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Retinal phosphenes and discrete dark noises in rods: a new biophysical framework
István Bókkon1, Ram Lakhan Pandey Vimal
1Doctoral School of Pharmaceutical and Pharmacological Sciences, Semmelweis University, H-1085 Ulloi út 26, Budapest, Hungary. bokkoni@yahoo.com
Journal of Photochemistry and Photobiology. B, Biology
|August 1, 2009
Summary
Discrete dark noise in rod cells may originate from natural bioluminescent photons produced by lipid peroxidation in the retina, reconciling energy discrepancies in rhodopsin activation. This suggests a novel source for visual noise.
Area of Science:
- Biophysics
- Photochemistry
- Neuroscience
Background:
- Spontaneous rhodopsin activation generates discrete noises similar to single-photon responses, but with a significant discrepancy in activation energy compared to photon-driven processes.
- Existing hypotheses suggest different molecular mechanisms for thermal versus photon activation of rhodopsin, with a low-energy thermal pathway linked to Schiff base deprotonation in a rhodopsin subpopulation.
- Ionizing radiation can induce free radicals, leading to lipid peroxidation and chemiluminescent photons that trigger phosphene perception by activating photoreceptors.
Purpose of the Study:
- To propose a novel hypothesis for the origin of discrete dark noise in rod photoreceptors.
- To reconcile the observed discrepancy in activation energies between thermal and photon-driven rhodopsin activation.
- To explore the role of endogenous bioluminescent photons in visual perception and noise generation.
Main Methods:
- Theoretical analysis and synthesis of existing experimental data on rhodopsin activation energies and lipid peroxidation.
- Comparison of energy barriers for photon activation versus thermal activation of rhodopsin.
- Evaluation of the potential contribution of naturally occurring bioluminescent photons to dark noise in rod cells.
Main Results:
- The study highlights a significant difference in activation energies: ~40-50 cal/mol for photon activation versus ~20-25 kcal/mol for thermal activation of rhodopsin.
- It is proposed that natural, low-level bioluminescent photons, generated by ongoing lipid peroxidation in the retina, can activate rhodopsin.
- This endogenous photon emission is suggested to be non-negligible in dark-adapted retinal cells, particularly given the high oxygen demand and polyunsaturated fatty acid content of photoreceptors.
Conclusions:
- Discrete dark noise in rod photoreceptors may be caused by endogenous bioluminescent photons arising from retinal lipid peroxidation.
- This hypothesis offers a potential explanation for the energy discrepancy observed in spontaneous rhodopsin activation.
- The findings suggest that natural bioluminescence plays a role in visual noise, distinct from external light stimulation.
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