title: Neuronal sodium leak channel is responsible for the detection of sodium in the rat median preoptic nucleus.
abstract: Sodium (Na(+)) ions are of primary importance for hydromineral and cardiovascular homeostasis, and the level of Na(+) in the body fluid compartments [plasma and cerebrospinal fluid (CSF)] is precisely monitored in the hypothalamus. Glial cells seem to play a critical role in the mechanism of Na(+) detection. However, the precise role of neurons in the detection of extracellular Na(+) concentration ([Na(+)](out)) remains unclear. Here we demonstrate that neurons of the median preoptic nucleus (MnPO), a structure in close contact with the CSF, are specific Na(+) sensors. Electrophysiological recordings were performed on dissociated rat MnPO neurons under isotonic [Na(+)] (100 mM NaCl) with local application of hypernatriuric (150, 180 mM NaCl) or hyponatriuric (50 mM NaCl) external solution. The hyper- and hyponatriuric conditions triggered an in- and an outward current, respectively. The reversal potential of the current matched the equilibrium potential of Na(+), indicating that a change in [Na(+)](out) modified the influx of Na(+) in the MnPO neurons. The conductance of the Na(+) current was not affected by either the membrane potential or the [Na(+)](out). Moreover, the channel was highly selective for lithium over guanidinium. Together, these data identified the channel as a Na(+) leak channel. A high correlation between the electrophysiological recordings and immunofluorescent labeling for the Na(X) channel in dissociated MnPO neurons strongly supports this channel as a candidate for the Na(+) leak channel responsible for the Na(+)-sensing ability of rat MnPO neurons. The absence of Na(X) labeling and of a specific current evoked by a change in [Na(+)](out) in mouse MnPO neurons suggests species specificity in the hypothalamus structures participating in central Na(+) detection.
authors.affiliation: Centre de Recherche du CHUL, Département de Psychiatrie/Neurosciences, Université Laval, Québec, Canada.
authors.forename: Christina
authors.initials: C
authors.lastname: Tremblay
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Berret
authors.forename: Mélaine
authors.initials: M
authors.lastname: Henry
authors.forename: Benjamin
authors.initials: B
authors.lastname: Nehmé
authors.forename: Louis
authors.initials: L
authors.lastname: Nadeau
authors.forename: Didier
authors.initials: D
authors.lastname: Mouginot
mesh_terms: D000818:Animals; D015640:Ion Channel Gating / Q000502:physiology*; D051379:Mice; D009474:Neurons / Q000502:physiology*; D011301:Preoptic Area / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000502:physiology*; D013045:Species Specificity; D014882:Water-Electrolyte Balance / Q000502:physiology*
chemical_list: D015222:Sodium Channels; D012964:Sodium