Chronic exposure to KATPchannel openers results in attenuated glucose sensing in hypothalamic GT1-7 neurons.
Individuals with Type 1 diabetes (T1D) are often exposed to recurrent episodes of hypoglycaemia. This reduces hormonal and behavioural responses that normally counteract low glucose in order to maintain glucose homeostasis, with altered responsiveness of glucose sensing hypothalamic neurons implicated. Although the molecular mechanisms are unknown, pharmacological studies implicate hypothalamic ATP-sensitive potassium channel (KATP) activity, with KATPopeners (KCOs) amplifying, through cell hyperpolarization, the response to hypoglycaemia. Although initial findings, using acute hypothalamic KCO delivery, in rats were promising, chronic exposure to the KCO NN414 worsened the responses to subsequent hypoglycaemic challenge. To investigate this further we used GT1-7 cells to explore how NN414 affected glucose-sensing behaviour, the metabolic response of cells to hypoglycaemia and KATPactivity. GT1-7 cells exposed to 3 or 24 h NN414 exhibited an attenuated hyperpolarization to subsequent hypoglycaemic challenge or NN414, which correlated with diminished KATPactivity. The reduced sensitivity to hypoglycaemia was apparent 24 h after NN414 removal, even though intrinsic KATPactivity recovered. The NN414-modified glucose responsiveness was not associated with adaptations in glucose uptake, metabolism or oxidation. KATPinactivation by NN414 was prevented by the concurrent presence of tolbutamide, which maintains KATPclosure. Single channel recordings indicate that NN414 alters KATPintrinsic gating inducing a stable closed or inactivated state. These data indicate that exposure of hypothalamic glucose sensing cells to chronic NN414 drives a sustained conformational change to KATP, probably by binding to SUR1, that results in loss of channel sensitivity to intrinsic metabolic factors such as MgADP and small molecule agonists.
Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital & Medical School, University of Dundee, Dundee, UK. Electronic address: e.haythorne@imperial.ac.uk.
Elizabeth
E
Haythorne
Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital & Medical School, University of Dundee, Dundee, UK. Electronic address: d.l.hamilton@stir.ac.uk.
D Lee
DL
Hamilton
Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital & Medical School, University of Dundee, Dundee, UK. Electronic address: J.A.Findlay@soton.ac.uk.
John A
JA
Findlay
Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital & Medical School, University of Dundee, Dundee, UK. Electronic address: C.Beall@exeter.ac.uk.
Craig
C
Beall
Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital & Medical School, University of Dundee, Dundee, UK. Electronic address: r.mccrimmon@dundee.ac.uk.
Rory J
RJ
McCrimmon
Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital & Medical School, University of Dundee, Dundee, UK. Electronic address: m.l.j.ashford@dundee.ac.uk.
Michael L J
ML
Ashford
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000493:pharmacokinetics / Q000494:pharmacology*; D002460:Cell Line; D003499:Cyclic S-Oxides / Q000493:pharmacokinetics / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D007003:Hypoglycemia / Q000378:metabolism*; D007031:Hypothalamus / Q000187:drug effects* / Q000378:metabolism; D054086:KATP Channels / Q000819:agonists / Q000378:metabolism*; D051379:Mice; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism
D019086:Bridged Bicyclo Compounds, Heterocyclic; D003499:Cyclic S-Oxides; D054086:KATP Channels; C475618:NN 414; D005947:Glucose
Diazoxide; Diazoxide (PubChem CID: 3019); Glucose sensing; Hypoglycemia; K(ATP); NN414; NN414 (Tifenazoxide) (PubChem CID 219048); Type 1 diabetes