Diogenes of Apollonia: a pioneer in vascular anatomy.

Diogenes of Apollonia was a pre-Socratic philosopher who lived in the 5th century BC and provided the first systematic and fairly truthful account of blood vessel architecture in man. This article presents Diogenes' report and comments on the most significant passages of his vascular description. It also discusses the magnitude of Diogenes' contribution to shape early theories regarding blood vessel physiology. What emerges from this portrait is the figure of an eclectic spirit, who remarkably influenced the development of leading concepts in vascular anatomy and biology.

The fluorescent probe Bodipy-FL-verapamil is a substrate for both P-glycoprotein and multidrug resistance-related protein (MRP)-1.

Several fluorescent probes have been used in functional studies to analyze drug transport in multidrug-resistant cells by fluorescent microscopy. Because many of these molecules have some drawbacks, such as toxicity, nonspecific background, or accumulation in mitochondria, new fluorescent compounds have been proposed as more useful tools. Among these substances, Bodipy-FL-Verapamil, a fluorescent conjugate of the drug efflux blocker verapamil, has been used to study P-glycoprotein activity in different cell types. In this study we tested by fluorescent microscopy the accumulation of Bodipy-FL-Verapamil in cell lines that overexpress either P-glycoprotein (P-gp) or multidrug resistance-related protein 1 (MRP1). Expression of P-gp and MRP1 was evaluated at the mRNA level by RT-PCR technique and at the protein level by flow cytometric analysis using C219 and MRP-m6 monoclonal antibodies. Results indicate that Bodipy-FL-Verapamil is actually a substrate for both proteins. As a consequence, any conclusion about P-gp activity obtained by the use of Bodipy-FL-Verapamil as fluorescent tracer should be interpreted with caution.

Piecemeal degranulation as a general secretory mechanism?

In this article we review the ultrastructural findings, functional aspects, and biological significance of piecemeal degranulation (PMD), a unique secretory pathway that has been described in basophils, mast cells, and eosinophils. Recent ultrastructural data suggestive of PMD in enteroendocrine cells of the gastrointestinal tract and chromaffin cells of the adrenal medulla are also presented and discussed. Further research on PMD in secretory cells of the endocrine and exocrine glands, as well as in neurons, is recommended, since the current data indicate that PMD has a broader spectrum of expression than was hitherto reported. The identification of the PMD phenotype in different cell types (e.g., basophils, mast cells, eosinophils, enteroendocrine cells, and adrenal chromaffin cells) suggests that PMD is a unique degranulation model for paracrine and endocrine secretion. Further investigation will clarify whether PMD can be considered as a general mechanism for the slow release of bioactive stored materials by granulated secretory cells.

The mast cell: a multifunctional effector cell.

Mast cells (MC) are recognized key cells of type I hypersensitivity reactions. Several lines of evidence, however, indicate that MC not only express critical effector functions in classic IgE-associated allergic disorders, but also play important roles in host defence against parasites, bacteria and perhaps even viruses. Indeed, it is now clear that MC can contribute to host defence in the context of either acquired or innate immune responses through the release of a myriad of pro-inflammatory and immunoregulatory molecules and the expression of a wide spectrum of surface receptors for cytokines and chemokines. Moreover, there is growing evidence that MC exert distinct nonimmunological functions, playing a relevant role in tissue homeostasis, remodeling and fibrosis as well as in the processes of tissue angiogenesis. In this review, we provide a small insight into the biology of mast cells and their potential implications in human pathology.

Recombinant human alpha-2a interferon promotes an atypical process of mast cell secretion with ultrastructural features suggestive for piecemeal degranulation.

Purified mast cells (MC), isolated from the rat peritoneum, were stimulated in vitro with recombinant human IFN-alpha 2a (rhIFN-alpha 2a) and studied ultrastructurally. Quantitative determination of histamine release was also performed. The following ultrastructural features were observed: (1) dilation of single granules, leading to the formation of cytoplasmic cavities filled with dissolved or eroded matrices; (2) induction of partially empty, nonfused granule containers close to unaltered resting granules, a process very suggestive of piecemeal degranulation; (3) focal exocytosis, characterized by opening of single granules to the cell exterior and/or fusion of a few granules into small secretory channels. Histamine release was slightly increased in rhIFN-alpha 2a-treated MC, although not to significant levels. These results indicate that rhIFN-alpha 2a induces a characteristic pattern of degranulation in rat peritoneal MC and that a small proportion of rhIFN-alpha 2a-stimulated MC shows ultrastructural features suggestive for piecemeal degranulation.

Granule changes of human and murine endocrine cells in the gastrointestinal epithelia are characteristic of piecemeal degranulation.

Piecemeal degranulation is a unique pattern of cell secretion that consists of a slow release of granule contents from cytoplasmic secretory granules, which leaves empty chambers that do not fuse with each other or with the plasma membrane. To our knowledge, no cell types other than mast cells, basophils, and eosinophils have been reported in the literature to show morphological features of piecemeal degranulation. In the present study we provide evidence for ultrastructural morphologies characteristic of piecemeal degranulation in entero-endocrine cells of the human and murine gastrointestinal epithelia. Human biopsy samples were taken from the mucosa of the distal duodenum, proximal jejunum, and colon in 10 patients undergoing endoscopic examination for malabsorption, diarrhea, and/or abdominal pain. Murine gastrointestinal samples were obtained from 10 adult C57 mice. All specimens were prepared for transmission electron microscopy (TEM) according to standard protocols. Results showed that different types of gastrointestinal entero-endocrine cells, in both humans and mice, were recognizable with ultrastructural features diagnostic for piecemeal degranulation, including specific granule and cytoplasmic changes. In the granules, the content was found to be loosely packed or diminished. Notably, altered granules did not fuse with each other or with the plasma membrane, and were characteristically intermingled with normal, resting granules. At times, the release events transformed the granules into enlarged, empty containers. Numerous entero-endocrine cells presented a rich supply of membrane-bound vesicles (50-200 nm in diameter) that were free in the cytoplasm or attached to granules. This finding of piecemeal degranulation in gastrointestinal entero-endocrine cells suggests that such a secretory model might be a general degranulation pattern in cells involved in paracrine-endocrine secretion.