Calcium and calcium-dependent chloride currents generate action potentials in solitary cone photoreceptors.
Vertebrate rod and cone photoreceptors hyperpolarize when illuminated. However, synaptic input from horizontal cells can depolarize cones and even elicit action potentials. Using the whole-cell tight-seal recording technique, we determined that, in solitary cones isolated from a lizard retina, action potentials can be generated by depolarizing current steps under conditions where only two ionic currents are activated. A dihydropyridine-sensitive, inward Ca2+ current that activates at potentials positive to -40 mV can regeneratively depolarize the cell. Subsequently, a SITS-sensitive, Ca2(+)-dependent outward Cl- current repolarizes the cell. We suggest that these ionic currents may help explain lateral inhibition in the retina.
Maricq
A V
AV
Department of Physiology School of Medicine, University of California, San Francisco 94143.
Korenbrot
J I
JI
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D018118:Chloride Channels; D002712:Chlorides / Q000502:physiology*; D004553:Electric Conductivity; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008116:Lizards; D008565:Membrane Proteins / Q000502:physiology*; D010786:Photoreceptor Cells / Q000502:physiology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D018118:Chloride Channels; D002712:Chlorides; D007473:Ion Channels; D008565:Membrane Proteins; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D002118:Calcium