| Background The rapidly increasing prevalence of metabolic syndrome (MS) and type 2 diabetes mellitus (T2DM) is one of the most challenging problems, which has caused serious harm to human health. Small for gestational age (SGA) due to intrauterine malnourishment is closely related to the incidence of MS and T2DM for the high prevalence of these diseases when SGA children through to adulthood. Among the complex and diverse pathogenesis, pancreatic islet dysfunction is a very important element that links SGA with adult metabolic diseases. However, it is unclear how pancreatic islet dysfunction developed in SGA. As known to us, calcium signal is a key regulator in insulin secretion, and calcium influx through high-voltage-activated(HVA) calcium channel is a most important component that leading to the intracellular calcium signal variation. Therefore, to research the characteristics of HVA calcium channel and its relationship with pancreatic isletβcell secretion will help us to learn more deeply the pathogenesis that pancreatic islet dysfunction developed in SGA. Currently, there are no research reports about changes of calcium channel characteristics and its relationship with pancreatic isletβcell secretion in the world.Objective The experiment aimed to investigate the effect of intrauterine malnourishment on pancreatic isletβcell HVA calcium channel characteristics in neonatal rat born SGA. Meanwhile, we are able to find out whetherβcell parasecretion already exist in SGA during their neonatal period, then to reveal the relationship between the changes of HVA calcium channel characteristics and pancreatic isletβcell secretion variation in SGA neonatal rats.Methods SGA neonatal rat model was created by reducing in maternal total food intake to 50%of ad-lib during pregnancy in mother rat. The control groups, namely AGA neonatal rats, were obtained from pregnant rats which were fed ad-lib. The experiment protocol was as follows:Firstly, the neonatal rats (10 pups per group) were killed by decapitation within 24 hours after they were born. Then, their pancreases were extracted under sterile conditions. After that, pancreatic islets and single islet cells were isolated by enzyme digestion followed with islet/cell incubation and identification. After whole night incubation, the pancreatic islet cells were took out of the incubator, and whole cell patch clamp was used to test characteristics ofβcell HVA calcium channel (such as average calcium current density-Id, I-Ⅴcurve, activation curve, inactivation curve) in both group SGA and group AGA. Capacitance variation ofβcells was also recorded after cells being stimulated by giving a sine wave stimulus. Finally, the differences of these parameters between the two groups were compared to reveal the relationship between the changes of HVA calcium channel characteristics and pancreatic isletβcell secretion variation in SGA neonatal rats.Results Compared with group AGA, SGA neonatal rats showed much lower value of the HVA calcium current density (Id) in pancreatic isletβcells (P＜0.05). Among the other calcium channel characteristics of the two groups, peak current density of I-Ⅴcurve in SGA was lower than in AGA (P<0.05), which was perfectly consistent with the result that test from depolarization from-40mV to OmV, but there was no statistical difference found in reversal potential (P>0.05). The same result was obtained in activation curve and inactivation curve of HVA calcium channel, whose half activated voltage/half inactivated voltage V1/2 and slope factor k between SGA and AGA both showed no significant difference (P>0.05). The membrane capacitance increment ofβcells was smaller in SGA rat compared with AGA rat after excluding the influence of whole cell membrane capacitance deviation (P<0.05).Conclusion Low HVA calcium current density onβcell membrane, which may lead to change of calcium signal, play an important role in decrease ofβcell secretion in SGA neonatal rat caused by intrauterine malnourishment. |
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