Fig. 2.

The mechanism of Ca²⁺ absorption in the renal epithelium. Transcellular Ca²⁺ reabsorption in the distal convoluted tubule (DCT) and connecting tubule (CNT) occurs by three steps; (i) entry of Ca²⁺ through the calcium channels [transient receptor potential vanilloid (TRPV) 5, TRPV6] in the apical membrane, (ii) binding of Ca²⁺ with calcium-binding protein (calbindin) and diffusion in the cytoplasm (without significant change in the intracellular i[Ca²⁺]), and (iii) Ca²⁺ extrusion via an ATP-dependent Ca²⁺-ATPase (PMCA1b) or an Na²⁺/Ca²⁺ exchanger (NCX1) in the basolateral membrane.