Renal expression of parvalbumin is critical for NaCl handling and response to diuretics

Abstract

The distal convoluted tubule (DCT) plays an essential role in the reabsorption of NaCl by the kidney, a process that can be inhibited by thiazide diuretics. Parvalbumin (PV), a Ca²⁺-binding protein that plays a role in muscle fibers and neurons, is selectively expressed in the DCT, where its role remains unknown. We therefore investigated the renal phenotype of PV knockout mice (Pvalb^−/−) vs. wild-type (Pvalb^+/+) littermates. PV colocalized with the thiazide-sensitive Na⁺-Cl⁻ cotransporter (NCC) in the early DCT. The Pvalb^−/− mice showed increased diuresis and kaliuresis at baseline with higher aldosterone levels and lower lithium clearance. Acute furosemide administration increased diuresis and natriuresis/kaliuresis, but, surprisingly, did not increase calciuria in Pvalb^−/− mice. NaCl supplementation of Pvalb^−/− mice increased calciuria at baseline and after furosemide. The Pvalb^−/− mice showed no significant diuretic response to hydrochlorothiazide, but an accentuated hypocalciuria. A decreased expression of NCC was detected in the early DCT of Pvalb^−/− kidneys in the absence of ultrastructural and apoptotic changes. The PV-deficient mice had a positive Ca²⁺ balance and increased bone mineral density. Studies in mouse DCT cells showed that endogenous NCC expression is Ca²⁺-dependent and can be modulated by the levels of PV expression. These results suggest that PV regulates the expression of NCC by modulating intracellular Ca²⁺ signaling in response to ATP in DCT cells. They also provide insights into the Ca²⁺-sparing action of thiazides and the pathophysiology of distal tubulopathies.