Abstract
The unsaturated fatty acid, oleate exhibits anorexigenic properties reducing food intake and hepatic glucose output. However, its mechanism of action in the hypothalamus has not been fully determined. This study investigated the effects of oleate and glucose on GT1-7 mouse hypothalamic cells (a model of glucose-excited (GE) neurons) and mouse arcuate nucleus (ARC) neurons. Whole-cell and perforated patch-clamp recordings, immunoblotting and cell energy status measures were used to investigate oleate- and glucose-sensing properties of mouse hypothalamic neurons. Oleate or lowered glucose concentration caused hyperpolarization and inhibition of firing of GT1-7 cells by the activation of ATP-sensitive K+ channels (KATP). This effect of oleate was not dependent on fatty acid oxidation or raised AMP-activated protein kinase activity or prevented by the presence of the UCP2 inhibitor genipin. Oleate did not alter intracellular calcium, indicating that CD36/fatty acid translocase may not play a role. However, oleate activation of KATP may require ATP metabolism. The short-chain fatty acid octanoate was unable to replicate the actions of oleate on GT1-7 cells. Although oleate decreased GT1-7 cell mitochondrial membrane potential there was no change in total cellular ATP or ATP/ADP ratios. Perforated patch and whole-cell recordings from mouse hypothalamic slices demonstrated that oleate hyperpolarized a subpopulation of ARC GE neurons by KATP activation. Additionally, in a separate small population of ARC neurons, oleate application or lowered glucose concentration caused membrane depolarization. In conclusion, oleate induces KATP-dependent hyperpolarization and inhibition of firing of a subgroup of GE hypothalamic neurons without altering cellular energy charge.
Highlights
The hypothalamus is critical for the continuous regulation of whole-body glucose, lipid and energy homeostasis
We have previously demonstrated that this neuronal cell line shows graded electrical responses over a physiological range of glucose concentrations and that these responses can be modulated by pharmacological manipulation of the classical components of glucosesensing, namely glucokinase, adenosine 50-monopho sphate-activated protein kinase (AMPK) and KATP (Beall et al, 2012)
As AMPK has been implicated as a key component of cellular glucose sensing in hypothalamic neurons (Claret et al, 2007), GT1-7 neurons (Beall et al, 2012) and pancreatic beta cells (Beall et al, 2010), we examined whether oleate alters AMPK activity
Summary
The hypothalamus is critical for the continuous regulation of whole-body glucose, lipid and energy homeostasis To perform this function, various hypothalamic nuclei (e.g. arcuate (ARC), ventromedial (VMN), lateral hypothalamic area and paraventricular) contain neuropeptide-expressing neurons that monitor circulating nutrients and hormone levels (Levin et al, 2004). GE neurons utilize ATP-sensitive potassium (KATP) channels (in a manner similar to pancreatic beta cells (MacDonald et al, 2005) to modulate their electrical activity in response to changes in extracellular glucose concentration (Ashford et al, 1990; Wang et al, 2004; Kang et al, 2006). In order to explore the mechanisms by which oleate modifies neuronal excitability we have examined the interplay between nutrient-dependent pathways and oleate responses in mouse GE-type neurons
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