Light evokes Ca2+ spikes in the axon terminal of a retinal bipolar cell.
Bipolar cells in the vertebrate retina have been characterized as nonspiking interneurons. Using patch-clamp recordings from goldfish retinal slices, we find, however, that the morphologically well-defined Mb1 bipolar cell is capable of generating spikes. Surprisingly, in dark-adapted retina, spikes were reliably evoked by light flashes and had a long (1-2 s) refractory period. In light-adapted retina, most Mb1 cells did not spike. However, an L-type Ca2+ channel agonist could induce periodic spiking in these cells. Spikes were determined to be Ca2+ action potentials triggered at the axon terminal and were abolished by 2-amino-4-phosphonobutyric acid (APB), an agonist that mimics glutamate. Signaling via spikes in a specific class of bipolar cells may serve to accelerate and amplify small photo-receptor signals, thereby securing the synaptic transmission of dim and rapidly changing visual input.
Protti
D A
DA
Max-Planck Institute for Biophysical Chemistry, Göttingen, Germany. protti@mpih-frankfurt.mpg.de
Flores-Herr
N
N
von Gersdorff
H
H
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000221:Adaptation, Ocular / Q000502:physiology; D000613:Aminobutyrates / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000502:physiology; D002450:Cell Communication / Q000502:physiology; D003623:Dark Adaptation / Q000502:physiology; D017097:Electric Impedance; D004594:Electrophysiology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D006054:Goldfish; D009543:Nifedipine / Q000494:pharmacology; D010507:Periodicity; D010775:Photic Stimulation; D017729:Presynaptic Terminals / Q000378:metabolism*; D012160:Retina / Q000737:chemistry / Q000166:cytology* / Q000378:metabolism*; D014785:Vision, Ocular / Q000187:drug effects / Q000502:physiology*
D000613:Aminobutyrates; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D018690:Excitatory Amino Acid Agonists; C012729:2-amino-4-phosphonobutyric acid; D009543:Nifedipine; D002118:Calcium