Unique actions of GABA arising from cytoplasmic chloride microdomains

Abstract

AbstractDevelopmental, cellular, and subcellular variations in the direction of neuronal Cl−currents elicited by GABAAreceptor activation have been frequently reported, and we found a corresponding variance in the reversal potential (EGABA) for individual interneurons synapsing on a single pyramidal cell. These findings suggest a corresponding variance in the cytoplasmic concentration of Cl−([Cl−i]). We determined [Cl−]iby: 1) two-photon imaging of the Cl−sensitive, ratiometric fluorescent protein SuperClomeleon (sCLM); 2) Fluorescence Lifetime IMaging (FLIM) of the Cl−sensitive fluorophore MEQ; and 3) electrophysiological measurements of EGABA. These methods collectively demonstrated stable [Cl−]imicrodomains in individual neuronsin vivo. Fluorometric and electrophysiological estimates of local [Cl−]iwere highly correlated. [Cl−]imicrodomains persisted after pharmacological inhibition of cation-chloride cotransporters (CCCs) but steadily decreased after inhibiting the polymerization of the anionic macromolecule actin. These studies highlight the existence of functionally significant neuronal Cl−microdomains that modify the impact of GABAergic inputs.