Mitochondrial lenses found in retinal cells

(ORDO NEWS) — Mitochondria are organelles that produce ATP to provide energy to cells. Their role is so important that mitochondria are present in every cell in abundance.

They are found even in the inner part of the cones – the sensitive cells of the retina. And there they have another useful function, refracting and focusing light on protein receptors that perceive light.

In fact, light passing through the lens enters the retina, where sensitive cells are located – cones and rods. Each cone resembles a spindle on a long stalk, and photons need to travel its entire length before reaching the top of the “spindle”, in its outer segment, where the proteins that perceive them are located.

Therefore, the structures of the cones are as transparent as possible. However, in the path of the light there is a dense accumulation of mitochondria located in the outer segment. Scientists have long wondered what role they play there? After all, theoretically, these mitochondria should prevent the passage of photons.

Mitochondrial lenses found in retinal cells 2

To unravel this mystery, Wei Li and colleagues at the National Eye Institute (NEI) experimented with retinal samples from 13-striped ground squirrels ( Ictidomys tridecemlineatus ): these animals have poor vision in the dark, and their retinas contains few rods, but is very rich in cones.

Animals were euthanized, their retina was taken, after which only a layer of sensitive cells was isolated, which were studied under a confocal microscope. This made it possible to see how light changes as it passes through the cones and their dense clusters of mitochondria.

It was found that instead of scattering light, the mitochondria concentrated it, sending it further to the outer segment receptors. This was also confirmed by computer simulations: the accumulation of mitochondria in the cone acts as an additional lens, focusing the radiation passing through it even more.

According to the authors, this function of mitochondria can also explain the phenomenon known as the Stiles-Crawford effect . It consists in the fact that light entering the retina at more direct angles is perceived as brighter than coming from the periphery.

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