1 Department of Neurology, the Second Affiliated Hospital of Harbin Medical University, 2 Department of Physiology, Harbin Medical University, Harbin 150086, China

Abstract 

Objective 
Concentration of extracellular calcium ([Ca2+]o) in the central nervous system decreases substantially in different conditions. It Results in facilitating neuronal excitability. The goal of this study is to examine the mechanisms of enhanced neuronal excitation in low [Ca2+]o in order to provide new clues to treat the hyperexcitability diseases in clinic. 
Methods 
Whole-cell patch-clamp technique and neuron culture were used in the study. 
Results 
The firing threshold of cultured hippocampal neurons decreased markedly in low [Ca2+]o saline. Unexpectedly, apamine and isoprenaline, antagonists of medium afterhyperpolarization (mAHP) and slow AHP (sAHP) respectively, had no statistic significant effect on excitability of neurons. TTX at a low concentration was sufficient to inhibit I NaP, which blocked the increase of firing frequency in low [Ca2+]o. It also reduced the number of spikes in normal [Ca2+]o. 
Conclusion 
These Results suggest that in cultured hippocampal neurons, modulation of spiking threshold but not AHP may cause the increased excitability in low [Ca2+]o.

Keywords

small-conductance calcium-activated potassium channels (SKCa); hippocampus; calcium

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