Some very transparent cells in the optical tract of vertebrates, such as the lens fiber cells, possess certain types of specialized intermediate filaments (IFs) that have essential significance for their transparency. The exact mechanism describing why the IFs are so important for transparency is unknown. Recently, transparency was described also in the retinal Müller cells (MCs). We report that the main processes of the MCs contain bundles of long specialized IFs, each about 10 nm in diameter; most likely, these filaments are the channels providing light transmission to the photoreceptor cells in mammalian and avian retinas. We interpret the transmission of light in such channels using the notions of quantum confinement, describing energy transport in structures with electroconductive walls and diameter much smaller than the wavelength of the respective photons. Model calculations produce photon transmission efficiency in such channels exceeding 0.8, in optimized geometry. We infer that protein molecules make up the channels, proposing a qualitative mechanism of light transmission by such structures. The developed model may be used to describe light transmission by the IFs in any transparent cells.

The specialized intermediate filaments (IFs) have critical importance for the clearness and uncommon transparency of the vertebrates' lens fiber cells, although the physical mechanisms involved are poorly understood. Recently, an unusual low-scattering light transport was also described in the retinal Müller cells. Exploring the function of the IFs in the Müller cells, we have studied the morphology and distribution pattern of the IFs and other cytoskeletal filaments inside the Müller cell main processes in the foveolar part of the avian (Pied Flycatcher) retina. We found that some IFs surrounded by globular nanoparticles (that we suggest are crystallines) are present in almost every part of the Müller cells that span the retina, including the microvilli. Unlike the IFs implicated in the mechanical architecture of the cell, these IFs are not connected to any specific cellular membranes. Instead, they are organized into bundles, passing inside the cell from the endfeet to the photoreceptor, following the geometry of the processes and repeatedly circumventing numerous obstacles. We believe that all of the presently reported data effectively confirms that the model of nanooptical channels built of the intermediate filaments [Makarov et al., 2015, Khmelinskii et al., 2015] may provide a viable explanation of the Müller cell transparency.

Presently we continue our studies of the quantum mechanism of light energy transmission in the form of excitons by axisymmetric nanostructures with electrically conductive walls. Using our theoretical model, we analyzed the light energy transmission by biopolymers forming optical channels within retinal Müller cells. There are specialized intermediate filaments (IF) 10 – 18 nm in diameter, built of electrically conductive polypeptides. Presently, we analyzed the spectral selectivity of these nanostructures. We found that their transmission spectrum depends on their diameter and wall thickness. We also considered the classical approach, comparing the results with those predicted by the quantum mechanism. We performed experimental measurements on model quantum waveguides, made of rectangular nanometer-thick chromium (Cr) tracks. The optical spectrum of such waveguides varied with their thickness. We compared the experimental absorption/transmission spectra with those predicted by our model, with good agreement between the two. We report that the observed spectra may be explained by the same mechanisms as operating in metal nanolayers. Both the models and the experiment show that Cr nanotracks have high light transmission efficiency in a narrow spectral range, with the spectral maximum dependent on the layer thickness. Therefore, a set of intermediate filaments with different geometries may provide light transmission over the entire visible spectrum with a very high (∼90%) efficiency. Thus, we believe that high contrast and visual resolution in daylight are provided by the quantum mechanism of energy transfer in the form of excitons, whereas the ultimate retinal sensitivity of the night vision is provided by the classical mechanism of photons transmitted by the Müller cell light-guides.

The metabolic scaling in the animal has been discussed for over 90 years, but no consensus has been reached. Our analysis of 2126 species of vertebrates reveals a significant allometric exponent heterogeneity. We show that classes of terrestrial vertebrates exhibit the evolution of metabolic scaling. Both the allometric coefficient “a” and the allometric exponent “b” change naturally, but differently depending on the geological time of group formation. The allometric coefficient “a” shows the measure of the evolutionary development of systems that forms resting metabolism in animals. Endothermic classes, such as birds and mammals, have a metabolic rate that is in an order of magnitude higher than that in ectothermic classes, including amphibians and reptiles. In the terrestrial vertebrate phylogeny, we find that the metabolic scaling is characterized by 3 main allometric exponent values: b = 3/4 (mammals), b > 3/4 (ectotherms, such as amphibians and reptiles), and b < 3/4 (birds). The heterogeneity of the allometric exponent is a natural phenomenon associated with the general evolution of vertebrates. The scaling factor decreases depending on both the external design and the size (birds vs mammals) of the animal. The metabolic rate and uniformity of species within a class increase as the geological start date of formation of the class approaches the present time. The higher the mass‐specific standard metabolic rate in the class, the slower metabolic rate grows with increasing body size in this class. Our results lay the groundwork for further exploration of the evolutionary and ecological aspects of the development of metabolic scaling in animals.

Birds which possess high visual acuity, such as eagles and falcons, are known to have retinas with a deep conically curved central foveal pit. There have been different attempts to explain the importance of this particular shape of the fovea in visual resolution. Recently, the function of Müller cells as “light fibers” was discovered, showing how the endfeet of Müller cells trap the light and then transfer it to a single cone photoreceptor. Here we describe how the endfeet of Müller cells line the walls of the foveal pit in the Pied Flycatcher, and how the Müller cell body extends its processes towards individual cones, forming machinery that could allow for light transfer from the pit wall to the photoreceptor layer alongside the pit. We describe how this construction may send an image from the fovea to the cones, and also, how the angular positioning of Müller cells, being optical extensions of the cones, has the advantage of being much denser than on a flat or slightly curved fovea. We, therefore, suggest that this type of optic fiber alignment can be used as a novel type of “amplifying array” that simply increases the amount of megapixels at the photoreceptor cell layer.

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Analysis of metabolic scaling in currently living endothermic animal species allowed us to show how the relationship between body mass and the basal metabolic rate (BMR) has evolved in the history of endothermic vertebrates. We compared six taxonomic groups according to their energetic characteristics and the time of evolutionary divergence. We transformed the slope of the regression lines to the common value and analyzed three criteria for comparing BMR of different taxa regardless of body size. Correlation between average field metabolic rate (FMR) of the group and its average BMR was shown. We evaluated the efficiency of self-maintenance in ordinary life (defined BMR/FMR) in six main groups of endotherms. Our study has shown that metabolic scaling in the main groups of endothermic animals correlates with their evolutionary age: the younger the group, the higher the metabolic rate, but the rate increases more slowly with increasing body weight. We found negative linear relationship for scaling exponents and the allometric coefficient in five groups of endotherms: in units of mL O2/h per g, in relative units of allometric coefficients, and also in level or scaling elevation. Mammals that diverged from the main vertebrate stem earlier have a higher “b” exponent than later divergent birds. A new approach using three criteria for comparing BMR of different taxa regardless of body mass will be useful for many biological size-scaling relationships that follow the power function.

Endothelial microvilli that protrude into the capillary lumen, although invisible in the optical microscopy, may play an important role in the blood flow control in the capillaries. Because of the plug effects, the width of the gap between the capillary wall and the blood cell is especially critical for the blood flow dynamics in capillaries, while microvilli located on the capillary wall can easily control the velocity of the blood flow. We report that microvilli in the capillaries of different vertebrate species have similar characteristics and density, suggesting similarities between the respective regulation mechanisms. A simplified physical model of the capillary effective diameter control by the microvilli is presented.