| Glybenclamide,a sulfonylurea receptor 1 blocker,is taken as a clinical drug for the treatment of non-insulin-dependent diabetes mellitus.The voltage-dependent K+(Kv)channel Kv2.1 ubiquitously expressed in a variety of excitable tissues,including the heart and brain,plays a pivotal role in the modulation of electrical activity,tuning action potential repolarization and excitability.In pancreatic islet?-cells,previous reports also showed that Kv2.1 channel contributed to insulin exocytosis evoked by glucose stimulation,mainly due to its action on electrical function of these cells.It's generally believed that glybenclamide exerts its efficacy by blocking ATP-sensitive K+(KATP)channels located in pancreatic?-cells,producing a depolarization to allow Ca2+influx for insulin release.Nevertheless,it is not clear whether this chemical could also affects the electrical properties of Kv2.1 channel heterologously expressed in HEK293 cells.By using a strategy that combines patch clamp recordings with mutagenesis techniques,we found that extracellular exposure to glybenclamide could potently inhibit Kv2.1 currents,with a half maximum inhibitory concentration(IC50)of 0.61?M.Furthermore,the sensitivity in response to addition of glybenclamide in two mutations K356G and Y380R is significantly lower compared with wild-type control,implying that these positions are the binding sites of drug to Kv2.1 channel.Detailed studies indicated that glybenclamide accelerated the deactivation process of Kv2.1channel without changing the activation curve.Additionally,the inactivation curve of wild-type Kv2.1 currents was markedly shifted to more negative potentials by glybenclamide,whereas this effect was substantially released in above mutations K356G and Y380R.The present data provide the direct evidence that the Kv2.1channel abundantly expressed in?-cells of the pancreatic islets is implicated in pharmacological actions of glybenclamide and could be served as a potential therapeutic target for diabetes. |
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