Glucose Deprivation Regulates K_ATP Channel Trafficking via AMP-Activated Protein Kinase in Pancreatic β-Cells

Abstract

OBJECTIVE AMP-activated protein kinase (AMPK) and the ATP-sensitive K⁺ (K_ATP) channel are metabolic sensors that become activated during metabolic stress. AMPK is an important regulator of metabolism, whereas the K_ATP channel is a regulator of cellular excitability. Cross talk between these systems is poorly understood.

RESEARCH DESIGN AND METHODS Rat pancreatic β-cells or INS-1 cells were pretreated for 2 h at various concentrations of glucose. Maximum K_ATP conductance (G_max) was monitored by whole-cell measurements after intracellular ATP washout using ATP-free internal solutions. K_ATP channel activity (NPo) was monitored by inside-out patch recordings in the presence of diazoxide. Distributions of K_ATP channel proteins (Kir6.2 and SUR1) were examined using immunofluorescence imaging and surface biotinylation studies. Insulin secretion from rat pancreatic islets was measured using an enzyme immunoassay.

RESULTS G_max and NPo in cells pretreated with glucose-free or 3 mmol/l glucose solutions were significantly higher than in cells pretreated in 11.1 mmol/l glucose solutions. Immunofluorescence imaging and biotinylation studies revealed that glucose deprivation induced an increase in the surface level of Kir6.2 without affecting the total cellular amount. Increases in G_max and the surface level of Kir6.2 were inhibited by compound C, an AMPK inhibitor, and siAMPK transfection. The effects of glucose deprivation on K_ATP channels were mimicked by an AMPK activator. Glucose deprivation reduced insulin secretion, but this response was attenuated by compound C.

CONCLUSIONS K_ATP channel trafficking is regulated by energy status via AMPK, and this mechanism may play a key role in inhibiting insulin secretion under low energy status.