Changes In TRPV4 Channel Function In Vasopressin Neurons Of Rats With Hepatic Cirrhosis

Purpose: Dilutional hyponatremia associated with cardiac and hepatic failure negatively impacts morbidity and mortality of both diseases. Hyponatremia is a consequence of the dysregulation of vasopressin release but is not completely understood. In an animal model of liver failure, the membrane expression of transient receptor potential vanilloid 4 (TRPV4) channels increased in vasopressin-releasing neurons of the hypothalamus. Our hypothesis was that activation of TRPV4 channels with the specific agonist GSK 1019790A produces greater calcium influx in supraoptic nucleus (SON) vasopressin neurons collected from hyponatremic rats with liver failure induced by bile duct ligation surgery or to sham operated controls. Methods: Adult male Sprague-Dawley rats received bile duct ligation surgery or sham ligation surgery. After two weeks, all rats were anesthetized and injected in the SON with an adeno-associated viral 2 (AAV2) vector containing a construct for green fluorescent protein (GFP) driven by a vasopressin-specific promoter. Two weeks later, the rats were anesthetized and the SONs isolated and cultured for Fura-2 ratiometric calcium imaging. Initial experiments had the cultured cells sit overnight prior to imaging; subsequent experiments imaged cells on the same day as their isolation and culturing. SON cells were tested for changes in intracellular calcium produced by the specific TRPV4 agonist GSK 1019790A (20-200 nM). Cells were also tested for its response to a calcium ionophore. In some experiments, data were collected GFP positive (vasopressin) cells. Normalized ratio responses were tested by ANOVA. Results: In these studies using cells cultured for 24-48 hours, 1.5 nM GSK significantly increased calcium influx in GFP-positive cells from sham rats but not from BDL rats (Sham 1.53 ± 0.1, BDL 1.14 ± 0.1, P Conclusion: Our results demonstrate that hyponatremia produces gain in function changes consistent with increased TRPV4 expression. However, these results were strongly influenced by how long the cells were kept in culture.