Mitochondria in smooth muscle cells of viscera

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. Morphometric data included areas of muscle cell profiles (~6,000 muscle cells were measured) and areas of their mitochondria (more than three times as many). The visual method delivers accurate estimates of the extent of the chondrioma (the ensemble of mitochondria in a cell), measuring all and only the mitochondria in each muscle cell and no other cells. The digital records obtained can be used again for checks and new searches. Spatial density of mitochondria varies between about 2 and 10% in different muscles in different species. In contrast, there is consistency of mitochondrial density within a given muscle in a given species. For each muscle in each species there is a characteristic mitochondrial density with modest variation between experiments. On the basis of data from serial sections in the rat detrusor muscle, mitochondrial density varies very little between the muscle cells, each cell having a value close to that for the whole muscle. Mitochondrial density is different in a given muscle, e.g., ileal circular muscle, from the four mammalian species, with highest values in mouse and lowest in sheep; in mice the mitochondrial density is nearly three time higher that in sheep. In a given species there are characteristic variations between different muscles. For example, the bladder detrusor muscle has markedly fewer mitochondria than the ileum, and the iris has markedly more.

Muscle cells, nerves, fibroblasts and vessels in the detrusor of the rat urinary bladder

“…In the montages prepared for morphometry, the mitochondria were traced digitally and their number, size (sectional area) and overall volume obtained. In muscle cells mitochondria occupy 3.13% of the sectional area of muscle cells (2,155 mitochondria in 419 muscle cell profiles from 3 animals; the average in each animal is 3.24%, 3.04% and 3.16%), in line with the results already published (7). Mitochondrial spatial density varies greatly between individual cell profiles, and some profiles have no mitochondria.…”

“…The current data and those in the literature (7) obtained with the same method, confirm the quantitative differences in the chondrioma in different smooth muscles of the same species. For example, gut muscle cells (in the ileal circular muscle) have about 30% more mitochondria than the bladder ones.…”

“…The morphometric method has produced a reliable estimate of the extent of the chondrioma, that is the spatial density of mitochondria in muscle cells. The merit of microscopy in the evaluation of the chondrioma, in addition to more popular biochemical methods, has been discussed elsewhere (7). According to these results, when measurements are carried out on sufficiently large samples, the extent of the chondrioma in muscle cells: i. it is the same in different individuals; ii.…”