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Spread of activation and desensitisation in rod outer segments
Nature
|January 3, 1980
Summary
Visual transduction involves a diffusible transmitter linking light absorption to cell response. Both activation and desensitization spread locally, with effects diminishing within 8 micrometers of light absorption in photoreceptors.
Area of Science:
- Neuroscience
- Cell Biology
- Photoreceptor Physiology
Background:
- Vertebrate photoreceptors utilize a diffusible internal transmitter for visual transduction.
- Photon absorption in disk membranes triggers a conductance decrease in the outer segment plasma membrane.
- Desensitization of the photoresponse suggests involvement of a diffusible substance, as one photon can desensitize responses to subsequent photons.
Purpose of the Study:
- To investigate the spatial spread of activation and desensitization in photoreceptors.
- To determine the effective range of the diffusible transmitter and desensitizing substance.
Main Methods:
- Experiments involving dim illumination of photoreceptors.
- Measurement of the spatial extent of photoresponse activation and desensitization.
Main Results:
- Both photoresponse activation and desensitization spread longitudinally from the site of photon absorption.
- These effects decline to be half-maximal within 8 micrometers of the light absorption site under dim illumination.
Conclusions:
- The internal transmitter and desensitizing substance in photoreceptors have a limited diffusion range.
- Activation and desensitization processes are localized, not spreading throughout the entire outer segment.