摘要:

In actively growing vitellogenic oocytes of Xenopus laevis mitochondria segregate into 2 populations. One stays around the nucleus, actively replicates mitochondrial DNA (mtDNA), and builds up most of the stock of the mitochondria in the full‐grown oocyte. The other moves toward the vegetal pole and stops replicating mtDNA early in vitellogenesis. Organelles of this population are components of the germ plasm of the cel

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1987.tb00549.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The 3‐dimensional structure of the Golgi apparatus has been analyzed in thin and thick sections of nonciliated epithelial cells of ductuli efferentes of rat by use of low‐ and high‐voltage electron microscopes and a stereoscopic approach. In thick sections of tissue impregnated with osmium, the Golgi apparatus appeared at low magnification as a continuous network forming a corona at the apical pole of the nucleus. At higher magnification and in thin sections of tissue postfixed with reduced osmium and stained with lead citrate or treated to demonstrate phosphatase activity, the following structural features were observed. In the longitudinal axis of the Golgi network there were alternating compact and noncompact zones. The compact zones were composed of 6‐8 flattened, poorly fenestrated saccules in close apposition to each other and forming stacks. The noncompact zones were composed of a number of highly fenestrated and slightly distended saccules, which were continuous with and bridged the saccules of the compact zones. In the cis‐trans axis of the Golgi apparatus the following compartments were observed: (a) On the cis face there was a continuous osmiophilic tubular network referred to as the cis element; (b) a cis compartment composed of 3 or 4 NADPase‐positive saccules perforated with pores in register forming wells that contained small vesicles; (c) a trans compartment composed of 1 or 2 TPPAse‐positive elements underlying the NADPase ones, followed by 1 or 2 CMPase‐positive elements that showed a flattened saccular part continuous with a network of anastomotic tubules. These tubular networks curved away from the overlying elements, giving these elements a “peeling‐off” configuration. These elements referred to as sacculotubular elements were discontinuous along the Golgi network. This compartment also included shriveled trans‐tubular networks detached from the overlying sacculotubular elements and seemingly undergoing fragmentation into vesicles and tubules. The structural features of the elements of the trans compartment were indicativ

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1987.tb00550.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Distribution of the muscarinic acetylcholine receptor on human fibroblasts was determined by immunofluorescence and immunoperoxidase staining using the anti‐muscarinic receptor antibody M‐35b. The receptor appeared to be randomly distributed on the cell surface in 1‐ or 2‐day nonconfluent cultures. Brief exposure to 0.1 mM carbamylcholine (15 min to 1 hr) induced receptor accumulation in several restricted domains of the cell surface. This process was associated with sequestration into uncoated vesicles. Random receptor distribution was restored by incubation in ligand‐free medium for 4 hr after carbamylcholine treatment, and vesicular profiles were no longer detectable. When incubation with the agonist was prolonged (3 hr at 37 degrees C), endocytotic ‘smooth vesicles’ fused and formed multivesicular structures presumably implicated in receptor down‐regulation. Conversely, when nonconfluent cells were exposed to the muscarinic antagonist atropine, receptor redistribution was revealed, leading to the formation of clusters where receptor accumulated. Muscarinic receptor redistribution induced by atropine therefore does not involve the sequestration process seen in carbamylcholin

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1987.tb00551.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Cultured arterial smooth muscle cells go through a transition from a contractile to a synthetic phenotype. Morphologically, the transition includes a reduction in size of the myofilament bundles and the formation of an extensive rough endoplasmic reticulum and a large Golgi complex. Functionally, it leads to loss of contractility, onset of cellular proliferation, and secretion of extracellular matrix components. This change in differentiated characteristics under in vitro conditions has attracted attention because of its resemblance to the modification of the smooth muscle cells that occurs in vivo during atherogenesis. Here, transmission electron microscopy and [3H]‐thymidine autoradiography were used to study the role of calcium ions in the control of phenotypic properties and growth of cultivated rat aortic smooth muscle cells. The calcium antagonist nisoldipine was found to lack distinct effect on the structural reorganization of the cells, but showed a moderate prohibitory effect on the start of DNA synthesis early in primary culture. In growth‐arrested secondary cultures, nisoldipine inhibited induction of DNA synthesis by serum or platelet‐derived growth factor (PDGF). The agent's effect was inversely related to the concentration of calcium ions in the extracellular medium and was partially counteracted by the calcium agonist BAY K 8644. In contrast, W‐7, an antagonist of the calcium‐binding protein calmodulin, potentiated the effect of nisoldipine and, at higher concentrations, inhibited induction of DNA synthesis in itself. The results suggest that the mitogenic stimulation of arterial smooth muscle cells involves a flux of calcium ions through the plasma membrane and requires participation of c

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1987.tb00552.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

There is increasing morphologic evidence that neuromuscular synapses are not rigid structures in the mature muscles of adult animals. On the contrary, they may be submitted to a continuous process of remodelling. In silver‐impregnated sternocleidomastoid muscles of the young adult rat, we measured synaptic parameters such as nerve terminal length, the number of branching points of terminal arborization, and muscle fiber diameter, and used a morphometric approach to explore specific questions concerning neuromuscular remodelling. Quantitative data indicate that: (a) The complexity and maturation of the nerve endings in this muscle are very variable and the increase in branching points is not paralleled by an increase in terminal length; (b) Muscle fiber diameter is related only marginally to presynaptic parameters; (c) Accessory ending formation occurs when the original ending does not reach the mean size of endings in singly innervated areas; (d) The complexity of individual endings at dually innervated junctions is smaller than the mean development of singly innervated synapses, indicating the existence of some mutual inhibitory influence between closely spaced endings. Morphometric results suggest a continuous process of synaptic formation in this adult muscl

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1987.tb00553.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

A new method has been developed for culturing 11‐day mouse forelimb buds in vitro. In cultures performed with conventional procedures, skeletal pieces frequently appeared distorted and reduced in size. Moreover, forelimb buds explanted from embryos younger than a stage corresponding to 50 pairs of somites developed narrow hand plates devoid of radiated autopods. By contrast, in the new procedure using media supplemented with fetal calf serum and growth factors and enhancing distal feeding with carrier implants of catgut, enlarged pads were obtained that exhibited at least 4 digital rays in buds explanted from embryos with 40‐44 pairs of somites. Compared with conventional procedures, the mean value of DNA content per limb bud was twice as great with use of our improved method. The ability of limb bud cells to proliferate and differentiate when cultured either in classical or in modified conditions, and the importance of the technical procedures, are discussed in the new prospect of in vitro developmental stud

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1987.tb00554.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY