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Summary: It is well established that ligand-gated chloride flux across the plasma membrane modulates neuronal excitability. We find that a voltage-dependent Cl− conductance increases neuronal excitability in immature rodents as well, enhancing the time course of NMDA receptor-mediated miniature excitatory postsynaptic potentials (mEPSPs). This Cl− conductance is activated by CaMKII, is electrophysiologically identical to the CaMKII-activated CLC-3 conductance in nonneuronal cells, and is absent in clc-3−/− mice. Systematically decreasing [Cl−]i to mimic postnatal [Cl−]i regulation progressively decreases the amplitude and decay time constant of spontaneous mEPSPs. This Cl−-dependent change in synaptic strength is absent in clc-3 −/− mice. Using surface biotinylation, immunohistochemistry, electron microscopy, and coimmunoprecipitation studies, we find that CLC-3 channels are localized on the plasma membrane, at postsynaptic sites, and in association with NMDA receptors. This is the first demonstration that a voltage-dependent chloride conductance modulates neuronal excitability. By increasing postsynaptic potentials in a Cl− dependent fashion, CLC-3 channels regulate neuronal excitability postsynaptically in immature neurons. [Copyright &y& Elsevier]

Summary: Cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-regulated chloride channel localized at apical cell membranes and exists in macromolecular complexes with a variety of signaling and transporter molecules. Here, we report that the multidrug resistance protein 4 (MRP4), a cAMP transporter, functionally and physically associates with CFTR. Adenosine-stimulated CFTR-mediated chloride currents are potentiated by MRP4 inhibition, and this potentiation is directly coupled to attenuated cAMP efflux through the apical cAMP transporter. CFTR single-channel recordings and FRET-based intracellular cAMP dynamics suggest that a compartmentalized coupling of cAMP transporter and CFTR occurs via the PDZ scaffolding protein, PDZK1, forming a macromolecular complex at apical surfaces of gut epithelia. Disrupting this complex abrogates the functional coupling of cAMP transporter activity to CFTR function. Mrp4 knockout mice are more prone to CFTR-mediated secretory diarrhea. Our findings have important implications for disorders such as inflammatory bowel disease and secretory diarrhea. [Copyright &y& Elsevier]