How many mitochondria in a muscle cell

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Building with DNA June 10, Subcellular chatter regulates longevity May 18, In apoptosis the mitochondrion releases a chemical, cytochrome c, and this can trigger programmed cell death apoptosis. Mitochondria are also thought to influence, by exercising a veto, which eggs in a woman should be released during ovulation and which should be destroyed by programmed cell death apoptosis.

This is part of a process called atresia. It appears that in this process mitochondria and the nucleus of the cell in which the mitochondria reside, are screened for biochemical compatibility.

The pairs that are incompatible are shut down by programmed cell death. Mitochondria: generators of disorders and disease Mitochondria are very important energy converters. In this process they produce waste products. In mitochondria these are called reactive oxygen species ROSs. These mutations are the source of mitochondrial disease that can affect areas of high energy demand such as brain, muscles, central nervous system and the eye.

Mutations caused by ROSs have been suggested as contributing to the ageing process. Many more mutations in mitochondrial DNA take place in people over 65 than in younger people, but many more factors are involved in this inevitable at present but variable process. The working of mitochondria at a molecular level is also involved in the good or otherwise progress of people in the very early stages of recovery following open heart and transplant surgery. It appears that the drugs damage mitochondria and block the production of mitochondrial DNA.

French and Japanese centenarians appear to have advantageous mutations in their mitochondrial DNA. This is interesting but since we do not know about cause and effect, care needs to be exercised when considering these figures. In the field of sport it is not difficult to reason that athletes with high counts of mitochondria in their heart and other appropriate muscle cells are able to do just that little bit better than others less well endowed. Mitochondria: providers of genetic history Mitochondria are virtually cells within a cell and each one has its own DNA.

Mitochondrial DNA is only inherited through the maternal line. Any mitochondrial DNA contributed by the father is actively destroyed by programmed cell death after a sperm fuses with an egg. This interesting situation has provided geneticists and anthropologists with a very useful analytical and measuring tool.

Over the years maternal mitochondrial DNA has been inherited in a direct line never having been combined or shuffled with DNA from mitochondria of the male line. Some people are sceptical about this idea but strong evidence in support of it is accumulating. Mitochondria: an organelle probably used to boost the success rate of infertility treatment. The sectional area of each muscle cell profile minus the nucleus and of each mitochondrion was measured, in order to obtain the mitochondrial spatial density.

The same image as in C. Each muscle cell profiles bears a double set of digits, the first indicating the assigned number to that cell and the second indicating the number of the section in the series. For example the nucleated cell profile at the top of A. From the same preparation illustrated in Fig. Their mitochondria are filled-in in black.

Over the sequence there is a remarkable change in shape of the profiles of the two cells, whose space relationship also varies rapidly; it should also be noted how un-smooth these cell profiles are. The number of mitochondria varies considerable between the individual profiles; however, their average spatial density over the series is close to the one calculated for the whole bundle.

Data on other animal species were collected but were not sufficiently extensive for proper quantitation. In a large preparation of the ileum, muscle cell profiles of the circular layer contained 1, mitochondria, which occupied 4. In the shrew a small mammal with a body weight below 10 g , in a large preparation of the ileum muscle cell profiles of the circular layer contained 1, mitochondria, which occupied 5. Mitochondrial density in smooth muscles of amphibian was assessed in margin of the present study.

Typically, in the small intestine of the Axolotl the mitochondrial density in muscle cells was 1. Similar values were obtained from intestinal muscles of fish ray fish and angler fish.

In a few hundred muscle cells of the small intestine of turtles and chickens the mitochondrial density was consistently within the 2. The first concern to discuss is about the reliability of the procedures used, and their limitations. Many methods have been used for quantitative studies of mitochondria, the majority based on biochemical assays 13 , 14 , Some of them have great attraction, but all have considerable and well-acknowledged limitations; in addition, the very question of what is meant with quantitative evaluation of the chondrioma has complex theoretical aspects.

On the one hand, the morphometric method used in this study, based on electron micrographs and a graphics software, can be very accurate in outlining the objects to be measured, in obtaining their dimensions and in producing a permanent and accessible digital record of the entire procedure — images, measurements, calculations.

All the materials can be revisited for checks and further analysis. The mitochondria all of them and only them can be readily identified microscopically, and there is no risk of contamination from other cellular elements or from mitochondria of other cell types within the tissue.

A further attraction of the method is that the data are partly figurative, rather than entirely numerical, a possible advantage in the eye of morphologists. On the other hand, a difficulty of the method is its reliance on adequate preservation of the tissues for microscopy. Preparation artifacts affecting the mitochondria such a shrinkage, swelling, cutting compression are hard to avoid entirely, and more difficult still it is to recognize whether an artifact is present or not.

A further important weakness of this work is that all mitochondria were regarded as equal, varying only in size and number, which is surely an oversimplification, even if it is currently the basic assumption in the literature on smooth muscle. In other fields, chemical and structural differences among mitochondria have been observed, as was mentioned in the Introduction.

