Immunolocalization of relevant transport proteins in the 3D CCD. The 3D CCD expressed apical epithelial Na+ channel (ENaCα) (A), ENaCβ (B), large conductance BKα (C), aquaporin 2 (AQP2) (D), and basolateral Na+/K+-ATPase (E), consistent with native mammalian principal cells. ECM, extracellular matrix.