The role of diffusion in the photoresponse of an extraretinal photoreceptor of Aplysia.
- 1 February 1979
- journal article
- research article
- Published by Wiley in The Journal of Physiology
- Vol. 287 (1), 283-301
- https://doi.org/10.1113/jphysiol.1979.sp012659
Abstract
Membrane currents produced by flashes and steps of light (photo-current) were recorded from the ventral photoresponsive neuron of Aplysia californica. The effects of background illumination and changes in temperature were also examined. The falling phase of the response wave form may be separated into 2 components with time constants of 10-12 s and 50 s. Background illumination reduced the response amplitude to light impulses without appreciably altering the response wave form. Lowering the temperature greatly reduced the amplitude of the photo-current with a Q10 of 2.91 (25-15.degree. C) and greatly prolonged the duration of the response. Because of the relatively large distance between the plasma membrane and the pigmented cytoplasmic lipochondria where light is absorbed, a diffusion-based model with Ca as the internal-transmitter was developed. In this model diffusion of Ca2+ released from the lipochondria upon photon absorption is slowed by the reversible uptake of Ca2+ at cytoplasmic binding sites. Ca2+ interacts with sites at the plasma membrane to increase GK [membrane K conductance] and Ca2+ levels are subsequently restored by irreversible uptake processes. Ca2+ release and its adsorption and desorption from the more numerous plasma membrane binding sites were assumed to be instantaneous with respect to the duration of the light-evoked response. The linearized model equations adequately predict the experimental response wave forms, the effects of temperature, and saturation of the steady-state amplitude-stimulus relationship. Aside from amplitude scaling, no curve-fitting was used. The model also gives realistic values for the cytoplasmic diffusion coefficient of Ca and the net rate of Ca efflux required to restore dark Ca activity.This publication has 20 references indexed in Scilit:
- Isolation of pigmented granules involved in extra-retinal photoreception in Aplysia californica neuronsBiochimica et Biophysica Acta (BBA) - Biomembranes, 1977
- Lipochondria and the light response of Aplysia giant neuronsJournal of Neurobiology, 1977
- Intracellular calcium and extra-retinal photoreception inAplysia giant neuronsJournal of Neurobiology, 1977
- Sodium-calcium exchange and calcium-calcium exchange in internally dialyzed squid giant axonsThe Journal of Membrane Biology, 1975
- Light-Induced Changes in the Structure of Pigmented Granules in Aplysia NeuronsScience, 1975
- Light Response of a Giant Aplysia NeuronThe Journal of general physiology, 1973
- The Visual Process: Excitatory Mechanisms in the Primary Receptor CellsAnnual Review of Biophysics and Bioengineering, 1972
- The Ferrier Lecture, 1962 Visual adaptationProceedings of the Royal Society of London. B. Biological Sciences, 1965
- The Rat ElectroretinogramThe Journal of general physiology, 1964
- A study of the nucleus and cell membranes of oocytes with an intra-cellular electrodeExperimental Cell Research, 1963