Prolonged exposure to high potassium concentration results in irreversible loss of synaptic transmission in hippocampal tissue slices.
Since elevation of the concentration of free calcium in the cytoplasm ([Ca2+]i) during hypoxia is believed to cause injury to cells and since during Leão's spreading depression (LD) excess calcium accumulates in neurons, we asked whether LD of prolonged duration in well oxygenated tissue causes irreversible loss of function. LD-like depolarization of controlled duration was induced by irrigating hippocampal tissue slices with a high-K+ solution for varying time periods. Interstitial potassium concentration ([K+]o) and extracellular potentials were recorded. Following brief LD there was a period of transient hyperexcitability with increased orthodromic population spike amplitude and burst firing, followed by recovery to control levels after 60 min. When depolarization was prolonged beyond 4 or 5 min, the hyperexcitable period was followed by severely depressed transmission. The data are compatible with the hypothesis that prolonged elevation of [Ca2+]i causes neuron injury. Exposure of in vitro preparations to high [K+]o cannot be regarded as the equivalent of a physiological stimulus.
Kawasaki
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Department of Physiology, Duke University Medical Center, Durham, NC 27710.
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D000818:Animals; D005071:Evoked Potentials; D005260:Female; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects*
D011188:Potassium