Distribution of transcellular calcium and sodium transport pathways along mouse distal nephron.

The organization of Na(+) and Ca(2+) transport pathways along the mouse distal nephron is incompletely known. We revealed by immunohistochemistry a set of Ca(2+) and Na(+) transport proteins along the mouse distal convolution. The thiazide-sensitive Na(+)-Cl(-) cotransporter (NCC) characterized the distal convoluted tubule (DCT). The amiloride-sensitive epithelial Na(+) channel (ENaC) colocalized with NCC in late DCT (DCT2) and extended to the downstream connecting tubule (CNT) and collecting duct (CD). In early DCT (DCT1), the basolateral Ca(2+)-extruding proteins [Na(+)/Ca(2+) exchanger (NCX), plasma membrane Ca(2+)-ATPase (PCMA)] and the cytoplasmic Ca(2+)-binding protein calbindin D(28K) (CB) were found at very low levels, whereas the cytoplasmic Ca(2+)/Mg(2+)-binding protein parvalbumin was highly abundant. NCX, PMCA, and CB prevailed in DCT2 and CNT, where we located the apical epithelial Ca(2+) channel (ECaC1). Its subcellular localization changed from apical in DCT2 to exclusively cytoplasmic at the end of CNT. NCX and PMCA decreased in parallel with the fading of ECaC1 in the apical membrane. All three of them were undetectable in CD. These findings disclose DCT2 and CNT as major sites for transcellular Ca(2+) transport in the mouse distal nephron. Cellular colocalization of Ca(2+) and Na(+) transport pathways suggests their mutual interactions in transport regulation.