Pharmacological and molecular characterization of ATP-sensitive K(+) conductances in CART and NPY/AgRP expressing neurons of the hypothalamic arcuate nucleus.
The role of hypothalamic ATP-sensitive potassium channels in the maintenance of energy homeostasis has been extensively explored. However, how these channels are incorporated into the neuronal networks of the arcuate nucleus remains unclear. Whole-cell patch-clamp recordings from rat arcuate nucleus neurons in hypothalamic slice preparations revealed widespread expression of functional ATP-sensitive potassium channels within the nucleus. ATP-sensitive potassium channels were expressed in orexigenic neuropeptide Y/agouti-related protein (NPY/AgRP) and ghrelin-sensitive neurons and in anorexigenic cocaine-and-amphetamine regulated transcript (CART) neurons. In 70% of the arcuate nucleus neurons recorded, exposure to glucose-free bathing medium induced inhibition of electrical excitability, the response being characterized by membrane hyperpolarization, a reduction in neuronal input resistance and a reversal potential consistent with opening of potassium channels. These effects were reversible upon re-introduction of glucose to the bathing medium or upon exposure to the ATP-sensitive potassium channel blockers tolbutamide or glibenclamide. The potassium channel opener diazoxide, but not pinacidil, also induced a tolbutamide and glibenclamide-sensitive inhibition of electrical excitability. Single-cell reverse transcription-polymerase chain reaction revealed expression of mRNA for sulfonylurea receptor 1 but not sulfonylurea receptor 2 subunits of ATP-sensitive potassium channels. Thus, rat arcuate nucleus neurons, including those involved in functionally antagonistic orexigenic and anorexigenic pathways express functional ATP-sensitive potassium channels which include sulfonylurea receptor 1 subunits. These data indicate a crucial role for these ion channels in central sensing of metabolic and energy status. However, further studies are needed to clarify the differential roles of these channels, the organization of signaling pathways that regulate them and how they operate in functionally opposing cell types.