title: Reciprocal synaptic interactions between rod bipolar cells and amacrine cells in the rat retina.
abstract: 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.
authors.affiliation: Department of Anatomy and Cell Biology, University of Bergen, N-5009 Bergen, Norway.
authors.forename: E
authors.initials: E
authors.lastname: Hartveit
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000502:physiology; D004594:Electrophysiology; D005071:Evoked Potentials / Q000502:physiology; D005246:Feedback / Q000502:physiology; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D008564:Membrane Potentials / Q000502:physiology; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000502:physiology; D051381:Rats; D018079:Receptors, GABA / Q000502:physiology; D018080:Receptors, GABA-B / Q000502:physiology; D012160:Retina / Q000166:cytology / Q000502:physiology*; D017948:Retinal Rod Photoreceptor Cells / Q000166:cytology / Q000502:physiology*; D015222:Sodium Channels / Q000502:physiology; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000378:metabolism / Q000502:physiology
chemical_list: D015220:Calcium Channels; C087200:GABA-C receptor; D018079:Receptors, GABA; D018080:Receptors, GABA-B; D015222:Sodium Channels; D005680:gamma-Aminobutyric Acid