Reduction of High Glucose-activatedVoltage-Dependent K+ Currents inRat Pancreatic β-cells by KMUP-1

• Main Authors: Han-Jie Tsai, 蔡漢傑
• Other Authors: Bin-Nan Wu
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/62254585901971195872

碩士 === 高雄醫學大學 === 藥理學研究所 === 99 === Pancreatic β-cells release insulin depending on glucose metabolism and membrane depolarization. Insulin secretion is triggered by the closure of ATP-sensitive K+ (KATP) channels, causing a membrane depolarization and Ca2+ influx. Insulin release process is terminated by membrane repolarization via opening of voltage-dependent K+ (Kv) channels. KMUP-1, a chemically synthetic xanthine-based derivative, has been demonstrated not only effective on K+ channels, but also a phosphodiesterases inhibitor. However, it has newer been addressed in the inhibition of Kv channels in pancreatic β-cells. In this study, we examined the action mechanisms by which KMUP-1 could inhibit high glucose (25 mM)-induced Kv current activation in pancreatic β-cells. Pancreatic islets were isolated from Wistar rats. For electrophysiological study, islets were dispersed into single β-cells by 0.05% trypsin-EDTA solution and plated onto 35-mm culture dishes for 2-4 days. Perforated patch-clamp (nystatin 200 μg/mL in pipette solution) technique was used to investigate Kv currents. Pancreatic β-cells were identified by the size, capacitance and membrane potential. The peak Kv current in 25 mM glucose-treated β-cells was ~1.4-fold greater than in 5.6 mM glucose (normal)-treated, measured at +50 mV. KMUP-1 (1, 10, 30 μM) prevented 25 mM glucose-stimulated Kv currents in a concentration-dependent manner. Insulin secretion was decreased after high glucose incubation, and increased by treating KMUP-1. Reduction of high glucose-mediated Kv current was found in incubating protein kinase A (PKA) activator 8-Br-cAMP (100 μM). Additionally, KMUP-1 (30 μM)-inhibited this current was partially reversed by the PKA inhibitor H-89 (1 μM). Otherwise, pretreatment with PKC activator or inhibitor had no effect on Kv currents in normal or high glucose condition. In conclusion, glucose-stimulated insulin secretion was reduced by the Kv channels opening. KMUP-1 could decrease high glucose-stimulated Kv currents via the PKA but not PKC signaling pathway. According to these results, we provide an evidence that KMUP-1 might be useful in the control of type II diabetes.