Roles Of Small Conductance Calcium-activated Potassium Channels In Mice With Alzheimer's Disease

Objective:This study was designed to investigate the effects of small conductance calcium-activated potassium (SK) channels on the cognitive function of mice with Alzheimer's disease, and the role of SK channels in apoptosis of hippocampal neurons that induced by Aβ25-35, and analyzed the ImAHP that mediated by SK channels. Thus to explore the role of SK channels in the course of AD.Methods:Animal experiments:according to the ability of swimming and body weight, 60 Kunming female mice were randomly divided into 4 groups:control group, sham-operation group, AD modle group and apamin group. Apamin group was divided into low-dose, mid-dose and high-dose treatment groups. Each group contained 10 mice. AD model group and three apamin groups were given 4μl 1mg/ml Aβ25-35 intracerebroventricular (i.c.v) administration, sham-operation group was treated in the same way with equal-dose saline. After 14 days, Morris water maze test was used to investigate the effects of apamin on cognitive function, and each mouse of apamin group received intraperitoneal apamin respectively 30min before the training trial of each day, and other groups were injected with saline, control group without any treatment, lasted for 5 days. Then immunohistochemistry staining was used to observe the expression of Aβ25-35 among hippocampus CA1 region. Cellular experiments:(1) Mice hippocampal neurons were randomly divided into 3 groups:control group, Aβ25-35 group and apamin group after primary cultured for 8 days. Apamin group was divided into 3 dose group (10nM,100nM and 400nM), each group contained five pores. MTT staining and Hoechst33342 dye were used to assess the viability and apoptosis of hippocampus neurons. (2) Whole-cell patch-clamp techniques were used to observe the variation of ImAHP mediated by SK channels among control, Aβ25-35 group and 100nM apamin group.Results:(1). Compared with control group, the expression of Aβ25-35 in high masculine in hippocampal neurons of AD model group and apamin group. In AD model group, the escape latency was longer, the target quadrant time was shorter, and the number of quadrant entries was fewer(P<0.05), there was no significantly difference between control group and sham-operation group. In apamin groups, compared with AD model group, the escape latency were shorter, the target quadrant time were longer and the number of quadrant entries were more(P<0.05), the expression of Aβ25-35 decreased (P<0.05). All the effects of apamin in a dose-dependent manner. (2). Compared with control group, the viability of hippocampal neurons of Aβ25-35 group significantly decreased, and the apoptosis increased (P<0.05). Compared with Aβ25-35 group, co-incubated with 100nM and 400nM apamin significantly reduced the apoptosis of hippocampal neurons and increased the cell viability in a dose-dependent manner (P<0.05). 10nM group had no significant difference (P>0.05). (3) Compared with control, whole-cell patch-clamp techniques recorded that incubated with Aβ25-35 can increase the amplitude of ImAHP (P<0.05). Compared with Aβ25-35 group, the amplitude of ImAHP of 100nM apamin group decreased significantly (P<0.05).Conclusion:1.Blocked SK channels with its specific blocker apamin, improved the cognitive function of AD mice, reduced the expression of Aβ25-35 at hippocampus CA1 region, and inhibited the apoptosis of hippocampal neurons induced by Aβ25-35.2.Presumed that the mechanism of SK channels in AD might be connected with the variation of ImAHP mediated by SK channels. And SK channels modulated the excitability of neurons and ion homeostasis, reduced the expression of Aβ25-35, thus to protect the neurons.