Reciprocal synaptic interactions between rod bipolar cells and amacrine cells in the rat retina

J Neurophysiol. 1999 Jun;81(6):2923-36. doi: 10.1152/jn.1999.81.6.2923.


Reciprocal synaptic transmission between rod bipolar cells and presumed A17 amacrine cells was studied by whole cell voltage-clamp recording of rod bipolar cells in a rat retinal slice preparation. Depolarization of a rod bipolar cell evoked two identifiable types of Ca2+ current, a T-type current that activated at about -70 mV and a current with L-type pharmacology that activated at about -50 mV. Depolarization to greater than or equal to -50 mV also evoked an increase in the frequency of postsynaptic currents (PSCs). The PSCs reversed at approximately ECl (the chloride equilibrium potential), followed changes in ECl, and were blocked by gamma-aminobutyric acidA (GABAA) and GABAC receptor antagonists and thus were identified as GABAergic inhibitory PSCs (IPSCs). Bipolar cells with cut axons displayed the T-type current but lacked an L-type current and depolarization-evoked IPSCs. Thus L-type Ca2+ channels are placed strategically at the axon terminals to mediate transmitter release from rod bipolar cells. The IPSCs were blocked by the non-N-methyl-D-aspartate (non-NMDA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione, indicating that non-NMDA receptors mediate the feed-forward bipolar-to-amacrine excitation. The NMDA receptor antagonist 3-((RS)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid had no consistent effect on the depolarization-evoked IPSCs, indicating that activation of NMDA receptors is not essential for the feedforward excitation. Tetrodotoxin (a blocker of voltage-gated Na+ channels) reversibly suppressed the reciprocal response in some cells but not in others, indicating that graded potentials are sufficient for transmitter release from A17 amacrine cells, but suggesting that voltage-gated Na+ channels, under some conditions, can contribute to transmitter release.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium Channels / physiology
  • Electrophysiology
  • Evoked Potentials / physiology
  • Feedback / physiology
  • In Vitro Techniques
  • Ion Channel Gating
  • Membrane Potentials / physiology
  • Patch-Clamp Techniques
  • Presynaptic Terminals / physiology
  • Rats
  • Receptors, GABA / physiology
  • Receptors, GABA-B / physiology
  • Retina / cytology
  • Retina / physiology*
  • Retinal Rod Photoreceptor Cells / cytology
  • Retinal Rod Photoreceptor Cells / physiology*
  • Sodium Channels / physiology
  • Synapses / physiology*
  • Synaptic Transmission / physiology
  • Time Factors
  • gamma-Aminobutyric Acid / metabolism
  • gamma-Aminobutyric Acid / physiology


  • Calcium Channels
  • GABA-C receptor
  • Receptors, GABA
  • Receptors, GABA-B
  • Sodium Channels
  • gamma-Aminobutyric Acid