RESUMO
We present a model describing the morphology as well as the assembly of "Terasaki ramps," the recently discovered helicoidal connections linking adjacent sheets of the rough endoplasmic reticulum (ER). The fundamental unit is a localized symmetric double-ramped "parking garage" formed by two separated gently pitched, approximately helicoidal, ramps of opposite chiralities. This geometry is stabilized by a short-range repulsive interaction between ramps associated with bending energy which opposes the long-range attraction associated with tension. The ramp inner boundaries are themselves stabilized by the condensation of membrane-shaping proteins along their length. A mechanism for parking garage self-assembly is proposed involving the nucleation of dipoles at the center of tubular three-way junctions within the smooth ER. Our predictions are compared with the experimental data.
Assuntos
Retículo Endoplasmático Rugoso/fisiologia , Retículo Endoplasmático Rugoso/ultraestrutura , Modelos BiológicosRESUMO
The chambers of the rete testis (RT) of guinea pig are lined by a simple epithelium, whose cells are squamous, cubical and columnar in shape. The epithelial cells with distinct shapes were counted and the quantitative analysis of the number of these cells showed relative predominance of cubical cells. The ultrastructural observations showed predominance of membrane interdigitations among the epithelial cells. These cells present common cytoplasmic organelles. The Golgi complex polarity is typical with observation of electronlucent vesicles on the Golgi cis face closely related to rough endoplasmic reticulum (ER) lamellae, mitochondria and large number of polysomes on the Golgi trans face. These related structures present in Golgi area of RT cells suggest secretory activity which maybe occurs in the RT epithelium. Endocytotic process also occurs in the RT and this function probably concerns the uptake of substances and resorption of seminiferous fluid. Apical cilia present in RT epithelium cells are related with fluid transport and perhaps with chemoreception. Presence of spermatozoa portions enclosed into the cytoplasm of some epithelium cells has been referred to as spermatophagy. The RT complex is mainly supported by loose connective tissue, with collagen fibres and some Leydig cells. Leydig cells are adjacent to the network channels of the septal part of the RT and apparently are able to secrete inside the RT lumen.
Assuntos
Células Epiteliais/ultraestrutura , Cobaias/anatomia & histologia , Organelas/ultraestrutura , Rede do Testículo/ultraestrutura , Animais , Tamanho Celular , Retículo Endoplasmático Rugoso/fisiologia , Retículo Endoplasmático Rugoso/ultraestrutura , Células Epiteliais/fisiologia , Complexo de Golgi/fisiologia , Complexo de Golgi/ultraestrutura , Masculino , Microscopia Eletrônica , Mitocôndrias/fisiologia , Mitocôndrias/ultraestrutura , Organelas/fisiologia , Rede do Testículo/fisiologiaRESUMO
The ultrastructure of the external gill epithelium of the axolotl, Ambystoma mexicanum, has been examined using conventional transmission electron microscopy to elucidate its role in ionic transport. Four cell types are identified in the gill filament and primary gill bar epithelium. These are granular, ciliated, Leydig and basal cells. A fifth cell type, the flat mitochondria-rich cell is only found in the gill bar epithelium. The predominant granular cells display microvilli at their surface and their cytoplasm contains abundant mitochondria, rough endoplasmic reticulum, Golgi complexes, vesicles and PAS+ secretory granules that are extruded at the surface, which along with secretions from the Leydig cells form a mucous coat. The granular cells are joined apically by junctional complexes consisting of zonulae occludens, zonulae adherens and desmosomes. The lateral membranes of granular cells enclose large intercellular spaces that are closed at the apical ends but remain open at the basal ends adjoining capillaries. In AgNO3-treated axolotl, the gills become darkly stained, the silver grains penetrate apical membranes and appear in the cytoplasm, accumulating near the lateral membranes and also enter the intercellular spaces. These findings are consistent with the dual role of the gill epithelium in mucus production and active ionic transport.
Assuntos
Ambystoma mexicanum/anatomia & histologia , Brânquias/ultraestrutura , Ambystoma mexicanum/fisiologia , Animais , Membrana Celular/fisiologia , Membrana Celular/ultraestrutura , Retículo Endoplasmático Rugoso/fisiologia , Retículo Endoplasmático Rugoso/ultraestrutura , Epitélio/fisiologia , Epitélio/ultraestrutura , Espaço Extracelular/fisiologia , Brânquias/fisiologia , Complexo de Golgi/fisiologia , Complexo de Golgi/ultraestrutura , Microvilosidades/fisiologia , Microvilosidades/ultraestrutura , Mitocôndrias/fisiologia , Mitocôndrias/ultraestruturaRESUMO
In the pituitary glands of lactating rats there is a striking proliferation of lactotropes during pregnancy and lactation. After the cessation of lactation, the population of lactotropes experiences an extensive programmed cell death of redundant cells until it reaches prepregnancy levels. The regressive changes occurring in lactotropes are autolytic in nature and usually these cells are engulfed by stellate cells. Other involuting lactotropes are mobilized toward the blood capillaries and some go into the capillary lumen for final disposal, presumably in the mononuclear phagocyte system. In this study we report a sequence of events occurring in regressing lactotropes, investigated by a systematic electron microscope analysis of the rat pituitary gland at different periods after interruption of lactation. Direct disposal of degenerating lactotropes and their cell remnants appears to be an alternative pathway for the clearance of the regressing cells that occur extensively among surplus lactotropes following ablactation.