The first conclusion to draw from the data is that the mitochondrial density, that is, the percentage of the cytoplasm volume or of the cell volume minus the nucleus that is occupied by mitochondria, varies markedly in different smooth muscles, roughly from less than 2 to almost 10 percent.

Even the highest values observed are small by comparison with those of skeletal muscles and very small by comparison with those of cardiac muscle. For example, Park, et al. Looking at other Vertebrates, including fishes, reptiles and amphibians preliminary observations not illustrated here the mitochondrial density was lower than in mammals but it never fell below about 1.

Looking at other Vertebrates, including cold-blooded species of fishes, reptiles and amphibians preliminary observations, not illustrated here the mitochondrial density was lower than in mammals but it never fell below about 1.

The large differences in mitochondrial spatial density in different muscles that are observed by microscopy are regarded as genuine differences between the tissues and not as artifacts , and variations of this magnitude raise many questions. The variation may have biological significance in two respects. First, the variation in the spatial density of mitochondria may impart but not necessarily some different functional property to each muscle. The second conclusion is that the ample variation of mitochondrial density is in contrast with its relative uniformity within a given muscle in a given animal species.

It is true that different experiments on the same material show some variability, and, even if some variability is introduced and is accounted for by the method used, some of it is surely a property of the tissue itself. So, for example, in the case of the tenia coli variability between preparations is quite evident.

Nevertheless, there is no overlap in the range of the values for the tenia with those for the ileum of the same species, allowing the conclusion to be made that there is a range of spatial density values that is characteristic of each muscle type or animal species.

Similarly, while the results from the guinea-pig ileum are not identical in different experiments, nevertheless there is no overlap in the data from the experiments on the ileum of mice, rats, guinea-pigs and sheep; each one of the four species seems to have a characteristic non-overlapping range of values for their chondrioma.

A third point concerns the variability of mitochondrial density among the cells of a given muscle, suggesting the presence of some species-specific mechanisms. In an individual muscle cell profile the value of mitochondrial spatial density has no interest: it amounts to a measurement on a small fraction of a one hundredth of the volume of that cell a section of 0. Serial sections, in contrast, are interesting because they allow measurements to be made on several profiles from the same muscle cell.

In the work with serial sections the larger the number of sections of a single cell that are examined, the closer the value of mitochondrial density for that cell gets to the average value for the whole muscle. How much variation would remain if one had access to all the sections of a single cell through its entire length, cannot be established. This is the conclusion offered by the rat detrusor muscle; its validity also for other smooth muscles seems probable, but remains to be proved.

The mitochondrial density, therefore, appears to be somehow regulated, around small oscillations and with small differences between the cells of the same muscle.

What are the possible regulation mechanisms, and how they work, is unknown. It should also be noted that a given percentage value of spatial density depends on at least two factors, the mitochondria themselves on the one hand, and the rest of the cell on the other: for example, mitochondria might be entirely static but their density could fall because of an increase in the volume of the contractile material in the cell. Processes bringing in new mitochondria or eliminating old ones are known in many cell types 27 , 28 , 29 , including bladder smooth muscle 30 ; however, nothing can be said yet as to the role of mitogenesis and mitophagy in the comparative difference described here.

As a fourth conclusion, in the circular musculature of the ileum there is intra-species consistence in mitochondrial density, as discussed, but also a characteristic variation between the four species studied. There is some correlation between mitochondrial density of visceral muscle cells and the body size of the species examined. However, the correlation has only limited merit, because it is rather vague and there are many exceptions the shrew has values closer to those of the rat than to those of the mouse, for example, and the rabbit has values close to those of the guinea-pig.

A link between body size and cell size is an intriguing feature, and one that is observed only in a very few cell types in the body. While more observations will cast light on the nature of these links, the current data simply suggest that among the many factors influencing the muscle structure there is also the body size of the species and its relationship with the basic metabolic rate.

Recent studies have cast much doubt on the value of these relationships, centred on the notion of scaling, in all tissues in general A fifth conclusion is drawn by comparing mitochondria in different muscles from the same species. While along the gut of the guinea-pig variations in the chondrioma are small and probably of little significance and possibly, as usual, partly accounted for by technical variations , in contrast ileum and urinary bladder show a clear-cut difference.

In the rat the difference is even greater, with the bladder having only half the mitochondrial density than the ileum. The differential between gut and bladder is found both in guinea-pigs and in rats, while the differential between guinea-pigs and rats remains the same in the two organs. Such a large difference suggests the occurrence of a substantial difference in the energy access of the two muscles, by mitochondrial respiration and by anaerobic energy production via glycolysis.

In a parallel study 32 in the same segment of ileum used for the present work, the mitochondrial spatial density in the myenteric neurons was found to be about twice as large as that in the adjacent smooth muscle, and there was a similar differential between different mammalian species; in contrast, the corresponding enteric glial cells gave values similar to those of muscle cells, that is, much lower than those of the neurons.

