Anoctamin 1 (Ano1) is an intrinsic constituent of Ca²⁺ acivated Cl^- channels (CaCC) expressed in several epithelial tissues and also smooth muscle cells. Loss of Ano1 causes a defect in epithelial Ca²⁺-dependent chloride transport in knockout (KO) mice. Here we investigated the physiological significance of Ano1 for renal function. Expression of Ano1 in human and mouse kidneys was confirmed by RT-PCR in total RNA and by Western blot. Immunofluorescence in mouse kidneys showed apical expression of Ano1 in proximal tubular epithelial cells, where it colocalized with cubulin. Expression was also detected in glomeruli. Urine samples from wt- and Ano1-KO mice revealed high molecular weight proteinuria. Electron microscopy of WT- and Ano1-KO kidney slices showed accumulation of intracellular vesicles in proximal tubular epithelial cells. Because Ano1-KO causes multiple organ defects which may also indirectly affect kidney function, we generated floxed Ano1 mice. To differentiate between a deficiency in glomerular filtration and proximal tubular protein re-absorption, we generated a podocyte-specific Ano1-KO: Ano1 f^lox/flox;Nphs2-cre⁺. Podocytes from Ano1 f^lox/flox;Nphs2-cre⁺ showed no obvious ultra-structural changes and no morphological differences were detected on the glomerular filtration barrier. Also, urine protein concentration and GFR were not different between WT and KO mice. These results suggests that proteinuria in Ano1 KO mice is not due to dysfunction of podocytes.

(Supported by DFG/SFB699, DF: PhD fellowship SFRH/BD/43313/2008)