TRPC3 determines osmosensitive [Ca2+]i signaling in the collecting duct and contributes to urinary concentration.

Viktor N Tomilin,Oleg Zaika,Oleh Pochynyuk,Sean P Marrelli,Guohui Ren,Mykola Mamenko,Lutz Birnbaumer,Alexander G Obukhov

doi:10.1371/journal.pone.0226381

Abstract

It is well-established that the kidney collecting duct (CD) plays a central role in regulation of systemic water homeostasis. Aquaporin 2 (AQP2)-dependent water reabsorption in the CD critically depends on the arginine vasopressin (AVP) antidiuretic input and the presence of a favorable osmotic gradient at the apical plasma membrane with tubular lumen being hypotonic compared to the cytosol. This osmotic difference creates a mechanical force leading to an increase in [Ca2+]i in CD cells. The significance of the osmosensitive [Ca2+]i signaling for renal water transport and urinary concentration remain unknown. To examine molecular mechanism and physiological relevance of osmosensitivity in the CD, we implemented simultaneous direct measurements of [Ca2+]i dynamics and the rate of cell swelling as a readout of the AQP2-dependent water reabsorption in freshly isolated split-opened CDs of wild type and genetically manipulated animals and combined this with immunofluorescent detection of AVP-induced AQP2 trafficking and assessment of systemic water balance. We identified the critical role of the Ca2+-permeable TRPC3 channel in osmosensitivity and water permeability in the CD. We further demonstrated that TRPC3 -/- mice exhibit impaired urinary concentration, larger urinary volume and a greater weight loss in response to water deprivation despite increased AVP levels and AQP2 abundance. TRPC3 deletion interfered with AQP2 translocation to the plasma membrane in response to water deprivation. In summary, we provide compelling multicomponent evidence in support of a critical contribution of TRPC3 in the CD for osmosensitivity and renal water handling.

Highlights

Kidneys play a central role in systemic water balance by excreting urine with a highly variable osmolarity depending on hydration status [1, 2]
We and others demonstrated that the mechanosensitive Ca2+-permeable TRPV4 channel is essential for elevations in [Ca2+]i in response to high flow over the apical plasma membrane in the collecting duct (CD) cells [17, 18, 38, 39]
Based on the results of this study, we propose a model where TRPC3 serves as a convergent point between osmosensitive [Ca2+]i signaling and aquaporin 2 (AQP2)-water transport in the CD to regulate renal water handling (Fig 8)

Summary

Introduction

Kidneys play a central role in systemic water balance by excreting urine with a highly variable osmolarity depending on hydration status [1, 2]. AVP stimulation primes the CD to reabsorb water, but this occurs only when positive osmotic difference exists between the cytosol and tubular fluid. This osmotic gradient exerts a mechanical stress of the apical membrane thereby leading to increased cell volume (swelling) and elevated [Ca2+]i [11]. TRP channel activation drives Ca2+ entry from the extracellular medium leading to the elevation of [Ca2+]i to initiate cellular responses [14, 15]. TRPV4 -/- mice do not demonstrate measurable defects in the renal water handling [20, 21] indicating that distinct molecular mechanisms are involved in sensing changes in flow and osmolarity in the CD

Methods

Results

Conclusion