Cultured Rat Hippocampal Nerve Cell Membrane Potential Changes On The Action Potential

Fluctuations of membrane potential states are essential for brain functions from the response of individual neurons to the cognitive function of the brain. It has been reported that the duration of action potential is affected by the neuronal membrane potential state in brain slice preparation. However, it is not known whether the membrane potential state dependence of action potential duration also happens at single neuron level, and what is the cellular mechanism for the dependence. By applying patch clamp technique, we found that the action potential duration in cultured hippocampal neurons was dependent on membrane potential state, from which the action potentials were generated. Action potentials generated from relatively depolarized membrane potentials had broader durations than that generated from relatively hyperpolarized membrane potentials, which could conclude that the fluctuation of membrane potential has obvious effect on action potential. Holding membrane potential dependence of outward potassium currents could account for this membrane potential dependence of the action potential duration.This study found that both outward rectifier IK and transient IA currents evoked from relatively depolarized holding membrane potentials had larger magnitude than that generated from relatively hyperpolarized holding membrane potentials. Furthermore, the membrane potential dependence of the action potential duration was significantly reduced in the presence of both TEA and 4-AP, and much less in the presence of 4-AP comparing to that with TEA. Thus, both I_K and IA currents were involved but I_A contributed more in the membrane potential dependence of the action potential duration. These results suggest that through the regulation of voltage-dependent potassium channels, a relatively depolarization potential state, which may be generated from the barrages of input synapses, could play an important role in broadening the action potential duration and consequently modulating the excitability of hippocampal neurons.