Myosin in cultured human endothelial cells

Thrombin-induced shape changes of cultured endothelial cells: metabolic and functional observations

Cultured human umbilical vein endothelial cells (EC) incubated in the presence of 2-deoxy-D-glucose (20 mmol/l) or at 4 degrees C lost their ability to undergo shape changes when exposed to thrombin (1 N.I.H. u/ml). Drugs blocking Ca++-flux (verapamil and nifedipin), microfilament disrupting agents (cytochalasin B and D) and microtubule disrupting agents (colchicine and colcemid) did not prevent thrombin-induced shape changes. None of the agents tested inhibited the accelerated thrombin-induced 51Cr-release from the cells. Pretreatment of EC with thrombin did not influence their ability to mediate clot retraction.

Effects of thrombin on the integrity of monolayers of cultured human endothelial cells

51Cr-prelabelled endothelial cells (EC) in confluent monolayers were incubated in RPMI 1640 + foetal calf serum 20% (v/v) to which purified thrombin was added. Thrombin (greater than or equal to 0.1 NIH U/ml) significantly accelerated 51Cr-release and caused extensive but reversible cell "contraction". Thrombin-exposed EC reacted to a new dose of thrombin with no appreciable shape change, but 51Cr-efflux was again accelerated. EC exposed to thrombin pretreated with N-bromosuccinimide (modifying the macromolecular site) or phenylmethylsulfonyl fluoride (blocking the serine site) retained normal morphology and did not leak excess amounts of 51Cr. Antithrombin III also inhibited the effect of thrombin. Pretreatment of EC with either indomethacin, aspirin, sulfinpyrazone, pronase or neuraminidase did not influence the effect of subsequent thrombin exposure.

Ultrastructure of the human dermal microcirculation. III. The vessels in the mid- and lower dermis and subcutaneous fat

This paper describes the ultrastructure of the microcirculatory vessels in the mid- and lower dermis and subcutaneous fat. Reconstruction of vessel walls, tracing out the courses of individual vessels, and survey examination of vessels were carried out by various combinations of routine and serial, ultrathin, and 1-micron sections. Intracellular myofilamentous bundles associated with extracellular filaments were a characteristic feature of the endothelial cells in arterioles possessing an internal elastic lamina, but were only rarely seen in endothelial cells of venules. The ultrastructural features of these bundles and filaments suggested both contractile and anchoring functions. The elastic lamina of the arterioles was shown to be composed of individual elastic fibers oriented in the long axis of the blood vessel under the endothelium, rather than being a continuous sheet as in larger arteries and arterioles. The capillaries in the fat had walls of normal thickness (0.1-0.3 micron) similar to capillaries in other organs, in contrast to the dermal capillaries whose walls are 2-3 micron thick. The arterioles, capillaries, and venules in the fat were frequently devoid of veil cells in contrast to those in the dermis. Venous capillaries with bridged fenestrations were found in close proximity to eccrine sweat glands and hair bulbs in the forearm, trunk, and buttock skin.

Human megakaryocytes. I. Characterization of the membrane and cytoplasmic components of isolated marrow megakaryocytes

Human marrow megakaryocytes have been isolated with high purity and yield by processing marrow cells sequentially through density centrifugation and velocity sedimentation. Analysis of the isolated cells for various platelet-associated components by immunofluorescence demonstrated that fibrinogen, plasma factor VIII antigen (factor VIII:AGN) platelet myosin, platelet glycoproteins I and III are present on the membrane and in the cytoplasm of over 90% of marrow megakaryocytes. Parallel studies of human and mouse megakaryocytes and platelets for IgG receptor (FcR), complement receptor type one (CR1) (C3b receptor), complement receptor type two (CR2) (C3d receptor), and Ia antigen by fluorescence and (or) rosette formation methods were performed. FcR were present on most human megakaryocytes and platelets. The Ia antigen was detected on a proportion (10-15%) of human megakaryocytes but it was undetectable on human platelets. CR1 was found on 20-40% of mouse megakaryocytes and also on a proportion of mouse platelets. These differentiation markers may be of use in monitoring megakaryocyte maturation.

Cellular angiomas of infancy: an ultrastructural study of two cases

Vascular tumors in infants may be clinically disfiguring, requiring surgical intervention. Some of these lesions are histopathologically worrisome, due to increased cellularity and mitotic activity. The interpretation of these lesions is hampered by a surfeit of terminology, although, regardless of the diagnostic name, they are clinically benign. Two such cellular angiomas are reported, one typical and one unusual case. Electron microscopy of both cases demonstrated a heterogeneous cellular composition, primarily endothelial cells and pericytes. In those light microscopic areas of diffuse growth, primitive vascular structures were resolved. Electron microscopy may be diagnostically useful in supporting the light microscopic impression of a vascular tumor.