Intracellular chloride concentration influences the GABAA receptor subunit composition.

GABA(A) receptors (GABA(A)Rs) exist as different subtype variants showing unique functional properties and defined spatio-temporal expression pattern. The molecular mechanisms underlying the developmental expression of different GABA(A)R are largely unknown. The intracellular concentration of chloride ([Cl(-)](i)), the main ion permeating through GABA(A)Rs, also undergoes considerable changes during maturation, being higher at early neuronal stages with respect to adult neurons. Here we investigate the possibility that [Cl(-)](i) could modulate the sequential expression of specific GABA(A)Rs subtypes in primary cerebellar neurons. We show that [Cl(-)](i) regulates the expression of α3-1 and δ-containing GABA(A) receptors, responsible for phasic and tonic inhibition, respectively. Our findings highlight the role of [Cl(-)](i) in tuning the strength of GABAergic responses by acting as an intracellular messenger.