LUMENating blood vessels

The acquisition of a lumen is an essential step in vascular morphogenesis. In this issue of Developmental Cell, Xu et?al. (2011) show that the small GTPase Rasip is a critical regulator of cytoskeleton dynamics and cell adhesion, which together drive the emergence of vascular lumens.     

The fine structure of cephalopod blood vessels

Summary The fine structure of blood vessels of the retina and arms of Octopus and the lip of Sepia is described.There are two main types of vessels. The first type (type 1) has a complete basement membrane, an incomplete lining of endothelial cells formed into finger—like processes, and a complete investment of pericytes surrounding the vessel. These latter cells contain myofilaments. The second type (type 2) is smaller and contains few if any myofilaments, and has a less complexly folded endothelium. This type is subdivided into three forms depending on the number of pericytes and the form of the endothelial lining.Amoebocytes are described and these form a distinct group of cells.The fine structure of hemocyanin is observed in normally fixed material and is correlated with its previously described structure.These observations are related to their possible functional importance.

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Zusammenfassung Die Ultrastruktur von Blutgefäßen der Retina und der Arme von Octopus und der Lippe von Sepia wird beschrieben.Es bestehen vorwiegend zwei Gefäßtypen. Der erste Typ (Typ 1) zeigt eine geschlossene Basalmembran, eine unvollständige Begrenzung durch Endothelzellen, die fingerförmige Fortsätze bilden und eine vollständige Pericytenhülle um das Gefäß. Die letztere enthält Myofilamente. Der zweite Typ (Typ 2) ist kleiner und enthält wenig oder keine Myofilamente. Er besitzt ein weniger komplex gefaltetes Endothel. Dieser Typ wird gemäß der Zahl der Pericyten und der Form der endothelialen Begrenzung in drei Gruppen unterteilt.Deutlich verschiedene Amoebozyten werden beschrieben.Die Ultrastruktur von Haemocyanin ist an normal fixiertem Material zu beobachten. Sie wird zu ihrer in früheren Arbeiten beschriebenen Struktur in Beziehung gebracht.Die Beobachtungen werden in Hinblick auf ihre mögliche funktionelle Bedeutung diskutiert.

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Acknowledgements. We would like to acknowledge the encouragement and advice of Professor J. Z. Young and Dr. E. G. Gray. Mrs. J. I. Astafiev did the drawings and Mr. A. Aldrich and Mr. S. Waterman helped with the photography.     

Potassium and blood vessels.

Intraarterial infusion of potassium causes vasodilation whereas reduction of the potassium concentration in the inflowing blood causes vasoconstriction. These responses have always been puzzling since the predicted effects from the Nernst equation are just the reverse. Recent evidence suggests that they result form effects on the activity of sarcolemmal Na, K ATPase in the vascular smooth muscle cell which influence the electrogenic NaK pump. The possible relevance of these findings is discussed.     

The fine structure of cephalopod blood vessels II. The vessels of the nervous system

Summary Blood vessels of the perioesophageal nerve ganglia (brain) of Octopus vulgaris and the stellate ganglia of Sepia officinalis are described. The vessels have an incomplete endothelium, a complete basement membrane and a complete investment of pericytes. The pericytes are joined by specialised membrane junctions but these are not tight junctions. The main type of neuron/vessel arrangement is one where there is a collagen-filled space between the pericytes and the surrounding glial cells. Axons or neurons are sometimes applied directly to the vessel pericytes and in the neuropil, pericytes contact glial cells that ensheath bundles of axons. Blood spaces between neurons are also present.We would like thank Professor J. Z. Young and Dr. E. G. Gray for encouragement and advice, Mrs. Jane Astafiev for drawing Fig. 11, Mr. S. Waterman for photographic assistance and Miss Cheryl Martin for secretarial and other assistance.     

The effect of VEGF on blood vessels and blood cells during Xenopus development

Vascular endothelial growth factor (VEGF) is known to play an essential role in vascular development. We have overexpressed VEGF122 or VEGF170, which are equivalent to mouse VEGF120 and VEGF164, in developing Xenopus embryos. Overexpression of VEGF170 but not VEGF122 demonstrated an absence of expression of hematopoietic markers alpha-globin and GATA-1 but only in the posterior portion of the blood island. Interestingly, strong signals of endothelial markers, msr, fli-1, and tie-2, were detectable in those regions, instead of hematopoietic markers. These results suggested both that injection of VEGF170 resulted in disturbance of vasculogenesis in the posterior portion of the blood island, with excessive production of endothelial cells at the expense of blood cells, and that the anterior and posterior portions of the VBI may have distinct characteristics.     

The collagen of the gingiva and of its blood vessels

The collagen of the gingiva and that of its blood vessels of several animal species and of man were studied with the scanning electron microscope following corrosion with pancreatin at 0.3%. The gingival collagen forms fundamental cells or fasciculi that are distributed throughout the entire territory. In the interior of the cells there are small balls either detached or in clusters. Because of the contact and the fusion of these balls with the collagenic fasciculi, and due to their resistance to the pancreatin corrosion procedure, we believe them to be condensations of collagen. The approximate size of these balls was 2 micrometer. The fasciculi that surround these cells have either the form of bundles or are united in bands. There is an abundance of blood vessels in the gingiva and they are surrounded by collagen. This collagen can assume any of varied positions. The relations that exist between the vascular collagen and that of the gingiva are different in every case.     

Cryopreservation of isolated blood vessels

Canine saphenous veins were immersed in fetal calf serum (FCS) containing various cryoprotective agents, slowly frozen and stored for several weeks at subzero temperatures. Pharmacological investigations of frozen/thawed tissues revealed considerable attenuation of the contractile force of frozen stored veins as compared to unfrozen veins. The best recovery after thawing of frozen stored canine veins was obtained on tissues which had been frozen slowly to -70 degrees C and stored in liquid nitrogen while being immersed in FCS containing 1.8 mol/l dimethyl sulfoxide (DMSO). Though the maximum response to noradranline of helical strips prepared from these veins was diminished to about 60% the evidence suggests that there may be a very good preservation of the main biochemical properties, such as monoamine oxidase activity, endogenous prostaglandin synthesis and neuronal uptake mechanism in veins stored under these conditions. The same method of cryopreservation was applied to store samples of human veins. Comparison of the pD2 values for various agonists and of the blocking activities of various antagonists of both 5-HT receptors and alpha-adrenoceptors yielded an excellent correlation between the parameters determined on frozen/thawed and unfrozen human veins. It is concluded that freezing isolated blood vessels may be considered an effective means of preserving and storing vascular tissues for pharmacological investigations.