Nitric Oxide Modulates HCN Channels in Magnocellular Neurons of the Supraoptic Nucleus of Rats by an S-Nitrosylation-Dependent Mechanism.
The control of the excitability in magnocellular neurosecretory cells (MNCs) of the supraoptic nucleus has been attributed mainly to synaptic inputs from circunventricular organs. However, nitric oxide (NO), a gaseous messenger produced in this nucleus during isotonic and short-term hypertonic conditions, is an example of a modulator that can act directly on MNCs to modulate their firing rate. NO inhibits the electrical excitability of MNCs, leading to a decrease in the release of vasopressin and oxytocin. Although the effects of NO on MNCs are well established, the mechanism by which this gas produces its effect is, so far, unknown. Because NO acts independently of synaptic inputs, we hypothesized that ion channels present in MNCs are the targets of NO. To investigate this hypothesis, we used the patch-clamp technique in vitro and in situ to measure currents carried by hyperpolarization-activated and nucleotide-gated cation (HCN) channels and establish their role in determining the electrical excitability of MNCs in rats. Our results show that blockade of HCN channels by ZD7288 decreases MNC firing rate with significant consequences on the release of OT and VP, measured by radioimmunoassay. NO induced a significant reduction in HCN currents by binding to cysteine residues and forming S-nitrosothiol complexes. These findings shed new light on the mechanisms that control the electrical excitability of MNCs via the nitrergic system and strengthen the importance of HCN channels in the control of hydroelectrolyte homeostasis.



Cells in our organism live in a liquid environment whose composition and osmolality are maintained within tight limits. Magnocellular neurons (MNCs) of the supra optic nucleus can sense osmolality and control the synthesis and secretion of vasopressin (VP) and oxytocin (OT) by the neurohypophysis. OT and VP act on the kidneys controlling the excretion of water and sodium to maintain homeostasis. Here we combined electrophysiology, molecular biology, and radioimmunoassay to show that the electrical activity of MNCs can be controlled by nitric oxide (NO), a gaseous messenger. NO reacts with cysteine residues (S-nitrosylation) on hyperpolarization-activated and nucleotide-gated cation channels decreasing the firing rate of MNCs and the consequent secretion of VP and OT.
Department of Physiology, Ribeirão Preto Medical School, University of São Paulo, 14049-900 Ribeirão Preto, São Paulo, Brazil, and melina@rfi.fmrp.usp.br.
Melina
0000-0001-5730-0993
M
Pires da Silva
Department of Physiology, Ribeirão Preto Medical School, University of São Paulo, 14049-900 Ribeirão Preto, São Paulo, Brazil, and.
Davi José
DJ
de Almeida Moraes
Department of Physiological Sciences, Biology Institute, Federal Rural University of Rio de Janeiro, 23890-000, Seropédica, Rio de Janeiro, Brazil.
André de Souza
AS
Mecawi
Department of Physiology, Ribeirão Preto Medical School, University of São Paulo, 14049-900 Ribeirão Preto, São Paulo, Brazil, and.
José Antunes
JA
Rodrigues
Department of Physiology, Ribeirão Preto Medical School, University of São Paulo, 14049-900 Ribeirão Preto, São Paulo, Brazil, and.
Wamberto Antonio
0000-0003-3473-3299
WA
Varanda
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002478:Cells, Cultured; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels / Q000378:metabolism*; D015640:Ion Channel Gating / Q000502:physiology*; D008297:Male; D055099:Neuroendocrine Cells / Q000502:physiology*; D009569:Nitric Oxide / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013495:Supraoptic Nucleus / Q000502:physiology*
D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D009569:Nitric Oxide
HCN channels; S-nitrosylation; electrolyte homeostasis; electrophysiology; magnocellular neurons; nitric oxide