title: Cellular elements for seeing in the dark: voltage-dependent conductances in cockroach photoreceptors.
abstract: BACKGROUND
  The importance of voltage-dependent conductances in sensory information processing is well-established in insect photoreceptors. Here we present the characterization of electrical properties in photoreceptors of the cockroach (Periplaneta americana), a nocturnal insect with a visual system adapted for dim light.
  
  
  RESULTS
  Whole-cell patch-clamped photoreceptors had high capacitances and input resistances, indicating large photosensitive rhabdomeres suitable for efficient photon capture and amplification of small photocurrents at low light levels. Two voltage-dependent potassium conductances were found in the photoreceptors: a delayed rectifier type (KDR) and a fast transient inactivating type (KA). Activation of KDR occurred during physiological voltage responses induced by light stimulation, whereas KA was nearly fully inactivated already at the dark resting potential. In addition, hyperpolarization of photoreceptors activated a small-amplitude inward-rectifying (IR) current mediated at least partially by chloride. Computer simulations showed that KDR shapes light responses by opposing the light-induced depolarization and speeding up the membrane time constant, whereas KA and IR have a negligible role in the majority of cells. However, larger KA conductances were found in smaller and rapidly adapting photoreceptors, where KA could have a functional role.
  
  
  CONCLUSIONS
  The relative expression of KA and KDR in cockroach photoreceptors was opposite to the previously hypothesized framework for dark-active insects, necessitating further comparative work on the conductances. In general, the varying deployment of stereotypical K+ conductances in insect photoreceptors highlights their functional flexibility in neural coding.
authors.affiliation: Department of Physics, University of Oulu, Oulu, Finland.
authors.forename: Iikka
authors.initials: I
authors.lastname: Salmela
authors.forename: Esa-Ville
authors.initials: EV
authors.lastname: Immonen
authors.forename: Roman
authors.initials: R
authors.lastname: Frolov
authors.forename: Stephan
authors.initials: S
authors.lastname: Krause
authors.forename: Yani
authors.initials: Y
authors.lastname: Krause
authors.forename: Mikko
authors.initials: M
authors.lastname: Vähäsöyrinki
authors.forename: Matti
authors.initials: M
authors.lastname: Weckström
mesh_terms: D000818:Animals; D055592:Biophysical Phenomena / Q000187:drug effects / Q000502:physiology*; D003058:Cockroaches; D003198:Computer Simulation; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008027:Light; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D008954:Models, Biological; D018408:Patch-Clamp Techniques; D010775:Photic Stimulation; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D019789:Tetraethylammonium / Q000494:pharmacology
chemical_list: D026902:Potassium Channel Blockers; D015221:Potassium Channels; D019789:Tetraethylammonium; D011188:Potassium