The Fine Structure of Tissue Mast Cells in Triturus pyrrhogaster (Boie)

Abstract

The iris of adult Triturus pyrrhogaster (BOIE) was fixed with either phosphate buffer with sucrose added, or chrom osmium fixative of DALTON and embedded in methacrylate. One part was electron stained. As a control, thick sections embedded in methacrylate were stained for light microscopy, or regular light microscopic sections fixed in CARNOY's fluid were stained with thionine or metyl-green pyronin.
The cell body is filled with specific granules which have a cross section that is round, oval, or spindle shape. The nuclear substance, which generally is of high electron density, frequently is compressed and demonstrate an irregular contour corresponding to the location of the specific granules so that a characteristic appearance is presented.
There are specific granules that have a limiting membrane, in others the limiting membrane is partially absent while in some the limiting membrane is competely absent. The specific granules consist of a matrix and a middle disk. The matrix has varying electron density and is composed of ill defined particles that are distributed in various density and a pale homogenous substance. The ‘middle disk’ is of high electron density and usually appears to be an irregular shape disk. There are cells that appear dark electron microscopically in which most of the granules have a matrix of high electron density (tentatively termed dark cells) and cells that appear light under the electron microscope in which most of the granules have matrix of low electron density (termed light cells) as well as cells that are intermediate between these two types. The cells may also be classified into large granule type cells in which the matrix of the granule usually measures less than 2.5μ in long diameter with a middle disk which is less than 2μ in long diameter, and small granule type cells in which the long diameter of the matrix is less than about 1.5μ with a middle disk that is less than about 1.2μ in long diameter.
On the surface of the middle disks is a linear lamellar structure consisting of alternate layers of electron dense zones 40-50Å in width and slightly wider zones of low electron density. In the latter layer are seen vacuoles. The separation of the middle disk, which was seen, is thought to be the result of expansion of these vacuoles and pictures which were felt to represent the course of this process were seen. This process of separation of the middle disk was illustrated in the diagram. There also are cells in which the granules have a middle disk which is very thin or even absent while in other cells granules may be seen in which the middle disk have a much decreased electron density with disappearance of the lamellar structure so that the middle disk appears as a swollen homogenous solid. The author feels that the dark and light cells represent different phases of the functional cycle of a single type of cell and that the morphological variability of the fine structure of the granules is due to the many different substances that are produced by the granules.
The intergranular substance generally is scanty and contain a small number of mitochondria, GOLGI's substance and endoplasmic reticulum. Occasionally seen within the matrix of specific granules are small bodies with a vesicular or canalicular structure which resemble swollen mitochondria and the close relation between the specific granules and mitochondria was suggested.