Dynamic Control of Presynaptic Ca(2+) Inflow by Fast-Inactivating K(+) Channels in Hippocampal Mossy Fiber Boutons

Neuron. 2000 Dec;28(3):927-39. doi: 10.1016/s0896-6273(00)00164-1.

Abstract

Analysis of presynaptic determinants of synaptic strength has been difficult at cortical synapses, mainly due to the lack of direct access to presynaptic elements. Here we report patch-clamp recordings from mossy fiber boutons (MFBs) in rat hippocampal slices. The presynaptic action potential is very short during low-frequency stimulation but is prolonged up to 3-fold during high-frequency stimulation. Voltage-gated K(+) channels in MFBs inactivate rapidly but recover from inactivation very slowly, suggesting that cumulative K(+) channel inactivation mediates activity-dependent spike broadening. Prolongation of the presynaptic voltage waveform leads to an increase in the number of Ca(2+) ions entering the terminal per action potential and to a consecutive potentiation of evoked excitatory postsynaptic currents at MFB-CA3 pyramidal cell synapses. Thus, inactivation of presynaptic K(+) channels contributes to the control of efficacy of a glutamatergic synapse in the cortex.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials / drug effects
  • Action Potentials / physiology
  • Animals
  • Calcium / metabolism*
  • Elapid Venoms / pharmacology
  • Electric Stimulation / methods
  • Excitatory Postsynaptic Potentials / drug effects
  • Excitatory Postsynaptic Potentials / physiology
  • Glutamic Acid / metabolism
  • In Vitro Techniques
  • Ion Channel Gating / drug effects
  • Ion Channel Gating / physiology
  • Mossy Fibers, Hippocampal / metabolism*
  • Patch-Clamp Techniques
  • Potassium Channel Blockers
  • Potassium Channels / metabolism*
  • Presynaptic Terminals / drug effects
  • Presynaptic Terminals / metabolism*
  • Rats
  • Rats, Wistar
  • Reaction Time / physiology
  • Synaptic Transmission / drug effects
  • Synaptic Transmission / physiology
  • Tetraethylammonium / pharmacology
  • Tetrodotoxin / pharmacology

Substances

  • Elapid Venoms
  • Potassium Channel Blockers
  • Potassium Channels
  • Glutamic Acid
  • Tetrodotoxin
  • Tetraethylammonium
  • dendrotoxin
  • Calcium