Abstract
NMDA receptors (NMDARs) are Ca(2+)-permeant, ligand-gated ion channels activated by the excitatory neurotransmitter glutamate and have well-characterized roles in the nervous system. The expression and function of NMDARs in pancreatic β-cells, by contrast, are poorly understood. Here, we report a novel function of NMDARs in β-cells. Using a combination of biochemistry, electrophysiology, and imaging techniques, we now show that NMDARs have a key role in mediating the effect of leptin to modulate β-cell electrical activity by promoting AMP-activated protein kinase (AMPK)-dependent trafficking of K(ATP) and Kv2.1 channels to the plasma membrane. Blocking NMDAR activity inhibited the ability of leptin to activate AMPK, induce K(ATP) and Kv2.1 channel trafficking, and promote membrane hyperpolarization. Conversely, activation of NMDARs mimicked the effect of leptin, causing Ca(2+) influx, AMPK activation, and increased trafficking of K(ATP) and Kv2.1 channels to the plasma membrane, and triggered membrane hyperpolarization. Moreover, leptin potentiated NMDAR currents and triggered NMDAR-dependent Ca(2+) influx. Importantly, NMDAR-mediated signaling was observed in rat insulinoma 832/13 cells and in human β-cells, indicating that this pathway is conserved across species. The ability of NMDARs to regulate potassium channel surface expression and thus, β-cell excitability provides mechanistic insight into the recently reported insulinotropic effects of NMDAR antagonists and therefore highlights the therapeutic potential of these drugs in managing type 2 diabetes.