The role of mucopolysaccharides in vesicle architecture and endothelial transport. An electron microscope study of myocardial blood vessels

Liquid water intake of the lone star tick, Amblyomma americanum: Implications for tick survival and management

Ixodid ticks are ectoparasites that feed exclusively on blood as their source of nutrients. Although ticks spend most of their life off the host, until now it has been assumed that the blood and the water vapor are the only sources of water to maintain water balance and prevent desiccation. Here we report for the first time that adult lone star ticks, Amblyomma americanum, also actively drink nutrient-free water, which greatly increases their survival. The volume of ingested water is greater in females than males (0.55 ± 0.06 vs 0.44 ± 0.07 µl) and most likely due to differences in tick size. Water uptake occurs through mouthparts and it can be later observed in the salivary glands and the midgut. We also exploited this behavior by adding a variety of inorganic compounds and microorganisms to water. Addition of inorganic salts to drinking water such as KH2PO4 + NaCl+KNO3 resulted in 100% tick mortality within 3 days. As a proof of concept for using the water drinking as a delivery route of toxic reagents for ticks, we also show that adding Pseudomonas aeruginosa to drinking water quickly leads to tick death. This tick behavior can be exploited to target important physiological systems, which would make ticks vulnerable to dehydration and microbial dysbiosis.

Quasi-periodic substructure in the microvessel endothelial glycocalyx: a possible explanation for molecular filtering?

The luminal surface of endothelial cells is lined with the glycocalyx, a network structure of glycoproteins probably 50 to 100 nm thick. It has been suggested that a relatively regular fibre-matrix structure may be responsible for the ultrafiltration properties of microvascular walls, both when the endothelium is continuous and when it is fenestrated. Positive structural evidence demonstrating an underlying periodicity in the glycocalyx has been hard to obtain. Here we present structural analysis of glycocalyx samples prepared in a variety of ways for electron microscopy. Using computed autocorrelation functions and Fourier transforms of representative areas of the electron micrograph images, we show that there is an underlying three-dimensional fibrous meshwork within the glycocalyx with characteristic spacings of about 20 nm. Together with a fibre diameter consistent with our observations of about 10-12 nm, the 20-nm spacing provides just the size regime to account satisfactorily for the observed molecular filtering; the observations are consistent with the fibre matrix model. We also show that the fibrous elements may occur in clusters with a common intercluster spacing of about 100 nm and speculate that this may reveal organisation of the glycocalyx by a quasi-regular submembranous cytoskeletal scaffold.

Structural determinants of glomerular permeability

Recent progress in relating the functional properties of the glomerular capillary wall to its unique structure is reviewed. The fenestrated endothelium, glomerular basement membrane (GBM), and epithelial filtration slits form a series arrangement in which the flow diverges as it enters the GBM from the fenestrae and converges again at the filtration slits. A hydrodynamic model that combines morphometric findings with water flow data in isolated GBM has predicted overall hydraulic permeabilities that are consistent with measurements in vivo. The resistance of the GBM to water flow, which accounts for roughly half that of the capillary wall, is strongly dependent on the extent to which the GBM surfaces are blocked by cells. The spatial frequency of filtration slits is predicted to be a very important determinant of the overall hydraulic permeability, in keeping with observations in several glomerular diseases in humans. Whereas the hydraulic resistances of the cell layers and GBM are additive, the overall sieving coefficient for a macromolecule (its concentration in Bowman's space divided by that in plasma) is the product of the sieving coefficients for the individual layers. Models for macromolecule filtration reveal that the individual sieving coefficients are influenced by one another and by the filtrate velocity, requiring great care in extrapolating in vitro observations to the living animal. The size selectivity of the glomerular capillary has been shown to be determined largely by the cellular layers, rather than the GBM. Controversial findings concerning glomerular charge selectivity are reviewed, and it is concluded that there is good evidence for a role of charge in restricting the transmural movement of albumin. Also discussed is an effect of albumin that has received little attention, namely, its tendency to increase the sieving coefficients of test macromolecules via steric interactions. Among the unresolved issues are the specific contributions of the endothelial glycocalyx and epithelial slit diaphragm to the overall hydraulic resistance and macromolecule selectivity and the nanostructural basis for the observed permeability properties of the GBM.

