title: Distinct roles of light-activated channels TRP and TRPL in photoreceptors ofPeriplaneta americana.
abstract: Electrophysiological studies inDrosophila melanogasterandPeriplaneta americanahave found that the receptor current in their microvillar photoreceptors is generated by two light-activated cationic channels, TRP (transient receptor potential) and TRPL (TRP-like), each having distinct properties. However, the relative contribution of the two channel types to sensory information coding by photoreceptors remains unclear. We recently showed that, in contrast to the diurnalDrosophilain which TRP is the principal phototransduction channel, photoreceptors of the nocturnalP. americanastrongly depend on TRPL. Here, we perform a functional analysis, using patch-clamp and intracellular recordings, ofP. americanaphotoreceptors after RNA interference to knock down TRP (TRPkd) and TRPL (TRPLkd). Several functional properties were changed in both knockdown phenotypes: cell membrane capacitance was reduced 1.7-fold, light sensitivity was greatly reduced, and amplitudes of sustained light-induced currents and voltage responses decreased more than twofold over the entire range of light intensities. The information rate (IR) was tested using a Gaussian white-noise modulated light stimulus and was lower in TRPkd photoreceptors (28 ± 21 bits/s) than in controls (52 ± 13 bits/s) because of high levels of bump noise. In contrast, although signal amplitudes were smaller than in controls, the mean IR of TRPLkd photoreceptors was unchanged at 54 ± 29 bits/s1because of proportionally lower noise. We conclude that TRPL channels provide high-gain/high-noise transduction, suitable for vision in dim light, whereas transduction by TRP channels is relatively low-gain/low-noise and allows better information transfer in bright light.
authors.affiliation: Biophysics Group, Nano and Molecular Systems Research Unit, University of Oulu, Oulu FI-90014, Finland.
authors.forename: Paulus
authors.identifier: http://orcid.org/0000-0003-1858-8474
authors.initials: P
authors.lastname: Saari
authors.affiliation: Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada.
authors.forename: Andrew S
authors.initials: AS
authors.lastname: French
authors.affiliation: Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada.
authors.forename: Päivi H
authors.identifier: http://orcid.org/0000-0002-8205-7339
authors.initials: PH
authors.lastname: Torkkeli
authors.affiliation: Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada.
authors.forename: Hongxia
authors.identifier: http://orcid.org/0000-0002-9232-5122
authors.initials: H
authors.lastname: Liu
authors.affiliation: Biophysics Group, Nano and Molecular Systems Research Unit, University of Oulu, Oulu FI-90014, Finland.|Lund Vision Group, Department of Biology, Lund University, 223 62 Lund, Sweden.
authors.forename: Esa-Ville
authors.identifier: http://orcid.org/0000-0002-5576-0627
authors.initials: EV
authors.lastname: Immonen
authors.affiliation: Biophysics Group, Nano and Molecular Systems Research Unit, University of Oulu, Oulu FI-90014, Finland roman.frolov@oulu.fi.
authors.forename: Roman V
authors.identifier: http://orcid.org/0000-0002-7431-5297
authors.initials: RV
authors.lastname: Frolov
mesh_terms: D000200:Action Potentials; D000818:Animals; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism*; D055537:Light Signal Transduction; D010526:Periplaneta / Q000378:metabolism / Q000502:physiology; D017956:Photoreceptor Cells, Invertebrate / Q000378:metabolism* / Q000502:physiology; D050051:Transient Receptor Potential Channels / Q000235:genetics / Q000378:metabolism*
chemical_list: D019476:Insect Proteins; D050051:Transient Receptor Potential Channels