title: Voltage-dependent K+channels improve the energy efficiency of signalling in blowfly photoreceptors.
abstract: Voltage-dependent conductances in many spiking neurons are tuned to reduce action potential energy consumption, so improving the energy efficiency of spike coding. However, the contribution of voltage-dependent conductances to the energy efficiency of analogue coding, by graded potentials in dendrites and non-spiking neurons, remains unclear. We investigate the contribution of voltage-dependent conductances to the energy efficiency of analogue coding by modelling blowfly R1-6 photoreceptor membrane. Two voltage-dependent delayed rectifier K+conductances (DRs) shape the membrane's voltage response and contribute to light adaptation. They make two types of energy saving. By reducing membrane resistance upon depolarization they convert the cheap, low bandwidth membrane needed in dim light to the expensive high bandwidth membrane needed in bright light. This investment of energy in bandwidth according to functional requirements can halve daily energy consumption. Second, DRs produce negative feedback that reduces membrane impedance and increases bandwidth. This negative feedback allows an active membrane with DRs to consume at least 30% less energy than a passive membrane with the same capacitance and bandwidth. Voltage-dependent conductances in other non-spiking neurons, and in dendrites, might be organized to make similar savings.
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK fjhheras@gmail.com.
authors.forename: Francisco J H
authors.identifier: 0000-0001-8124-2359
authors.initials: FJ
authors.lastname: Heras
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK.
authors.forename: John
authors.identifier: 0000-0001-5946-6313
authors.initials: J
authors.lastname: Anderson
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK.
authors.forename: Simon B
authors.identifier: 0000-0003-4659-6543
authors.initials: SB
authors.lastname: Laughlin
authors.affiliation: School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, UK.
authors.forename: Jeremy E
authors.identifier: 0000-0001-7786-5254
authors.initials: JE
authors.lastname: Niven
mesh_terms: D000200:Action Potentials; D000818:Animals; D004175:Diptera / Q000502:physiology*; D004553:Electric Conductivity; D004734:Energy Metabolism; D019476:Insect Proteins / Q000502:physiology*; D015640:Ion Channel Gating; D008564:Membrane Potentials; D008954:Models, Biological; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated / Q000502:physiology*
chemical_list: D019476:Insect Proteins; D024642:Potassium Channels, Voltage-Gated
keywords: analogue coding; energy-aware bandwidth and gain control; insect graded-potential neuron; membrane impedance; negative feedback; voltage-sensitive potassium conductance