The Effects Of Soluble Amyloid β-Protein(25-35) On Potassium Currents In Rat Hippocampal Slices CA3 Neurons

Objective:Alzheimer'disease (AD) is a common nervous system disease caused by the chronic progressive degeneration of the brain in the Elderly. At present, exact cause of AD is not elucidate. Most studies showed that the increase of the P-amyloid protein (Aβ) played a central role in the pathogenesis of AD, and insoluble Aβin the brain had specific neurotoxicity. In the early stage of AD, a mass of Aβaccumulated in hippocampus and entorhinal area, aggravating neuronfibrillary tangles and causing a serious of cascades, and eventually leading to cell death. This is the main reason for AD formation. However, other studies indicated that in the early stage of AD, before AP accumulation and neurons apoptosis, soluble oligomers of AP could cause memory impairment, but the mechanism was still unknown. Research found that both central, nervous system and peripheral tissues of AD patients had potassium channels dysfunction. The hippocampus was closely related to learning and memory. The hippocampal cell membrane has a variety of potassium channels, which played an important role on adjusting excitabilities of presynaptic membrane and postsynaptic membrane, and the changes of potassium channels activity and expression influenced its functions. Hippocampal CA3 area correlates closely to learning and memory of spatial discrimination. It is analysed that Aβand Aβ-induced cascades may have direct and/or indirect effects on activity and expression of potassium channels, and the mechanism needs further verified.The effects of soluble Aβ25-35 on potassium currents in CA3 area neurons of neonatal rat hippocampal slices were explored. The effects of soluble Aβ25-35 on peak and kinetics curves of transient outward potassium currents (IA) and delayed rectifier potassium currents (IK) before and after adding soluble Aβ25-35 of different doses in different times were observed, exploring neurontoxic mechanism of soluble Aβ25-35 and providing an experimental support for further revealing pathogenesis of AD and the study on preventive and therapeutic drugs in the early stage of AD.Methods: About 10 to 11 days Wistar rats were rapidly decapitated. The hippocampus transverse slices (thickness 350μm) were cut. The slice patch clamp whole-cell recording technique was used to record the peak and waveform of IA and IK in CA3 area neurons of neonatal rat hippocampal slices before and after adding soluble AP25-35 of different doses in different times, tracing current-voltage curve and kinetic curves. The kinetic characters of IA and IK were analyzed using Igor5.01 and Origin7.5 software.Results:1. Before adding soluble AP25-35, IA in CA3 area neurons of neonatal rat hippocampal slices were 1346.67±95.70,1256.67±60.64 and 2200.00±198.39nA(n=7), respectively. After adding 1.0,2.5,5.0μmol/L soluble AP25-35, IA decreased in a time-dependent manner. IA were 708.67±76.39,581.67±36.40 and 864.25±118.01nA,25min after adding soluble A(325-35.The inhibition rates were 45.65±5.36,53.11±6.73 and 61.28±4.39%, respectively. There was a significant difference between control group and drug group (P<0.01). There was a significant difference among drug groups (F=13.29, P<0.05). Compared to the control group, IAⅠ-Ⅴcurve descended with depolarization after adding soluble Aβ25-35. IA activation and inactivation kinetic curves moved to more negative potentials in a dose-dependent manner.2. Before adding soluble Aβ5-35, IK in CA3 area neurons of neonatal rat hippocampal slices were 1314.44±57.29,1301.85±38.16 and 1095.00±25.34nA(n=8), respectively. After adding 1.0,2.5,5.0μmol/L soluble Aβ25-35, IK decreased in a time-dependent manner. IK were 592.00±30.07,528.00±40.00 and 418.00±50.10nA,27min after adding soluble Aβ25-35. The inhibition rates were 57.52±1.94,60.55±3.58 and 62.04±5.04%, respectively. There was a significant difference between control group and drug group (P<0.01), but no significant difference among drug groups (F=0.64, P>0.05). Compared to the control group, IKⅠ-Ⅴcurve descended with depolarization after adding soluble Aβ25-35. IK activation kinetic curves moved to more negative potentials in a dose-dependent manner Conclusions:1. Soluble Aβ25-35 obviously inhibited IA in CA3 neurons of rat hippocampal slices in time-dependent, concentration-dependent and voltage-dependent manners in a certain range. Soluble AP25-35 significantly shifted the activation and inactivation curves of IA to more negative potentials in a dose-dependent manner.2. Soluble Aβ25-35 obviously inhibited IK in CA3 neurons of rat hippocampal slices in time-dependent and voltage-dependent in a certain range. But the inhibition effect was not significant difference in a dose-dependent in 1.0-5.0μmol/L. Soluble Aβ25-35 significantly shifted the activation curves of IK to more negative potentials in a dose-dependent manner.3. The inhibition effects of soluble Aβ25-35 on IA and IK may be one of neurotoxic mechanisms. It involved directly and indirectly in the pathogenesis of AD and played an important role in the presence of early symptoms of AD.