The iris has the highest mitochondrial endowment of all smooth muscles, twice as large a chondrioma in the guinea-pig iris than in the bladder a very large difference was observed also in rats and rabbits, even without quantitative evaluations.

No explanation can be offered for this richness in mitochondria in the sphincter pupillae of the iris; in principle, it may be related to some of the unique features of that muscle, such as the high speed of contraction, the minimal external resistance to shortening or the intense exposure to light.

Visible light has marked effects on mitochondrial functions 33 , 34 ; whether this has any physiological significance for the musculature of the iris remains to be investigated. Age-related changes in the chondrioma are well known and rather extensive in some cell types, including skeletal muscle fibres 35 , 36 , Here only preliminary data are available, on the tenia coli of guinea-pigs, and they suggest only a minor reduction in aged animals except in case of extreme old age.

These data are difficult to interpret in view of the continuous changes in muscle cell size and shape, organelles, density of innervation, extracellular materials occurring in the tenia throughout life Mitochondria are highly dynamic organelles 39 , 40 , 41 and growth, fission, budding, change in shape are linked with the data presented here, yet not understood.

The relationship of mitochondria with the endoplasmic reticulum, well explored in preparations in vitro, is not clear in cells in situ , even in the case of smooth muscle cells where the movement of calcium between cytoplasmic compartments is essential in the control of contraction.

The links of mitochondria with microtubules and the cytoskeleton, crucial in a tissue capable of extensive isotonic contraction, should be explored, especially if detected in a whole tissue in conditions close to natural life. The Author declares that there is no conflict of interest with this work and the preparation of the paper. This paper is an excerpt from a presentation at the JSNR meeting in Nagoya, August , reviewing the contribution of morphology to our understanding of the autonomic nervous system, with special reference to smooth muscle cells.

National Center for Biotechnology Information , U. J Smooth Muscle Res. Published online Jul Giorgio Gabella 1. Author information Article notes Copyright and License information Disclaimer. University College London. Received May 24; Accepted Jun This article has been cited by other articles in PMC. Abstract The spatial density of mitochondria was studied by thin-section electron microscopy in smooth muscles of bladder, iris and gut in mice, rats, guinea-pigs and sheep.

Keywords: mooth muscle, muscle cells, mitochondria, morphometry, comparative quantitation. Introduction Mitochondria are well in evidence in all smooth muscle cells in every organ of the body; their role in aerobic metabolism is as well established as it is essential. Microscopy All the materials were dissected from freshly killed animals and, after a short passage in Krebs solution, were immersed in fixative, at room temperature. Morphometry The microscope images, in digital form, were analyzed with the software FreeHand version 10 and version MX both originally produced by Micromedia, but no longer supported by Adobe.

Open in a separate window. Ileal muscle of mouse A. Sheep In the circular muscle of the sheep ileum mitochondria in muscle cells appear uniformly distributed and are present, usually singly, in the large majority of cell profiles Fig.

Ileal muscle of sheep A. Table 1. Mitochondrial density in sheep ileum. Ileal muscle of guinea-pig A. Tenia coli In the tenia coli of young adult guinea-pigs 3 to 5 months of age mitochondria occupied about 3.

Table 2. Mitochondrial density in guinea-pig tenia coli. Guinea-pigs animal code Number of muscle cells Number of mitochondria Spatial density of mitochondria fetus, term BMT 83 2. Tenia coli of guinea-pig A. Bladder In the guinea-pig bladder detrusor muscle, muscle cells had mitochondria, which occupied 2.

Iris In the sphincter pupillae - the ring of usually entirely smooth musculature around the pupil - mitochondria were particularly abundant: in muscle cell profiles from 3 experiments there were 1, mitochondria occupying 9. Sphincter pupillae of guinea-pig A. Rat Ileum In the ileum of the rat, in muscle cell profiles of the circular muscle layer from 4 experiments 3, mitochondria occupied 6.

Ileal muscle of rat in four views A. Bladder In the urinary bladder detrusor muscle muscle cell profiles from 3 experiments contained 2, mitochondria, which occupy about 3. Detrusor muscle of bladder of rat A. Muscle cells of the detrusor muscle of rat bladder. Other animal species Data on other animal species were collected but were not sufficiently extensive for proper quantitation.

Rabbit In a large preparation of the ileum, muscle cell profiles of the circular layer contained 1, mitochondria, which occupied 4. Shrew In the shrew a small mammal with a body weight below 10 g , in a large preparation of the ileum muscle cell profiles of the circular layer contained 1, mitochondria, which occupied 5.

Amphibians, fishes, reptiles and birds Mitochondrial density in smooth muscles of amphibian was assessed in margin of the present study. Discussion The first concern to discuss is about the reliability of the procedures used, and their limitations.