Epileptiform activity induced by changes in extracellular potassium in hippocampus

Area of Science:

• Neuroscience
• Cellular Electrophysiology

Background:

• Epileptiform activity is a hallmark of epilepsy.
• Extracellular potassium ([K+]o) is known to influence neuronal excitability.

Purpose of the Study:

• To quantitatively investigate the relationship between extracellular potassium concentration and the frequency of spontaneous epileptiform activity.
• To characterize the intracellular mechanisms underlying these epileptiform events.

Main Methods:

• In vitro electrophysiological recordings (intracellular and extracellular) from the CA3 subfield of rat hippocampal slices.
• Application of current- and voltage-clamp techniques.
• Modulation of extracellular potassium ([K+]o) concentration and use of bicuculline.

Main Results:

• A quantitative relationship was established between [K+]o and the frequency of spontaneous epileptiform discharges.
• Increasing [K+]o from 5 to 10 mM resulted in a fivefold increase in discharge rate.
• Spontaneous discharges occurred above 6.5 mM [K+]o, even without bicuculline, at rates faster than bicuculline-induced discharges.
• High-[K+]o-induced discharges were associated with a synaptically mediated paroxysmal depolarizing shift (PDS).

Conclusions:

• Extracellular potassium concentration is a critical determinant of epileptiform discharge frequency.
• The paroxysmal depolarizing shift (PDS) underlying these events is synaptically mediated and influenced by potassium levels.
• These findings provide insights into the mechanisms of epilepsy generation.