title: TRPV4 and K(Ca) ion channels functionally couple as osmosensors in the paraventricular nucleus.
abstract: OBJECTIVE
  Transient receptor potential vanilloid type 4 (TRPV4) and calcium-activated potassium channels (KCa ) mediate osmosensing in many tissues. Both TRPV4 and KCa channels are found in the paraventricular nucleus (PVN) of the hypothalamus, an area critical for sympathetic control of cardiovascular and renal function. Here, we have investigated whether TRPV4 channels functionally couple to KCa channels to mediate osmosensing in PVN parvocellular neurones and have characterized, pharmacologically, the subtype of KCa channel involved.
  
  
  METHODS
  We investigated osmosensing roles for TRPV4 and KCa channels in parvocellular PVN neurones using cell-attached and whole-cell electrophysiology in mouse brain slices and rat isolated PVN neurons. Intracellular Ca(2+) was recorded using Fura-2AM. The system was modelled in the NEURON simulation environment.
  
  
  RESULTS
  Hypotonic saline reduced action current frequency in hypothalamic slices; a response mimicked by TRPV4 channel agonists 4αPDD (1 μM) and GSK1016790A (100 nM), and blocked by inhibitors of either TRPV4 channels (RN1734 (5 μM) and HC067047 (300 nM) or the low-conductance calcium-activated potassium (SK) channel (UCL-1684 30 nM); iberiotoxin and TRAM-34 had no effect. Our model was compatible with coupling between TRPV4 and KCa channels, predicting the presence of positive and negative feedback loops. These predictions were verified using isolated PVN neurons. Both hypotonic challenge and 4αPDD increased intracellular Ca(2+) and UCL-1684 reduced the action of hypotonic challenge.
  
  
  CONCLUSIONS
  There was functional coupling between TRPV4 and SK channels in parvocellular neurones. This mechanism contributes to osmosensing in the PVN and may provide a novel pharmacological target for the cardiovascular or renal systems.
authors.affiliation: Institute of Ageing and Chronic Disease, Faculty of Health & Life Sciences, University of Liverpool, Liverpool, L69 3GA, UK.
authors.forename: C H
authors.initials: CH
authors.lastname: Feetham
authors.forename: N
authors.initials: N
authors.lastname: Nunn
authors.forename: R
authors.initials: R
authors.lastname: Lewis
authors.forename: C
authors.initials: C
authors.lastname: Dart
authors.forename: R
authors.initials: R
authors.lastname: Barrett-Jolley
mesh_terms: D000818:Animals; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008954:Models, Biological; D009474:Neurons / Q000502:physiology; D010286:Paraventricular Hypothalamic Nucleus / Q000502:physiology*; D024681:Potassium Channels, Calcium-Activated / Q000502:physiology*; D017208:Rats, Wistar; D050916:TRPV Cation Channels / Q000502:physiology*
chemical_list: D024681:Potassium Channels, Calcium-Activated; D050916:TRPV Cation Channels; C486576:Trpv4 protein, mouse; C486577:Trpv4 protein, rat