Selective transmission of single photon responses by saturation at the rod-to-rod bipolar synapse.
A threshold-like nonlinearity in signal transfer from mouse rod photoreceptors to rod bipolar cells dramatically improves the absolute sensitivity of the rod signals. The work described here reaches three conclusions about the mechanisms generating this nonlinearity. (1) The nonlinearity is caused primarily by saturation of the feedforward rod-to-rod bipolar synapse and not by feedback from horizontal or amacrine cells. This saturation renders the rod bipolar current insensitive to small changes in transmitter release from the rod. (2) Saturation occurs within the G protein cascade that couples receptors to channels in the rod bipolar dendrites, with little or no contribution from presynaptic mechanisms or saturation of the postsynaptic receptors. (3) Between 0.5 and 2 bipolar transduction channels are open in darkness at each synapse, compared to the approximately 30 channels open at the peak of the single photon response.
Sampath
Alapakkam P
AP
Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195, USA.
Rieke
Fred
F
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000596:Amino Acids / Q000494:pharmacology; D000613:Aminobutyrates / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D003624:Darkness; D004347:Drug Interactions; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D066298:In Vitro Techniques; D008027:Light; D008564:Membrane Potentials / Q000187:drug effects / Q000528:radiation effects; D051379:Mice; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D017785:Photons; D012160:Retina / Q000166:cytology*; D017948:Retinal Rod Photoreceptor Cells / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D013569:Synapses / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D014633:Valine / Q000031:analogs & derivatives* / Q000494:pharmacology; D014966:Xanthenes / Q000494:pharmacology
D000596:Amino Acids; D000613:Aminobutyrates; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; C114624:LY 341495; D014966:Xanthenes; C104331:cyclopropyl-4-phosphonophenylglycine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; C056639:2-amino-5-phosphopentanoic acid; C012729:2-amino-4-phosphonobutyric acid; D014633:Valine; D005998:Glycine