title: Extracellular calcium and potassium changes in hippocampal slices.
abstract: Ca2+ and K+ ion sensitive microelectrodes were used to measure changes in ionic activities in the CA1 region of hippocampal slices during orthodromic (stratum radiatum) stimulation. Baseline levels of [K+]o and [Ca2+]o were those of the bathing medium which contained 5 mM K+ and 2.0 mM Ca2+. During stimulation [K+]o rose to maximal levels of 12 mM while [Ca2+]o decreased to as low as 1.4 mM. Systematic alterations in extracellular field potentials in stratum pyramidale accompanied the ionic shifts. Following stimulation K+ undershoots occurred. An active K+ uptake mechanism was demonstrated using iontophoretic K+ pulses. [K+]o and [Ca2+]o changes occurred in parallel and in a laminar distribution with maximal changes recorded in stratum pyramidale. Maximal [K+]o changes occurred from baselines of 5 mM and declined progressively at higher baseline levels. During epileptiform activity produced by exposure of slices to penicillin, larger ionic shifts with a more rapid onset occurred. The alterations in [K+]o and [Ca2+]o in the hippocampal slice are similar in some respects to those obtained by stimulation in vivo, making this preparation a potentially useful one for determination of mechanisms and effects of alterations in the ionic microenvironment.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D046508:Culture Techniques; D004558:Electric Stimulation; D006168:Guinea Pigs; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D010400:Penicillin G / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012640:Seizures / Q000139:chemically induced
chemical_list: D007473:Ion Channels; D010400:Penicillin G; D011188:Potassium; D002118:Calcium