FIGURE 11-32 Dissolution of bone by polarized osteoclast cells requires a V-class proton pump and the ClC-7 chloride channel. The osteoclast plasma membrane is divided into two domains separated by the tight seal between a ring of membrane and the bone surface. The membrane domain facing the bone contains V-class proton pumps and ClC-7 Cl⁻ channels. The opposing membrane domain contains anion antiporters that exchange HCO₃⁻ and Cl⁻ ions. The combined operation of these three transport proteins and carbonic anhydrase acidifies the enclosed space and allows bone resorption while maintaining the neutral pH of the cytosol. See R. Planells-Cases and T. Jentsch, 2009, Biochim. Biophys. Acta 1792:173 for discussion of ClC-7.