| Bisphenol A (BPA) is an environmental endocrine disruptors that is widely used in the baby bottle and food package as a plasticizer. Accumulating data have revealed that BPA exposure at the concentration of permissible exposure limit lead to glucose metabolic disturbance and insulin level abnormality on animals.Diabetes is a major global problem, which severely impairs human health and places a severe economic burden on governments and individuals. Type2diabetes account for more than90%of the diabetes and is characterized by insulin resistance and insufficient insulin secretion. Currently, therapy for type2diabetes relies mainly on reducing the hyperglycemia, and drugs for those related insulin secretagogues are one of the most important approaches. Glucose stimulate insulin release is one of the typical process of stimulus-secretion coupling that involves several ion channel, and ATP sensitive potassium channel (KATP) plays an important role during the depolarization, like sulphonylureas, which is used to treat diabetes for about70years. However, whether the voltage gated potassium channels (Kv) participated in the repolarization during the GSIS remains unknown.Serum insulin lever is closely related to insulin synthesis and release in pancreatic β cell, both of which are regulated by many factors. Of all, blood glucose is the major one during this process. After feeding, increased glucose level results in more glucose transportation into pancreatic β cell by GLUT2, which produces more ATP to affect the cell electrical activities, and finally increases insulin release. In addition, it also activates a series of transcription factors which affect on insulin synthesis. However, whether these channels are involved in BPA-mediated insulin synthesis and release are still unknown.Consequently, in the present study, the role of Kv2.1in the procedure of GSIS and the corresponding mechanisms are explored. We also investgated the effect of low dose bisphenol A on insulin synthesis and release in isolated pancreatic β cell, especially for the membrane transporters and ion channels changes during the procedure.With the whole cell patch clamp assay, we found that Kv2.1is the major contributor in the outward K+currents of pancreatic β cell, and the effect of GxTx-1E on GSIS was observed by RIA. Calcium oscillation was detected by the confocal laser microscopy. Furthermore, the relative mRNA expression was obtained via RT-PCR.The results showed that Kv2.1accounted for80%of Kv current. And GxTx-lE at the concentration of500nmol/L significantly increased insulin release when pancreatic islets were stimulated by16.7mmol/L glucose, but not by3.3mmol/L glucose. Additionally, intracellular calcium oscillation amplitude, frequency were increased when500nmol/L GxTx-lE were treated in the16.7mmol/L glucose buffer.When isolated islets were exposed to low dose BPA (100nmol/L) for24hour, relative mRNA expression of insulin, Cav and Kv2.1increased when compared with control (p<0.05), Glut2mRNA expression was decreased (p<0.05) and KATP has not changed (p>0.05). In addition,10nM BPA could increase insulin release in the condition of16.7nmol/L glucose (p<0.05) rather than in3.3mmol/L glucose (p>0.05). However, BPA did no affect on Kv current even at the concentration of500nmol/L.These results indicate that Kv2.1inhibition results in increasing GSIS in high glucose level which might due to the effects of Kv2.1on the amplitude and frequency of intracellular calcium oscillation. Low dose of BPA increases insulin synthesis which might be associated with many factors, such as Cav channels and Glut2. In addition, BPA affects Cav and Kv2.1mRNA expression, which might regulate insulin release. However, at least in the indicated doses of BPA in our group, BPA showed no obvious effects on Kv channel electrical activity. |
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