquaporins: For water transport; inner part of the channel is hydrophilic, there are many in the kidney - where large volumes of water need to be transported quickly
• Most channels are gated (opened/closed), allowing cells to control entry/exit; found in axons of neurons (nervous system) - types: Voltage-gated, Ligand-gated and Mechanically-gated