Transportkanal

Transportkanal is the German term for a transmembrane protein that forms a pore allowing ions or small molecules to diffuse across a lipid bilayer. In English-language literature, these entities are usually called ion channels or water channels, depending on what they transport. Transportkanäle enable passive transport along electrochemical gradients, in contrast to transporters or carriers that bind substrates and undergo conformational changes to move them.

A key feature of transportkanäle is selectivity: they favor certain ions or molecules and exclude others. They are typically gated, meaning they switch between open and closed states in response to specific stimuli. Common gating mechanisms include changes in membrane potential (voltage-gated), binding of neurotransmitters or other ligands (ligand-gated), and mechanical forces such as membrane tension (mechanosensitive).

Major subclasses include voltage-gated ion channels (for potassium, sodium, calcium), ligand-gated ion channels (such as neurotransmitter receptors), and aquaporins, which specialize in water transport. Additional channels conduct anions like chloride or various metal ions. Structurally, many channels are formed by multiple subunits that assemble into a pore with a selectivity filter that determines ion preference and a gating region that controls opening.

Physiological roles are widespread: they underpin electrical signaling in nerve and muscle cells, regulate hormone and secretion processes, and contribute to osmoregulation and fluid balance. Dysfunctions of transportkanäle can lead to channelopathies and are frequent targets in pharmacology, with drugs modulating channel activity to treat pain, epilepsy, hypertension, and other conditions.