Accumulation and extrusion of permeant Ca2+ chelators in attenuation of synaptic transmission at hippocampal CA1 neurons

Neuroscience. 1996 Nov;75(1):99-109. doi: 10.1016/0306-4522(96)00319-3.


The effects of extracellularly applied membrane-permeant Ca2+ chelators on field excitatory postsynaptic potentials were determined in the hippocampal CA1 region of rat brain slices. Field excitatory postsynaptic potentials in slices perfused with 0.05-50 microM bis-(-O-aminophenoxy)-ethane-N,N,N,N,-tetraacetic acid acetoxymethyl (BAPTA-AM) for 15 min were reversibly attenuated by 10-45% in a concentration-dependent manner. Attenuation occurred earlier at higher concentrations of BAPTA-AM, thus indicating that the rate of accumulation of BAPTA salt was concentration dependent. Antidromically evoked responses and presynaptic volleys were unaffected by BAPTA-AM. Attenuation of the field excitatory postsynaptic potentials by BAPTA-AM was temporarily eliminated by repetitive stimulation at 1 Hz, suggesting saturation of the chelator's Ca(2+)-binding capacity. The amplitude of field excitatory postsynaptic potentials was unaffected by similar applications of 5'5-dinitro-BAPTA-AM, a low Ca(2+)-affinity BAPTA analogue, and EGTA-AM (5 or 50 microM), a chelator with slow Ca(2+)-binding kinetics, suggesting a dependence of the BAPTA-AM effect on fast Ca2+ binding and high Ca2+ affinity. BAPTA-AM concentrations as low as 0.05 microM were effective provided application was prolonged to 40 min. Probenecid (1 mM), an anion transport inhibitor, accelerated the onset and significantly enhanced the BAPTA-mediated synaptic attenuation caused by low concentrations of BAPTA-AM. These data show that even very low extracellular concentrations of BAPTA-AM can profoundly affect synaptic transmission provided that sufficient chelator accumulates presynaptically. The effectiveness of BAPTA-AM can be increased by procedures which inhibit chelator extrusion.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biological Transport / drug effects
  • Calcium / metabolism*
  • Cell Membrane Permeability
  • Chelating Agents / metabolism*
  • Chelating Agents / pharmacology
  • Egtazic Acid / analogs & derivatives
  • Egtazic Acid / pharmacology
  • Hippocampus / cytology*
  • Hippocampus / drug effects
  • Hippocampus / metabolism
  • Kinetics
  • Male
  • Neurons / drug effects
  • Neurons / metabolism*
  • Probenecid / pharmacology
  • Rats
  • Rats, Wistar
  • Synaptic Transmission / drug effects
  • Synaptic Transmission / physiology*


  • 5,5'-dinitro-1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester
  • Chelating Agents
  • 1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester
  • Egtazic Acid
  • EGTA acetoxymethyl ester
  • Probenecid
  • Calcium