[Morphology of glycogen. Electron microscopic study of the negative stains of particulate glycogen]

Rabbit skeletal muscle glycogen. A morphological and biochemical study of glycogen beta-particles isolated by the precipitation-centrifugation method

Glycogen in its particulate beta-form is localized in the sarcoplasm close to the sarcoplasmic reticulum. Some particles are in close contact with the membranes, on the outer side of the vesicles. The mild technique of differential precipitation-centrifugation has been adapted to the preparation of glycogen from adult skeletal muscle. A preliminary low-speed centrifugation which eliminates the contractile protein structures and the cell debris is followed by a high-speed centrifugation which produces pellets containing glycogen mixed with smooth-walled vesicles, the glycogen-sarcovesicular fraction. The glycogen obtained after treatment of this fraction with deoxycholate and two washings contains 3% protein. A similar protein content contaminates glycogen banded in a linear sucrose gradient. The glycogen-sarcovesicular fraction and the purified glycogen have been examined, under the electron microscope, in sections of fixed and embedded material or with the negative staining technique. The glycogen beta-particles in negatively stained preparations have an average diameter of 39.4 mmicro. The largest particles present irregular outlines, suggesting the presence of conglomerated subunits, about 20 mmicro in diameter. These subunits seem to fall apart under the influence of concentrated potassium hydroxide. The mean sedimentation coefficients calculated for infinite dilution vary from 115 to 135S. The spectrophotometric analysis of the glycogen-iodine complex indicates the presence of long end-chains in the molecule.

Studies on blood capillaries. I. General organization of blood capillaries in muscle

THE WALL OF THE BLOOD CAPILLARIES OF SKELETAL MUSCLES (DIAPHRAGM, TONGUE, HIND LEGS) AND MYOCARDIUM OF THE RAT, GUINEA PIG, AND HAMSTER CONSISTS OF THREE CONSECUTIVE LAYERS OR TUNICS: the endothelium (inner layer), the basement membrane with its associated pericytes (middle layer), and the adventitia (outer layer). The flattened cells of the endothelium have a characteristic, large population of cytoplasmic vesicles which, within the attenuated periphery of the cells, may attain a maximum frequency of 120/micro(2) of cell front and occupy approximately 18% of the cytoplasmic volume; these values decrease as the cells thicken toward the perikaryon. The vesicles are 650-750 A in over-all diameter and are bounded by typical unit membranes. They occur as single units or are fused to form short chains of two to three vesicles. Each configuration may lie entirely within the cytoplasm or open onto the cell surface. In the latter case, the unit membrane of the vesicle is continuous, layer by layer, with the plasmalemma. Chains of vesicles opening simultaneously on both the blood and tissue fronts of the endothelial tunic have not been observed either in sections or in a tridimensional reconstruction of a sector of endothelial cell cytoplasm. Adjacent endothelial cells are closely apposed to one another and appear to be joined over a large part of their margins, possibly over their entire perimeter, by narrow belts of membrane fusion (zonulae occludentes). Except for tongue capillaries, patent intercellular gaps are rare or absent. The middle layer is formed by a continuous basement membrane ( approximately 500 A thick) and by pericytes which lie in between leaflets of this membrane. The tips of the pericyte pseudopodia penetrate through the inner leaflet of the basement membrane and join the endothelium in maculae occludentes. The adventitia is a discontinuous layer comprising cellular (macrophages, fibroblasts, mast cells) and extracellular (fibrils, amorphous matrix) elements. The same general type of construction appears to be used along the entire length of the capillary.

Glycogen in human peripheral blood leukocytes. II. The macromolecular state of leukocyte glycogen

Glycogen of normal human blood leukocytes was studied in cell suspensions containing chiefly neutrophiles. In electron micrographs of neutrophiles stained with lead the glycogen particles appear to be relatively uniform with a diameter of 20 mmu. At high magnification the 20 mmu particle appears to be composed of at least eight subunits. Leukocyte glycogen released by lysis or homogenization sediments as a single peak of high molecular weight material. The great majority of the cell glycogen can be accounted for in the large molecular weight material. The large molecular weight material is degraded to small fragments by alpha-amylase and partially degraded by beta-amylase. Purification of cell glycogen by alkali extraction and ethanol precipitation produces a relatively uniform particle smaller than the original native macromolecule. Native glycogen was prepared in pure form by a sucrose density gradient technique and its purity demonstrated by its susceptibility to purified alpha-amylase and by analytical ultracentrifugation.

Ovarian steroid cells. I. Differentiation of the lutein cell from the granulosa follicle cell during the preovulatory stage and under the influence of exogenous gonadotrophins

The granulosa follicle cell of the Graafian follicle of the rabbit ovary differentiates into a lutein cell involved in steroid synthesis. Cytological events which occur within the granulosa cell of the normally stimulated follicle prior to ovulation have been duplicated by the intrafollicular injection of exogenous gonadotrophin. The luteinization of the granulosa cells involves the accumulation of 250- to 300-A, electron-opaque, spherical granules, dispersed within the cytoplasmic matrix, which have been identified as glycogen with the PAS-staining procedure. Further development of the granulosa cell following ovulation involves an increase in cell size, a decrease in the number of RNP particles, and an accumulation of an abundant system of intracellular membranes (agranular endoplasmic reticulum). Glycogen granules first appear in the granulosa cells as the separate, monoparticulate form. After follicle rupture and the formation of agranular endoplasmic reticulum, glycogen particles are present in a rosette arrangement within membrane-bounded vacuoles. The rosette arrangement of glycogen particles is also found dispersed within the cytoplasmic matrix of the lutein cell during the later stages of the cell life-span. Injection of luteinizing hormone or human chorionic gonadotrophin into a mature follicle also produces a marked accumulation of monoparticulate glycogen in the majority of granulosa cells, within 30 min. Cytoplasmic extensions which contain the glycogen masses are noticeably free of RNP particles.

Origin of granules in polymorphonuclear leukocytes. Two types derived from opposite faces of the Golgi complex in developing granulocytes

The origin, nature, and distribution of polymorphonuclear leukocyte (PMN) granules were investigated by examining developing granulocytes from normal rabbit bone marrow which had been fixed in glutaraldehyde and postfixed in OsO(4). Two distinct types of granules, azurophil and specific, were distinguished on the basis of their differences in size, density, and time and mode of origin. Both types are produced by the Golgi complex, but they are formed at different stages of maturation and originate from different faces of the Golgi complex. Azurophil granules are larger ( approximately 800 mmicro) and more dense. They are formed only during the progranulocyte stage and arise from the proximal or concave face of the Golgi complex by budding and subsequent aggregation of vacuoles with a dense core. Smaller ( approximately 500 mmicro), less dense specific granules are formed during the myelocyte stage; they arise from the distal or convex face of the Golgi complex by pinching-off and confluence of vesicles which have a finely granular content. Only azurophil granules are found in progranulocytes, but in mature PMN relatively few (10 to 20%) azurophils are seen and most (80 to 90%) of the granules present are of the specific type. The results indicate that inversion of the azurophil/specific granule ratio occurs during the myelocyte stage and is due to: (a) reduction of azurophil granules by multiple mitoses; (b) lack of new azurophil granule formation after the progranulocyte stage; and (c) continuing specific granule production. The findings demonstrate the existence of two distinct granule types in normal rabbit PMN and their separate origins from the Golgi complex. The implications of the observations are discussed in relationship to previous morphological and cytochemical studies on PMN granules and to such questions as the source of primary lysosomes and the concept of polarity within the Golgi complex.