Identification of distinct luminal domains for macromolecules, erythrocytes, and leukocytes within mammalian capillaries

A thick endothelial surface coat consisting of the glycocalyx and associated plasma proteins has been hypothesized to reduce functional capillary volume available for flowing plasma macromolecules and blood cells. The purpose of this study was to compare anatomic and functional capillary diameters available for macromolecules, RBCs, and WBCs in hamster cremaster muscle capillaries. Bright-field and fluorescence microscopy provided similar estimates (mean +/- SE) of the anatomic capillary diameter: 5.1 +/- 0.1 microns (bright field, 39 capillaries in 10 animals) and 5.1 +/- 0.2 microns (membrane dye PKH26, 18 capillaries in 2 animals). Estimates of functional diameters were obtained by measuring the width of RBCs and WBCs and the intracapillary distribution of systemically injected fluorescein isothiocyanate (FITC)-dextran 70. WBCs (5.1 +/- 0.2 microns) fully occupied the anatomic capillary cross section. In contrast, the widths of RBCs (3.9 +/- 0.2 microns, 21 capillaries in 8 animals) and FITC-dextran (4.3 +/- 0.2 microns, 21 capillaries in 8 animals) were significantly smaller than the anatomic capillary diameter. Continuous (1- to 5-minute) excitation of fluorochromes in the capillary lumen (light-dye treatment) increased the width of RBCs passing the treated site from 3.6 +/- 0.3 to 4.4 +/- 0.3 microns (6 capillaries in 4 animals) and the width of the FITC-dextran column from 4.1 +/- 0.2 to 4.6 +/- 0.3 microns (10 capillaries in 7 animals). Furthermore, light-dye treatment increased capillary tube hematocrit by 60% in 40-microns-long capillary segments compared with untreated sites in the same capillaries. It is concluded that the wall of skeletal muscle capillaries is decorated with a 0.4- to 0.5-microns-thick endothelial surface coat, which may represent the true active interface between blood and the capillary wall.

Relationship between microvascular permeability and ultrastructure

This article attempts to review some of the advances made during the past few years in our understanding of the nature of the barrier presented by the endothelial cell wall and how it may contribute to the regulation of exchange between blood and tissues. It has concentrated on a small number of experimental techniques which have yielded information on the correlation between structure and function of the endothelial cell wall and which have emphasized the potentially dynamic characteristics of the barrier. Whilst there now seems to be little dispute as to the location of the fluid conducting channels across the endothelial cell wall, within the clefts, fenestrae and in inflammation the open cell junctions, it has proved difficult to identify the molecular filter which limits macromolecular exchange across these pathways. In fenestrated endothelium it has been suggested that the filter resides at the fenestral diaphragms or in the underlying basement membrane, while in continuous endothelium there is strong support in the literature that the filter is located within the intercellular cleft, at regions of closely apposed cell membranes, or in the case of a vesicular pathway, at the necks or diaphragms of the vesicle openings. Alternatively, there is a considerable and increasing body of experimental evidence that macromolecular movement is retarded by the endothelial cell coat which lines the whole of the endothelial cell surface and covers the openings of interendothelial cell clefts, fenestral diaphragms and vesicle openings. It is believed to comprise glycoproteins secreted and regulated by the endothelial cells themselves and to have associated with it plasma proteins, particularly serum albumin. Expression of this glycocalyx and its modification have been demonstrated in vivo and in cultures of isolated endothelial cells, in vitro. Experiments using single microvessels in which a correlation between structure and function can be most readily made, offer further evidence that the clefts between endothelial cells are quantitively more than sufficient in extent to accommodate the fluid fluxes measured in even the most highly permeable vessels. They further demonstrate that the dramatic increases in fluid flux seen in inflammation result from a modulation of endothelial cell shape to form interendothelial cell gaps by activation of intracellular contractile mechanisms, mediated by changes in intracellular calcium. Increases in macromolecular leakage may only be seen when gap formation is accompanied by extensive modulation of the intercellular cement substance, or glycocalyx filling those gaps.(ABSTRACT TRUNCATED AT 400 WORDS)

Cationic dyes reveal proteoglycans structurally integrated within the characteristic lesions of Alzheimer's disease

The cationic dyes ruthenium red (RR) and cuprolinic blue (CB) were used to preserve proteoglycans (PGs) for visualization at the ultrastructural level in brain tissue from seven cases of Alzheimer's disease (obtained at autopsy within 3-4 h after death). PGs were visualized as RR-positive granules specifically localized to the amyloid fibrils in neuritic plaques. In neurofibrillary tangles, RR granules were localized to the paired helical filaments and straight filaments usually at a consistent periodicity of 40-70 nm. CB, known to preserve PGs as short punctate filaments, also demonstrated PGs specifically localized to the amyloid fibrils in neuritic plaques and in association with paired helical filaments and straight filaments in neurofibrillary tangles. Persistent staining with CB at magnesium chloride concentrations of 0.3 and 0.7 M in the neuritic plaques suggested the presence of highly sulfated PGs, whereas abolishment of CB staining at 0.7 M magnesium chloride in the neurofibrillary tangles implied that different PGs and/or glycosaminoglycans were present in the neurofibrillary tangles. The specific ultrastructural localization of PGs to the characteristic lesions in Alzheimer's disease suggests that PGs are part of a complex structural network with amyloid fibrils in neuritic plaques and the filamentous structures present in neurofibrillary tangles.

