Electrophysiological Mechanism Of Calcium Channel-mediated Pancreatic Islet β Cell Parasecretion In Rat Born Small For Gestational Age

Background Evidence from epidemiological observations suggest that small for gestational age (SGA) tends to the development of metabolic syndrome(MS)/type 2 diabete mellitum(T2DM) in adult life. Intrauterine nutrient limitation occurs in early period when pancreas islet at critical stages of development may induce permanent changes in tissue structure or function. Pancreatic islet beta cell dysfunction is a very important and decisive element that SGA has adult-onset metabolic disease, though the mechanisms are not well understood. Electrical activity and ion channels of theβcell play a central role in stimulus-secretion coupling. Among them, calcium channel whose open and close controls the intracellular Ca2+directly and then regulates insulin release, is the most active ion in pancreaticβcell. Therefore, to study the characteristics of calcium channel and the change of pancreatic isletβcell secretion of SGA will help us to know more about the pathogenesis of pancreatic islet dysfunction happened in SGA. Up to now, there is no paper available about electrophysiological properties ofβcell in SGA.Objective The experiment aimed to investigate whether the effect of intrauterine malnourishment on pancreatic isletβcell will last in postnatal life. Through studying the current and kinetic properties of calcium channel to reveal the mechanism of pancreatic isletβcell secretion variation in SGA rats. From the angle of nutrition, generation and ion channel to research the pathogenesis of pancreatic isletβcell secretion dysfunction in SGA.Methods The animal model of small for gestation in rat was made under matemal calorie restriction by 50% from dl of gestation until term, while the control groups named AGA rats, were obtained from normal pregnant rats. Both of SGA and AGA newborn rats were fed normally till 4 weeks and 8weeks. The animals were killed by cervical dislocation, the abdominal cavity opened and agarose injected into the distally clamped bile duct. The injected and hardened pancreas was then extracted, glued (Super Glue, ND Industries, Troy, Mich., USA) onto plate of the vibrotome (VT 1000 S, Leica, Nussloch, Germany), cut into 130μm-thick. And then the pancreatic slice was kept in an ice-cold extracellular solution bubbled continuously with carbogen to be used. Using whole cell patch clamp to record the characteristics ofβcell voltage dependent calcium channel (such as current, reversal potential, I-V curve, activation curve, inactivation curve) in both SGA and AGA groups at 4 weeks (childhood) and 8weeks (adulthood), respectively. Using capacitance measurement induced by a sequence of sine wave stimulus to reflect the insulin secretion. In a word, study the tendency of calcium channel kinetics and secretion property by timing.Results The membrane capacitance of was smaller than AGA rat after excluding the influence of whole cell membrane capacitance deviation both in 4 weeks and 8 weeks (P<0.05). Also, The membrane capacitance of 8weeks SGA rat was less than 4 weeks SGA rat (P<0.05), while the Cm between 4 weeks and 8weeks AGA rat had no significant difference. Among the calcium channel characteristics, there was no statistical difference found in all average calcium current density (Id), including the total calcium, L-type and T-type. No significant difference was observed in the peak current density of I-V curve in SGA and AGA (P>0.05). However, the reversal potential in SGA group was much lower than control (P<0.05). The two group had the same shape of activation curve and inactivation curve of calcium channel, and 50% activated voltage between SGA and AGA had no significant difference, but the calcium channel of SGA was easily to be closed, the inactivated voltage in SGA group was much higher than control (P<0.01)Conclusion The effect of intrauterine malnourishment on pancreatic isletβcell last in postnatal life and the destroy ofβcell tends to aggravate with time. The current of calcium channel returns to normal level in childhood, however the kinetics of calcium channel is changed significantly. Hence, the change of kinetics may be the reason that intrauterine malnourishment lead to the decrease of insulin secretion in adult life.