Variant firing patterns in rat hippocampal pyramidal cells modulated by extracellular potassium

J Neurophysiol. 1994 Mar;71(3):831-9. doi: 10.1152/jn.1994.71.3.831.


1. The distribution of distinctive firing modes within the population of CA1 pyramidal cells and their modulation by the extracellular concentration of potassium ([K+]o) were investigated with intracellular recordings in rat hippocampal slices. 2. Pyramidal cells were injected with long (> 250 ms) and brief (3-5 ms) positive current pulses of increasing intensity. In normal [K+]o (3.5 mM), most cells (38 of 46 cells; 83%) were regular spiking neurons (generating accommodating trains of independent action potentials during long depolarizations and a single spike in response to brief stimuli). The remaining pyramidal cells (8 of 46; 17%) displayed differential tendencies to generate stereotyped clusters of action potentials, or bursts, according to which they were grouped into three subsets of endogenous bursters: grade I, bursting only when stimulated with long depolarizing current pulses (6 of 46; 13%); grade II, bursting also in response to brief stimulation (1 of 46; 2%); grade III, bursting also spontaneously even in absence of synaptic transmission (1 of 46; 2%). 3. Raising [K+]o from 3.5 to 7.5 mM (high [K+]o) significantly reduced resting membrane potential and input impedance but did not change the threshold potential for eliciting an action potential. 4. Raising [K+]o to 7.5 mM reversibly converted many regular spiking cells to bursters. Likewise, the burst tendency of normally bursting pyramidal cells increased to a higher grade in high [K+]o. Consequently, the fraction of bursters in high [K+]o (17 of 41 cells; 42%) was approximately 2.5-fold higher than in normal [K+]o and their differential distribution was shifted toward higher grades of bursting.(ABSTRACT TRUNCATED AT 250 WORDS)

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Culture Techniques
  • Evoked Potentials / physiology
  • Extracellular Space / physiology*
  • Hippocampus / physiology*
  • Nerve Net / physiology
  • Neurons / physiology
  • Potassium / physiology*
  • Potassium Channels / physiology*
  • Rats
  • Rats, Wistar
  • Synaptic Transmission / physiology*


  • Potassium Channels
  • Potassium