Freeze-fracture analysis of endothelial cell membranes in rabbit carotid arteries subjected to short-term atherogenic stimuli

Endothelial cell membranes of rabbit carotid arteries were examined by the freeze-fracture technique. In the normal endothelium the mean densities of membrane-bound vesicles were 75 vesicles/microns 2 on the luminal cell membrane and 102 vesicles/microns 2 on the abluminal membrane. Whilst the vesical openings on the luminal membrane were randomly distributed those on the abluminal membrane were typically ordered in a macular pattern with lines free of vesicles. Tight and gap junctions between endothelial cells were numerous. After stimulating the carotid arteries with weak electrical impulses, a technique used to induce enhanced endothelial permeability and the formation of atheromatous plaques after repeated stimulations (Betz et al. 1985), vesicle openings were reduced to 78 vesicles/microns 2 on abluminal membranes. Membranes on the luminal side and intercellular tight and gap junctions remained unchanged.

Capillary permeability and how it may change

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Antidiuretic hormone response in the amphibian urinary bladder: time course of cytochalasin-induced vacuole formation, an ultrastructural study employing ruthenium red

Cytochalasin is known to inhibit the antidiuretic hormone-induced hydro-osmotic response (bulk water flow) in the amphibian urinary bladder without altering hormone-stimulated diffusional water permeability or short-circuit current. In addition, histological studies have shown that the mold metabolite induces the formation of large intracellular vacuoles or lakes in the epithelial cells. We report here a transmission electron microscopic time-course study which indicates that during the early phases of the ADH response cytochalasin causes the formation of numerous multivesicular bodies or aggregates derived from individual basolateral pinocytotic vesicles. Because of their apparent hypertonic nature, the vesicles, as well as the vesicular aggregates, accumulate water during hormone-stimulated hydro-osmotic flow. As a result, the multivesicular bodies dilate and fuse to form the large intracellular lakes characteristic of cytochalasin treatment in the presence of both an applied osmotic gradient and vasopressin. In the presence of mucosal ruthenium red, the luminal glycocalyx was heavily stained with this tracer. At no time, however, even in the presence of hormone, was there any evidence for the uptake of this dye at the apical epithelial border. In the presence of serosal ruthenium red, the lateral intercellular spaces, basolateral pinocytotic vesicles, basal lamina, and collagen, as well as other subepithelial structures, were ruthenium positive. With cytochalasin D, vasopressin, and serosal ruthenium red, both the pinocytotic vesicles and the multivesicular bodies demonstrated an apparent membrane associated ruthenium positive coat. The tracer data indicates that the basolateral pinocytotic vesicles, increased by the presence of hormone, are indeed endocytotic in nature. The mucopolysaccharide coat associated with these structures may be involved in ionic and/or fluid transport.

Effect of plasma proteins on endothelial binding and vesicle loading of anionized ferritin in rabbit aorta

Endothelial binding and vesicle loading of anionized ferritin (AF, isoelectric point, 3.8 to 4.2) in plasma and in Tyrode's solution were investigated in the rabbit aorta. After 2 minutes of in situ perfusion, binding to vesicle necks was significantly higher than elsewhere on the membrane and was independent of AF concentration in the range of 0.05 g/ml to 0.2 g/ml for both perfusates. After 30 minutes, no particles were seen in abluminal vesicles and few had reached the basement membrane. Compared to AF in plasma, AF in Tyrode's solution showed lower endothelial binding and greater vesicle loading (p less than 0.005). The average number of particles per loaded vesicle was equal to the average particle density at vesicle necks in Tyrode's solution, but not in plasma, for 0.1 g/ml AF. Gel chromatography and electrophoresis demonstrated no detectable difference between AF particles incubated in plasma or Tyrode's solution. Our experiments indicate that adherence to, or entrapment in, the glycocalyx is an important step for molecules that are transported by vesicles. We hypothesize that plasma proteins adsorb to the endothelial surface and partially shield its net negative charge so that more AF may bind. Plasma proteins also inhibit vesicle loading either sterically or by modifying the electrical potential at the vesicle neck compared to that within the vesicle cavity.

