Can retinal emit as well as absorb photons?

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In summary, based on your anecdote and speculation, it seems that retinal molecules can emit photons of light, though this may be rare due to the complex process of rhodopsin regeneration.
  • #1
Yamayama
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Retinal: the molecules which absorb photons of light in the photoreceptors at the back of our eyes; they combine with an opsin molecule to form photopigments.

It seems to me that: just as isomerization of retinal from 11-cis-retinal to all-trans-retinal corresponds to the absorption of a photon, changing back from all-trans-retinol to 11-cis-retinol - which is a necessary step for rhodopsin regeneration - surely corresponds to the emission of a photon.

If my suspicion is correct, I guess the reason this isn't observed is because rhodopsin regeneration occurs in the RPE (retinal pigmented epithelium, which is high in melanin - fantastic for absorbing light).

Can anyone affirm/disaffirm my suspicions?
 
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  • #2
Subjectively speaking, yes. Looking closely into one woman's eyes I once felt that way. It was the most intimate communication I had ever experienced in public. Her eyes were dilated, and I could see the heartbeat in her irises. But photons? More like epiphany.
 
  • #3
While there are generally 2 ways any reaction can go, implying that anything that absorbs light can emit it, I bet the non-emitting relaxation processes are dominant.

Also, everything emits blackbody radiation, but that is trivial.

Njorl
 
  • #4
Subjectively speaking, yes. Looking closely into one woman's eyes I once felt that way. It was the most intimate communication I had ever experienced in public. Her eyes were dilated, and I could see the heartbeat in her irises. But photons? More like epiphany.

hmmmm...nice anecdote...well, I was hoping more for an objective response, but hey...lucky you!

Njorl:
You're quite possibly right.

The events involved in rhodopsin regeneration are quite complex I expect, and I'm not sure they're even fully understood yet.

Also, it's just been pointed out to me that if a photon is emitted, its energy is not necessarily in the visible range, i.e. it could be infrared.
 
  • #5
You might be interested in the following papers :approve:

Nature. 1976 Apr 22;260(5553):675-8.
Observation of light emission from a rhodopsin.
Lewis A, Spoonhower JP, Perreault GJ.
PMID: 1264238 [PubMed]

Photochem Photobiol. 1982 Mar;35(3):385-90.
Light-induced change in rhodopsin emission: phosphorescence and fluorescence.
Andley UP, Chakrabarti B.
PMID: 7063554 [PubMed]

I'm not sure how common light emission from rhodopsin is, since the conformational change from cis to trans is biochemically coupled to downstream signalling cascades. It would depend how soon the energy transfer to an electrical signal can happen when it it goes into trans, and how readily it is able to go back into cis with the emission of a photon.

You are right, the color absorped most by rhodopsin is purple, so it is to be expected that the emitted photon would be in the infrared (longer wavelength).
 
  • #6
Thanks very much Monique,

I should have thought of searching PubMed myself of course. Anyway, unfortunately I can't seem to get those articles online, as issues that old aren't available in their online catalogs, but maybe I can figure out another way to get them.
Appreciate the help
 
  • #7
Ask a librarian to fetch a copy for you, those issues are probably still standing in some library and they'll know where :)
 

1. How does the retina emit photons?

The retina does not emit photons on its own. It is not a light source like the sun or a light bulb. Instead, the retina is responsible for absorbing photons that enter the eye from external light sources.

2. Can the retina emit photons in the absence of external light?

No, the retina cannot emit photons in the absence of external light. The retina requires external light sources to function and cannot produce its own light.

3. How does the retina absorb photons?

The retina contains specialized cells called photoreceptors, which are responsible for absorbing photons. These photoreceptors contain pigments that are sensitive to different wavelengths of light. When light enters the eye, it stimulates these pigments and triggers a cascade of biochemical reactions that ultimately send signals to the brain, allowing us to see.

4. Can the retina emit and absorb photons at the same time?

No, the retina cannot emit and absorb photons at the same time. When light enters the eye, the retina's photoreceptors are either absorbing photons or in a resting state, but they cannot do both simultaneously.

5. Can the retina emit photons in response to certain stimuli?

No, the retina does not emit photons in response to stimuli. Its main function is to absorb photons and convert them into electrical signals that are sent to the brain. However, some studies have shown that certain chemicals or drugs can stimulate the retina to emit light, but this is not a natural or common occurrence.

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