Mechanisms For AMPA Receptor Acting On The Secretion Of Pancreatic ? Cell

The insulin secretion in pancreatic?cells is controlled by precise but complex mechanisms, which is the major research focus in pancreatic endocriology. The interactions among islet themselves, different cell types in islets, hormones and cells are entangled but highly ordered. Increased blood sugar levels can increase the cytosolic ATP level and modulate the ATP dependent potassium channel (KATP) activities in?cells. The increase of cytosolic ATP can inhibit KATP conductance, while the increase of ADP reverses the effects of the former. The inactivation of KATP channels caused by high glucose depolarizes?cells and leads to enhanced intracellular calcium and its-dependent activation of cAMP, which finally induces the exocytosis of insulin-containing vesicles.Many metabolic molecules are involved in the regulation of insulin secretion, including neurotransmitters and mitochondria. Pancreatic islets are innervated with many sympathetic and non-sympathetic nerves, sensory and non-cholinergic excitatory neurons, which secrease varied neurotransmitters and regulate the hormone secretion within islets. It is well-known that glutamate receptors are the most important excitatory neurotransmitter receptors in the central nervous system. AMPA receptors are composed of different subunits, GluRl, GluR2, GluR3 and GluR4, in a heterotetramer organization and interact with many intracellular signals. Increasing evidence demonstrate that AMPA receptors are expressed in insulin tumor cells and islets. Glutamate in islets may be secreted from islet a cells and glutamatergic neurons, suggesting that glutamate receptors might be involved in insulin release. However, their roles and mechanisms keep are unknown.Using different techniques, for example, pancreatic slice eletrophysiological recording and live cell imaging, we had investigated the functions of AMPA receptors in islet?cells. We demonstrated that GluR2 subunit-containing AMPA receptors are expressed in mice?cells with whole-cell recordings and nested RT-PCR detections. The activation of AMPA receptors increased both the cytosolic calcium and the docking of insulin-containing granules, which in turn resulted in augmentation of the depolarization-induced exocytosis and the level of insulin release in high glucose condition. These effects were mediated by ATP-sensitive potassium (KATP) channels because glutamate application reduced the conductance of KATP channels and increased their-mediated voltage oscillations. As the result, the actions of AMPA receptors on exocytosis and insulin release were complete blocked in Kir6.2 knock-out mice. Finally, we found that glutamate singling was regulated by the GluR2 interacting protein, PICK1, which inhibited AMPARs'modulation on voltage oscillation and exocytosis.Taken together, our findings are outlined as the followings:1. first recording of functional AMPA currents in?cells in physiological condition; 2. first determination that AMPA receptor currents are important to beta cell exocytosis in?cells; 3. first desmonstration that AMPA receptors affect the sensitivity of KATP channels and low down their conductance in?cells; 4. providing the first evidence that PICK1 protein is able to decrease AMPA receptor-mediated augmentation of exocytosis in?cells; 5. first direct observation that AMPA receptors affect the docking and release of insulin-containing granules by using TIRF. Our results uncover a novel mechanism by which AMPA receptors influence the anchoring of insulin-containing granules and?cell exocytosis. These results help us to better understand the modulatory mechanisms of?cell secretion and might provide an important cue for the therapeutic strategies in insulin disorder diseases.