| Summary: | 碩士 === 高雄醫學大學 === 藥理學研究所 === 100 === Pancreatic β-cells secretion of insulin depends on glucose metabolism and membrane depolarization. High concentration of glucose closes ATP-sensitive K+ channels (KATP channels), causes the membrane depolarization and Ca2+ influx, resulting in insulin secretion.
Eugenosedin-A, a serotonin and α/β receptors blocker, has been reported to prevent hyperglycemia, hyperlipidemia and lipid peroxidation in C57BL/6J mice fed a high-fat diet (HFD). It might be useful in the control of HFD-induced glucose and lipid metabolic disorders. However, its ionic mechanism on pancreatic β cells remains undetermined. In this study, we examined the mechanism by which eugenosedin-A could inhibit KATP channels in rat pancreatic β-cells.
Pancreatic islets were isolated from adult male Wistar rats (250-350 g). For electrophysiology study, islets were dispersed into single β-cells by 0.05% trypsin-EDTA solution and cultured on 35-mm cultured dishes for 2-4 days. Pancreatic β-cells were identified by the cell capacitance, membrane potential and size. Perforated patch-clamp (nystatin 200 μg/mL in pipette solution) technique was used to investigate membrane potential of β-cells. The membrane potential of β-cells was elevated by 3, 10 μM eugenosedin-A and reversed by 100 μM diazoxide. In inside-out patches, 10 μM eugonosedin-A inhibited the KATP channels measured at -60 mV. In fura-2 [Ca2+]i imaging, eugenosedin-A (1, 3, 10 μM)increased pancreatic β-cells [Ca2+]i, but the effects decreased by 100 μM diazoxide. We also used ELISA kit to measure insulin secretion in isolated pancreatic islets, and found 10 μM eugenosedin-A significantly increased insulin secretion.
In in vivo study, diabetic rats were induced by intraperitoneal injection of nicotinamide at 150 mg/kg followed by streptozotocin at a dose of 65 mg/kg after 15 minutes, and their fasting blood glucose levels which exceeded 200 mg/dL one week later were considered as diabetes. Diabetic rats were fed with continuously high fat diets and were divided into three groups：(1) no treatment (2) treated with eugenosedin-A (5 mg/kg, i.p) (3) treated with glibenclamide (0.5 mg/kg, i.p). Fasting blood glucose level of the rats treated with eugenosedin-A for 15 days was decreased below 130 mg/dL.
In conclusion, eugenosedin-A closes KATP channels of pancreatic β-cell, causes membrane potential depolarization, and stimulates Ca2+ influx, resulting in the increase of insulin secretion. It also decreases the blood sugar level of type II diabetic rats. According to these results, we suggest that eugenosedin-A might have benefits for the control of type-II diabetic rats.
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