Membrane channels refer to the pores that are embedded with the lipid bilayer of cell membranes and in the membranes of organelles such as the nucleus, mitochondria, Golgi apparatus, endoplasmic reticulum, lysosomes, and chloroplasts. They are also called transmembrane channels. 

Membrane channels are formed by protein complexes that span the cell membrane, extending from the inner surface to the outer surface, connecting the extracellular matrix to the cytosol or cytoplasm.