Incubation of NTS Neurons in High Glucose Decreases the Sensitivity to a Low Glucose Challenge: Role of KATP Channels

Abstract

The brainstem nucleus of the tractus solitarius (NTS) is an integrative center for the counterregulatory responses to hypoglycemia, and recent evidences have showed that NTS neurons can directly sense extracellular glucose fluctuations via mechanisms that rely on glucose metabolism. The ATP‐sensitive potassium (KATP) channels play a key role in linking metabolic status and electrical excitability in glucose‐sensing neurons, and KATP channels are expressed in NTS neurons. Therefore, this work aimed to investigate the effect of a low external glucose (0.5 mM) on the membrane properties of NTS neurons of rats, and its interaction with KATP channels, by whole‐cell patch‐clamp. We observed that low glucose induces a voltage‐dependent depolarization in most NTS neurons, i.e., the more negative the resting membrane potential (RMP) of neurons, the higher membrane potential amplitude response. KATP channels are opened at rest in NTS neurons maintained in 5 mM extracellular glucose, and contribute to the hyperpolarized RMP of neurons. Blockage of KATP channels with tolbutamide strongly depolarizes neurons and occludes the effect of low glucose, thus acting as modulators of low‐glucose sensing in NTS neurons. Membrane hyperpolarization after blockage of KATP channels restores the depolarizing effect of low glucose. Additionally, the incubation of NTS neurons in high‐glucose (10 mM) aCSF prior to electrophysiological recordings leads to more depolarized RMP, what contributes to increase the number of neurons unresponsive to a low‐glucose challenge. Again, membrane hyperpolarization restores the depolarization induced by low glucose, however, tolbutamide application did not produced the pronounced membrane depolarization in comparison to NTS neurons incubated in 5 mM glucose aCSF, confirming that KATP channels are closed in a high‐glucose environment. We conclude that (1) low‐glucose sensing in NTS neurons is a voltage‐dependent mechanism; (2) KATP channels influence the RMP of neurons, thus modulating the sensitivity of these neurons to low glucose; (3) incubation of NTS neurons in high‐glucose decrease the number of responsive neurons to low glucose, possibly by depolarization via inhibition of KATP channels following increased amounts of high glucose‐derived ATP levels; (4) this effect could be a permissive mechanism for the decreased brain response to hypoglycemia in individuals that experience recurrent episodes of hypoglycemia, such as insulin‐treated diabetic patients, and; (5) depolarization induced by low glucose might represent a form of homeostatic regulation of the RMP in order to avoid an excessive hyperpolarization by unblocking KATP channels under a hypoglycemia episode.Support or Funding InformationCAPES, CNPq, FAEPA, and FAPESP.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.