kloridtransport

Kloridtransport refers to the movement of chloride ions (Cl−) across biological membranes or within chemical systems. It is essential for maintaining electrochemical gradients, osmolality, acid–base balance, and fluid secretion. Chloride ions move mainly through channels, exchangers, and cotransporters, or by pump-coupled mechanisms.

Mechanisms: Passive diffusion occurs via chloride channels, including voltage-gated and ligand-gated channels, as well as CFTR, a channel-forming protein in the family of ABC transporters. Cl−/HCO3− exchangers (anion exchangers such as AE1) swap chloride for bicarbonate, contributing to pH regulation and CO2 transport. Active transport uses cotransporters such as NKCC (Na+/K+/2Cl−) and NCC (Na+/Cl−), which move chloride together with sodium and other ions; these transporters are common in epithelia and are targets of diuretics. Cl− pumps and other regulatory mechanisms exist in various tissues to maintain chloride homeostasis.

Physiology: In neurons, chloride gradients influence the strength of inhibitory neurotransmission through GABA_A and glycine receptors. In epithelia, chloride transport drives salt and water movement, affecting airway and intestinal secretions and kidney function. In red blood cells, the chloride shift (AE1-mediated exchange of Cl− and HCO3−) facilitates CO2 transport.

Clinical relevance: Defects in chloride transport are central to cystic fibrosis, where CFTR dysfunction impairs chloride secretion and mucus clearance. Abnormal chloride handling also appears in renal, neurological, and respiratory disorders. Studying chloride transport uses electrophysiology, chloride-sensitive indicators, flux assays, and structural analyses of channels and exchangers.