AMPA receptors with high Ca2+ permeability mediate synaptic transmission in the avian auditory pathway

J Physiol. 1995 Jan 15;482 ( Pt 2)(Pt 2):309-15. doi: 10.1113/jphysiol.1995.sp020519.


1. The permeability of AMPA (alpha-amino-3-hydroxy-5-methyl-4- isoxazolepropionate) receptors in the chick cochlear nucleus, the nucleus magnocellularis (nMAG), was examined by measuring the shift in reversal potential (Erev) of current through glutamate or neurotransmitter-gated channels in solutions of different ionic composition. 2. Outwardly rectifying glutamate-activated currents in outside-out membrane patches showed rapid activation and desensitization. The Erev of glutamate-evoked current in zero sodium solutions was dependent on the extracellular Ca2+ concentration. The relation between Erev and Ca2+ ionic activities could be described by the Goldman-Hodgkin-Katz equation with a permeability ratio, PCa/PCs, of 3.3. The PNa/PCs was estimated as 0.66, indicating a PCa/PNa of 5. 3. Evoked excitatory postsynaptic currents (EPSCs) could be recorded during local perfusion of the auditory nerve-nMAG synapse with isotonic Ca2+. The Erev of the EPSC shifted in the positive direction in high-Ca2+ solution as predicted from the preceding analysis. The fraction of current carried by Ca2+ during the AMPA receptor EPSC was estimated as 18%.

Publication types

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

MeSH terms

  • Animals
  • Auditory Pathways / chemistry
  • Auditory Pathways / physiology*
  • Auditory Pathways / ultrastructure
  • Calcium / pharmacokinetics*
  • Calcium Channels / physiology*
  • Cell Membrane Permeability / physiology
  • Chick Embryo
  • Electrophysiology
  • Evoked Potentials, Auditory, Brain Stem
  • Glutamic Acid / pharmacology
  • Kinetics
  • Receptors, AMPA / physiology*
  • Synaptic Transmission / physiology*


  • Calcium Channels
  • Receptors, AMPA
  • Glutamic Acid
  • Calcium