Ultrastructural transition from the elastic to the muscular arteries

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The distribution of actin filaments (AFs) in the endothelial cells was compared between in the aorta (elastic artery) and in the intrarenal arteries (muscular artery). In the adult rats, the distributional patterns of endothelial AFs in these arterial segments were almost identical. On the contrary, AFs in the aortic endothelial cells were shown to be reorganized from the stress fibers at birth to the peripheral bands in the adult. The subendothelial basement membranes of the intrarenal arteries showed the ultrastructural heterogeneity along the course of the arterial tree.For the comparison of the medial ultrastructure between elastic and muscular arteries, we studied the intrapulmonary arteries, where the transition of the two types of arteries could be traced within the lung. It was revealed that the transition occurs abruptly in the lung without any intermediary segment. An immunocytochemical study on the myosin heavy chain isoforms revealed a molecular heterogeneity between the renal glomerular afferent and efferent arterioles.An exhaustive morphometric study revealed that, during postnatal development of the rat kidney, the glomerular volume increased mainly through the elongation of capillaries, and the elongation was accompanied by expansion of glomerular basement membranes (GBM). Electron microscopy showed that "GBM-outpockets", where GBM are thought to be expanded, were distributed chiefly in the periphery of the glomeruli.The cytoskeletons in the renal glomerular podocyte was studied in experimental models. In the isolated perfused kidneys, the glomerular filtration barrier was shown to be extensible and the cytoskeletons in the podocyte was thought to counteract against the excessive extension. In the Masugi-nephritis rats, retraction of the foot processes of the podocytes was accompanied by the reorganization of AFs, and these AFs seem to prevent of the detachment of podocytes from GBM.