Paroxysmal depolarizing shift

A paroxysmal depolarizing shift (PDS) or depolarizing shift is a hallmark of cellular manifestation of epilepsy. Little is known about the initiation, propagation and termination of PDS. Previously, electrophysiological studies have provided the evidence that there is a Ca2+ mediated depolarization, which causes voltage gated Na+ channels to open, resulting in action potentials. This depolarization is followed by a period of hyperpolarization mediated by Ca2+-dependent K+ channels or GABA-activated Cl− influx.. In general, synaptic PDS could be initiated by EPSPs, and the plateau potential of the PDS is maintained by a combination of synaptic potentials (EPSPs, IPSPs) and ionic conductances (persistent sodium current and high-threshold calcium current) and the post-PDS hyperpolarization is governed by multiple potassium currents, activated by calcium or sodium entry, as well as by leak current. The next cycle of depolarization is initiated by both synaptic drive and the hyperpolarization-activated IH current.

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