A role for the cystic fibrosis transmembrane conductance regulator in the nitric oxide-dependent release of Cl- from acidic organelles in amacrine cells

Gamma-amino butyric acid (GABA) and glycine typically mediate synaptic inhibition because their ligand-gated ion channels support the influx of Cl^-. However, the electrochemical gradient for Cl^- across the postsynaptic plasma membrane determines the voltage response of the postsynaptic cell. Typically low cytosolic Cl^- supports inhibition while higher levels of cytosolic Cl^- can suppress inhibition or promotes depolarization. We previously reported that nitric oxide (NO) releases Cl^- from acidic organelles and transiently elevates cytosolic Cl^- making the response to GABA and glycine excitatory. Here, we test the hypothesis that the cystic fibrosis transmembrane conductance regulator (CFTR) is involved in the NO-dependent efflux of organellar Cl^-. We first establish the mRNA and protein expression of CFTR in our model system, cultured chick retinal amacrine cells. Using whole cell voltage clamp recordings of currents through GABA-gated Cl^- channels, we examine the effects of pharmacological inhibition of CFTR on the NO-dependent release of internal Cl-. To interfere with the expression of CFTR, we used clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 genome editing. We find that both pharmacological inhibition and CRISPR/Cas9-mediated knockdown of CFTR blocks the ability of NO to release Cl^- from internal stores. These results demonstrate that CFTR is required for the NO-dependent efflux of Cl^- from acidic organelles.

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