Continuous hypothalamic KATP activation blunts glucose counter-regulation in vivo in rats and suppresses KATP conductance in vitro

Aims/hypothesis

Acute systemic delivery of the sulfonylurea receptor (SUR)-1-specific ATP-sensitive K⁺ channel (K_ATP) opener, NN414, has been reported to amplify glucose counter-regulatory responses (CRRs) in rats exposed to hypoglycaemia. Thus, we determined whether continuous NN414 could prevent hypoglycaemia-induced defective counter-regulation.

Methods

Chronically catheterised male Sprague–Dawley rats received a continuous infusion of NN414 into the third ventricle for 8 days after implantation of osmotic minipumps. Counter-regulation was examined by hyperinsulinaemic–hypoglycaemic clamp on day 8 after three episodes of insulin-induced hypoglycaemia (recurrent hypoglycaemia [RH]) on days 5, 6 and 7. In a subset of rats exposed to RH, NN414 infusion was terminated on day 7 to wash out NN414 before examination of counter-regulation on day 8. To determine whether continuous NN414 exposure altered K_ATP function, we used the hypothalamic glucose-sensing GT1-7 cell line, which expresses the SUR-1-containing K_ATP channel.

Results

Continuous exposure to NN414 in the setting of RH increased, rather than decreased, the glucose infusion rate (GIR), as exemplified by attenuated adrenaline (epinephrine) secretion. Termination of NN414 on day 7 with subsequent washout for 24 h partially diminished the GIR. The same duration of exposure of GT1-7 cells to NN414 substantially reduced K_ATP conductance, which was also reversed on washout of the agonist. The suppression of K_ATP current was not associated with reduced channel subunit mRNA or protein levels.

Conclusions/interpretation

These data indicate that continuous K_ATP activation results in suppressed CRRs to hypoglycaemia in vivo, which in vitro is associated with the reversible conversion of K_ATP into a stable inactive state.