Distinct mechanisms of [Ca 2+ ] i responses to flow and hypotonicity in the distal nephron (892.5)

Changes in luminal fluid flow or osmolality elicit [Ca 2+ ] i elevations in the distal nephron (DN) cells to regulate water‐electrolyte transport. Our group has recently identified a pivotal role of TRPV4 in mediating flow‐induced Ca 2+ elevations in the DN cells, however little is known about molecular nature of the response to osmotic gradients. Here, using ratiometric Fura‐2 Ca 2+ imaging in freshly isolated split‐opened DNs from wild‐type (WT) mice, we found that hypotonicity elicits a uniform and reproducible increase of [Ca 2+ ] i in DN cells. This response is abolished by removal of extracellular Ca 2+ , but only moderately diminished upon depletion of intracellular Ca 2+ stores. While genetic ablation of TRPV4 abrogates flow‐induced [Ca 2+ ] i elevations, the response to hypotonicity, though significantly blunted, is retained in TRPV4 ‐/‐ mice. This points to additional mechanisms increasing [Ca 2+ ] i in response to osmotic gradients. Indeed, pharmacological inhibition of Ca 2+ ‐permeable TRPC3 channel markedly diminishes the amplitude of [Ca 2+ ] i elevations induced by hypotonic stimuli in DN epithelium from WT mice. Moreover, the threshold of the response to decreased osmolality is elevated in TRPC3 knockouts. Thus, in contrast to flow‐induced [Ca 2+ ] i elevations mediated by TRPV4, hypotonicity elicits a multifaceted Ca 2+ response, at least in part due to coordinated activation of TRPV4 and TRPC3. Grant Funding Source : DK095029