Graduate Thesis Or Dissertation

The chick allantois : an ultrastructural and cytochemical study of an ion transporting epithelium

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  • Transporting epithelia have the ability to translocate ions and water from one side of the epithelium to the other against concentration and electrical gradients without disrupting the internal millieu of the cells. The pathway of ions and water across these epithelia is still a major unresolved question. The allantoic epithelium of the chick chorioallantoic membrane has the capability to transport ions and water. In this investigation employing ultrastructural and cytochemical techniques the ultrastructure of the chick allantoic epithelium of 15-18 day embryos is correlated to some of its functions. Transmission and scanning electron microscopy demonstrate the cellular heterogeneity of the allantoic epithelium which consists of three distinct cell types: (1) Granular cells: possess prominent apical granules and a few elongated basal processes which reach the basal lamina. (2) Mitochondria rich cells:contain abundant mitochondria and span the thickness of the epithelium. They comprise 10% of the luminal cells and are randomly distributed. (3) Basal cells: characterized by their relative paucity of cytoplasmic organelles, have no luminal exposure. The allantoic epithelium possesses all the characteristics of transporting epithelia and is structurally analogous to amphibian and reptilian urinary bladders. Carbonic anhydrase activity was localized exclusively in the mitochondria rich cells. Thus mitochondria rich cells might be involved in hydrogen ion transport. When acetazolamide, a potent inhibitor of carbonic anhydrase activity, is included in the incubation medium no reaction product is formed. The pyroantimonate-osmium tetroxide reaction was utilized for the localization of cations. Calcium chelation controls indicate that calcium is the cation precipitated by pyroantimonate. Different patterns of pyroantimonate deposition are found in each cell type. Basically, excluding nuclear deposits, the granular cells always have a large amount of deposits; the mitochondria rich cells have from none to moderate amounts; and the basal cells have none. In the granular cells deposits occur along the cytoplasmic side of the plasma membrane. Generally, the apical membrane has smaller deposits than the basolateral membranes. Depostis are also present in the intramembranous spaces of mitochondria, on the membranes of granules, and in the nuclei. In the mitochondria rich cells there are a few deposits on the inner plasma membrane surfaces, in the intramembranous spaces of mitochondria, and in the nuclei. Basal cells are devoid of deposits except in the nuclei. Calcium was also localized by fixation in glutaraldehyde-calcium. After fixation in glutaraldehyde plus 10 mM or 90 mM calcium chloride very faint electron opaque deposits are present along the cytoplasmic side of the entire plasma membranes of all the cell types. The apical membranes of the granular cells and the mitochondria rich cells have smaller deposits than the respective basolateral membranes. The deposits on the entire plasma membrane of the basal cells are also small. No deposits are present when calcium is absent, when 10 mM or 90 mM sodium chloride is used, or when osmium tetroxide is substitued for glutaraldehyde. When glutaraldehyde-calcium fixation is followed by pyroantimonate- osmium tetroxide postfixation, the pyroantimonate deposits follow the same pattern along the plasma membrane that the faint electron opaque deposits do in the glutaraldehyde-calcium fixation. In addition, scattered deposits are present throughout all the cell types. The mitochondria rich cells often have the most abundant deposits. The basal cells always have very few deposits. The physiological significance of calcium in the allantoic epithelium is speculative. The cytochemical results do suggest that each cell type possesses either a different physiological function or a variable degree of the same function.
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