FIGURE 3.

Maturation of inhibitory neurotransmission is dependent on chloride channel expression

During development, the opening of ionotropic chloride channels due to GABAergic or glycinergic receptor activation (glycine receptor pentamers with gephyrin clustering shown in orange) leads to chloride efflux (blue arrows) from the neuron, depolarizing the membrane (black bilayer). This is due to high intracellular chloride concentrations (~30 mM) engendered by the abundant expression of NKCC1 chloride transporter (teal) and low expression of the KCC2 chloride transporter (green). The relative expression of these transporters reverses during later postnatal neuronal maturation, such that KCC2 becomes much more abundant and NKCC1 expression is negligible. As a result, internal chloride concentrations in mature neurons is much lower (~5 mM), such that GABAergic or glycinergic receptor activation leads to influx of chloride through ionotropic channels and the hyperpolarization of the membrane. Note that potassium (and sodium in NKCC1) is also co-transported through these channels (yellow arrows).