Extracellular Matrix Regulates Neuronal Chloride Concentration via K⁺-Cl⁻-Cotransporter 2

Abstract

The neuronal intracellular chloride concentration [Cl−]iis critical for γ-aminobutyric acid type A (GABAA) receptor-mediated transmission. Degradation of the extracellular matrix (ECM) is associated with raised [Cl−]ibut neither the mechanisms underlying this effect nor the consequences for GABA-mediated transmission are well understood. Hitherto it has been unclear how to reconcile the effect of the ECM on [Cl−]iwith the established role of cation-chloride cotransporters in setting [Cl−]i. In the present work we clarify the role of the ECM in the control of neuronal [Cl−]i. By measuring [Cl−]iin central neurons from male rats we show that the ECM affects basal [Cl−]ias well as the rate of Cl−extrusion after a high load. The mechanism is not via impermeant anions but through regulation of K+-Cl−-cotransporter 2 (KCC2). ECM degradation is accompanied by an N-type Ca2+-channel- and calpain-dependent reduction in the amount of KCC2 protein, increased basal [Cl−]i, reduced Cl−extrusion capacity as well as by reduced inhibitory, or even an excitatory, effect of intense GABAA-receptor mediated trans mission. This implies a previously unrecognized pathway for the control of neuronal [Cl−]iand excitability by the ECM.