CHloride and brain

 Astrocytes are the most abundant cell type in the CNS (central nervous system). They exert multiple functions during development and in the adult CNS that are essential for brain homeostasis. Both cation and anion channel activities have been identified in astrocytes and it is believed that they play key roles in astrocyte function

Chloride is the main physiological anion, serving as the principal compensatory ion for the movement of major cations such as Na+, K+ and Ca2+

. Regarding the importance of Cl− in the CNS, the functions attributed to chloride channels include the control of membrane potential, cell volume homeostasis and regulation of cell proliferation and apoptosis

The GABA_A receptor (GABA_AR) is an ionotropic receptor and ligand-gated ion channel. Its endogenous ligand is γ-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the central nervous system. Upon opening, the GABA_A receptor on the postsynaptic cell is selectively permeable to chloride ions (Cl⁻) and, to a lesser extent, bicarbonate ions (HCO₃⁻).^[1][2] Depending on the membrane potential and the ionic concentration difference, this can result in ionic fluxes across the pore. If the membrane potential is higher than the equilibrium potential (also known as the reversal potential) for chloride ions, when the receptor is activated Cl⁻ will flow into the cell.^[3] This causes an inhibitory effect on neurotransmission by diminishing the chance of a successful action potential occurring at the postsynaptic cell. The reversal potential of the GA