Channels (pores) transport various substances across biological membranes, which are a natural barrier between cells and the environment. Channels are formed by protein complexes whose size can reach 120 nm. Depending on the type their internal diameter can range from 0.5 nm (ion channels) to 40 nm (nuclear pores). In molecular biology the term “channel” refers to structures transporting ions, while the term “pore” refers to structures for the passage of large molecules.

Transport through the channels can be passive (diffusion along the concentration gradient) and active (uses energy). Often the channels demonstrate selectivity to the size of the transferred substances. A striking example of such size effect is represented by the channels for transfer of sodium and potassium cations. Due to differences in the size of cations some channels provide efficient transport of potassium, but retain sodium cations, while the others, on the contrary, transport sodium cations and retain potassium cations.

Channels and pores are regulated structures, i.e. their formation, diffusion through the membrane and activity are regulated. They play an important functional role in the physiology of cells and subcellular compartments (nuclei, mitochondria, etc.), and in cell death. A striking example of the regulation and importance of pores is their controlled formation in the outer mitochondrial membrane. Assembling of these pores occurs in response to intracellular signals of serious damage to cellular structures (such as DNA) and leads to the release of mitochondrial proteins, triggering programmed cell death.

In nanobiotechnology the channels are used for the construction of biosensors and for the development of devices for controlled drug release in the drug delivery systems.