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Mechanical and Optical Properties of Müller Cells
Müller cells, the principal glial cells of the vertebrate retina, are the only cells spanning its entire
thickness, suggesting an important contribution to the stability of the tissue.
They are thought to be involved in the genesis of different retinal diseases, e.g. retinal
detachment or retinoschisis, in which mechanical stress plays an important role. Thus, we
investigated the mechanical properties of Müller cells and of retinal neurons.
The mechanical properties of living cells depend mainly on the cytoskeleton. Along a single
Müller cell, the composition of the cytoskeleton changes within the different retinal layers,
suggesting different mechanical properties in different segments.
We analyzed the viscoelastic properties at different locations along Müller cells (endfoot, inner
process, soma) and of Bipolar cell somata by using atomic force microscopy (AFM), singleparticle-tracking and optical stretching. Moreover, we started to compare healthy cells with cells
taken from transgenic mice in order to explore the possible underlying concepts of Müller cell
involvement in different diseases.
In conclusion, we can state that Müller cell processes and endfeet showed higher elasticity (i.e.
they are stiffer) than their somata. Compared to bipolar cell somata, Müller cell somata were
shown to be less elastic (i.e. softer). The viscoelastic behavior of healthy and transgenic cells
seems to differ.
Since the retina of vertebrates is a so-called inverted retina, the light has to pass several cell
layers, meaning several refractive elements, before it reaches the photoreceptor cells. Here it is
being converted to electrical impulses which are then sent to the brain.
Laser Scanning Microscope images of retinal wholemounts taken in reflection mode reveal
structures which seem to guide the light through the retina to the photoreceptors. The dimension
and distribution of these structures resembles that of Müller cells. Thus, we investigated the
optical properties of individual Müller cells with a modified two-beam laser trap and showed
directly that they are in fact light guides that even display saturable transmission.
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