Figure 1.

Schematic representation of regulation and function of ClC-3 Cl⁻ channels in cardiac myocytes and vascular smooth muscle cells. ClC-3, a member of voltage-gated ClC Cl⁻ channel family, encodes Cl⁻ channels in cardiac myocytes and vascular smooth muscle cells that are volume regulated (I_{Cl, vol}) and can be activated by cell swelling (I_{Cl, swell}) induced by exposure to hypotonic extracellular solutions or possibly membrane stretch. I_{Cl, b} is a basally activated ClC-3 Cl⁻ current. Membrane topology model (α-helices a–r) for ClC-3 is modified from Dutzler et al¹⁰⁰. ClC-3 proteins are expressed on both sarcolemmal membrane and intracellular organelles including mitochondria (mito) and endosomes. The proposed model of endosome ion flux and function of Nox1 and ClC-3 in the signaling endosome is modified from Miller Jr et al¹⁰¹. Binding of IL-1β or TNF-α to the cell membrane initiates endocytosis and formation of an early endosome (EEA1 and Rab5), which also contains NADPH oxidase subunits Nox1 and p22phox, in addition to ClC-3. Nox1 is electrogenic, moving electrons from intracellular NADPH through a redox chain within the enzyme into the endosome to reduce oxygen to superoxide. ClC-3 functions as a chloride-proton exchanger, required for charge neutralization of the electron flow generated by Nox1. The ROS generated by Nox1 result in NF-κB activation. Both ClC-3 and Nox1 are necessary for generation of endosomal ROS and subsequent NF-κB activation by IL-1β or TNF-α in VSMCs. PKC, protein kinase C; PP, serine-threonine protein phosphatases; α-AR, α-adrenergic receptor; G_i, heterodimeric inhibitory G protein; Nox: NADPH oxidase; CaMKII: Ca²⁺/calmodulin-dependent protein kinase II; (+) stimulation; (–) inhibition.