Biomedical subjects
Publications and source records attributed to J W Ryan.
Replicas of fractured chromaffin cells are indicative of a range of activities thought to characterize exocytosis, including attachment of secretory vesicles to the plasma membrane, fusion, extrusion of contents, and membrane retrieval. Exocytosis sites are abundant on stimulated cells but are infrequent when calcium is omitted from the system.
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Pulmonary endothelial cells are capable of metabolizing a variety of circulating hormonal substances. Indirect evidence indicates that some of the relevant enzymes are located on the plasma membrane. The associated caveolae are of special interest as globular subunits, possibly enzyme clusters, are evident in their membranes. In the present study, freeze-etch techniques were used to improve understanding of the fine structure of endothelial cells and to extend our investigations of possible sites of enzymes capable of metabolizing circulating vasoactive agents. As in other cells studied by freeze-etching, intramembranous particles are found on both inner aspects of the plasma membrane. In undifferentiated areas of plasma membrane, the particles appear to have a random distribution. These areas fracture such that approximately equal proportions of the particles adhere to the cytoplasmic aspect of the outer leaflet and the extracellular aspect of the inner leaflet. However, the particles organize into rosettes and plaques at the base of caveolae, and, after fracture, the rosettes and plaques adhere predominantly to the cytoplasmic aspect of the outer leaflet. The peculiar organization of particles in association with caveolae supports the concept that caveolae have a stomal skeletal structure and raises the possibility that the organization may be in some way related to pinocytosis.
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(8-L-[(14)C] phenylalanine) angiotensin I is metabolized in one passage through blood-free lungs. Approximately 20 percent of the radioactivity emerges as angiotensin 11, the remainder as lower homologs. Radioactivity is not retained by the lungs but has the same volume of distribution and mean transit time as blue dextran, a compound unlikely to leave the intravascular space. Plasma membrane fractions of lung are capable of converting angiotensin I to angiotensin II. These data, taken together, indicate the circulating angiotensin I is metabolized by enzymes of the luminal surface of pulmonary endothelial cells.
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Scanning electron micrographs of the endothelium of the pulmonary artery reveal that the entire surface is covered by a meshwork of irregular projections which vastly increase the surface area. The size and density of the projections suggest that they may function to direct an eddying flow of plasma along the endothelial surface.
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1. The circular dichroism of bradykinin and a number of its analogues and homologues was measured over the spectral range 200-300nm. All of the biologically active peptides showed maxima at 220nm and minima at 235nm. The spectra were independent of solvent and temperature. The vibronic transitions of phenylalanyl residues in the 250-280nm range showed no evidence of intra- or inter-molecular interactions. We take this as evidence that bradykinin and its biologically active analogues and homologues exist in solution as disordered chains. 2. None of the analogues with spectra unlike bradykinin possessed biological activity. However, peptides such as retro-bradykinin, des-6-serine-bradykinin, des-1-arginine-bradykinin and des-9-arginine-bradykinin produced spectra like that of bradykinin but were devoid of biological activity. Although we could not identify spectral features that were clearly correlated with biological activity, it appears unlikely that highly ordered peptides of the same amino acid composition as bradykinin would possess bradykinin-like effects.
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