CLC-3 is widely distributed with prominent expression in tissues of neuroectoderm origin. In the brain, it is highly expressed in the hippocampus, olfactory bulb and olfactory cortex. The channel is also prominently expressed in aortic and coronary vascular smooth muscle cells, aortic endothelial cells and tracheal and alveolar epithelial cells.The physiological function of CLC-3 is not entirely clear, but it has been suggested that CLC-3 generates a shunt current of chloride for v-H+-ATPases, thereby aiding the acidification of endosomes and synaptic vesicles as well as lysosomes. Disruption of the ClC-3 gene in mice causes severe neuronal loss, leading to a complete loss of the hippocampus in adult mice. In addition, CLC-3 has been shown to have a critical role in the respiratory burst and phagocytosis of polymorphonuclear cells, a key cell type of innate host defense.