Jonkanaler

Jonkanaler, or ion channels, are transmembrane proteins that form selective pores allowing ions such as sodium, potassium, calcium, and chloride to pass across cell membranes. They enable rapid changes in membrane potential and are essential for electrical signaling in neurons and muscle, as well as for secretory processes and the maintenance of ionic balance in cells.

Most jonkanaler are built from subunits that assemble to create a conductive pore. Some channels are tetrameric, with four identical or similar subunits surrounding the pore, while others consist of a single polypeptide with four homologous domains. Ion selectivity is determined by specific regions within the pore, and gating—the opening and closing of the channel—is controlled by sensors that respond to voltage, ligands, mechanical force, temperature, or a combination of factors. Auxiliary subunits and cellular signaling can modulate channel activity and expression.

Ion channels are commonly classified by their gating mechanism: voltage-gated channels open in response to changes in membrane potential; ligand-gated channels respond to neurotransmitters or other molecules; mechanosensitive channels respond to membrane stretch or pressure; and temperature-sensitive channels respond to thermal changes. They include channels for sodium, potassium, calcium, and chloride ions, and play key roles in action potential generation, synaptic transmission, muscle contraction, hormone and enzyme secretion, and regulation of cellular excitability.

Dysfunction of jonkanaler can lead to channelopathies, a broad group of disorders. Examples include epilepsies and ataxias linked to mutations in voltage-gated sodium or potassium channels, and cystic fibrosis involving a chloride channel. Pharmacological agents often target ion channels to modulate excitability in treatments for pain, arrhythmias, and other conditions.