Trpv5: A ca2+ channel for the fine-tuning of ca2+reabsorption

Abstract

TRPV5 is one of the two channels in the TRPV family that exhibit high selectivity to Ca2+ ions. TRPV5 mediates Ca2+ influx into cells as the first step to transport Ca2+ across epithelia. The specialized distribution in the distal tubule of the kidney positions TRPV5 as a key player in Ca2+ reabsorption. The responsiveness in expression and/or activity of TRPV5 to hormones such as 1,25-dihydroxyvitamin D3, parathyroid hormone, estrogen, and testosterone makes TRPV5 suitable for its role in the fine-tuning of Ca2+ reabsorption. This role is further optimized by the modulation of TRPV5 trafficking and activity via its binding partners; co-expressed proteins; tubular factors such as calbindin- D28k, calmodulin, klotho, uromodulin, and plasmin; extracellular and intracellu- lar factors such as proton, Mg2+, Ca2+, and phosphatidylinositol-4,5- bisphosphate; and fluid flow. These regulations allow TRPV5 to adjust its overall activity in response to the body’s demand for Ca2+ and to prevent kidney stone formation. A point mutation in mouse Trpv5 gene leads to hypercalciuria similar to Trpv5 knockout mice, suggesting a possible role of TRPV5 in hypercalciuric disorders in humans. In addition, the single nucleotide polymorphisms in Trpv5 gene prevalently present in African descents may contribute to the efficient renal Ca2+ reabsorption among African descendants. TRPV5 represents a potential therapeutic target for disorders with altered Ca2+ homeostasis.