Exchange area and surface properties of the microvasculature of the rabbit submandibular gland following duct ligation

The exchange area of the submandibular salivary gland microvasculature has been measured to allow the value of microvascular permeability (P) to hydrophilic solutes to be calculated from previous measurements of permeability-surface area (PS) products. Glands whose ducts had been ligated for 2 weeks and the contralateral control glands were perfusion-fixed with a modified Karnovsky's fixative after perfusion with a solution containing cationized ferritin, and examined with transmission electron microscopy. Stereological techniques were used to estimate the surface area of the exchange vessels on random thin sections from four control and four duct-ligated glands. The mean exchange surface area in control glands was 512 cm2 g-1 and 336 cm2 g-1 in duct-ligated glands. The fenestral density was calculated to be 0.57% of the exchange surface in control glands and 0.30% in duct-ligated tissue. Molecules of cationized ferritin appeared bound to the luminal surface of the microvascular endothelium, including the surface of the fenestrae to a depth of about 25 nm in both control and ligated glands. These experiments have shown that the exchange surface area of the fenestrated endothelium of the submandibular salivary gland is comparable to that in cardiac muscle but the permeability (P) to small solutes is about 10 times greater. Following ligation of the salivary gland duct, solute permeability falls and an explanation of this, based on the reduced surface area and the nature of the permeability-flow relationship for small solutes is offered.

Endothelial transport of anionized and cationized ferritin in the rabbit thoracic aorta and vasa vasorum

Transport of anionized ferritins (AF,pl = 3.8-4.2), weakly cationized ferritins (WCF, pI = 7.8-8.1) and cationized ferritins (CF, pI greater than 9.0) was investigated in the rabbit aorta and vasa vasorum. After a 2-minute in situ perfusion, all ferritin species entered luminal vesicles and bound to the luminal endothelial membrane with a high surface density at vesicle necks and regions of cell overlap. In comparison to the aorta, the vasa vasorum had a higher surface density for AF, lower surface densities for CF and WCF, and fewer vesicles containing CF, WCF, or AF. In both types of vessels, vesicle loading of all ferritin species did not agree with a Poisson distribution. After perfusion times of up to 30 minutes, no abluminal vesicles or vasa vasorum endothelium contained CF or WCF; a few abluminal vesicles near cell borders contained AF. In the vasa vasorum, CF and AF entered the subendothelium via occasional fenestrae; AF, but not CF, also permeated the adventitia. Our findings indicate that: 1) binding sites for oppositely charged particles coexist in the same microdomains; 2) the glycocalyces of the vasa vasorum and aorta differ in their relative affinities for oppositely charged particles; 3) vesicular labeling with ferritin is not solely diffusive; and 4) vesicles do not traverse the aortic endothelium under these experimental conditions.

Endothelial cell coat modifications in rat thoracic aorta. Effect of ovariectomy and cigarette smoke

The effects of acute cigarette smoking and bilateral ovariectomy on the thickness of rat aortic cell coat (Con A) were investigated. Ovariectomized rats showed a significant increase in the thickness of the cell coat. When cigarette smoking was combined with ovariectomy the thickness of the reaction product was similar to controls. Cigarette smoke without ovariectomy resulted in a decreased thickness, but these changes were not significant.

The steady-state transport of cationized ferritin by endothelial cell vesicles

1. The steady-state transfer of cationized ferritin by endothelial cell vesicles has been investigated quantitatively using electron microscopy. Single capillaries from the mesenteries of decerebrated frogs were perfused in vivo with solutions containing 3-5 g 100 ml(-1) cationized ferritin or cationized ferritin (3-5 g 100 ml(-1)) and bovine albumin (1 g 100 ml(-1)). Perfusions lasted between 60 and 240 s, at which time the tissues were fixed in situ with osmium tetroxide.2. Measurements of the free diffusion co-efficient of cationized ferritin in the presence and absence of 1 g 100 ml(-1) albumin (0.400+/-0.09 x 10(-6) cm(2) s(-1) and 0.361+/-0.08 x 10(-6) cm(2) s(-1), respectively) were not significantly different which suggests that albumin does not bind to cationized ferritin. Together they yielded a value for the Stokes-Einstein radius of cationized ferritin of 5.59 nm, which was not significantly different from that of native ferritin.3. Examination of transverse sections of perfused capillaries showed a layer of cationized ferritin molecules (> 26 nm thick) close to the luminal surface of the endothelial cell wall, in both the presence and absence of albumin. Estimates of the concentration of cationized ferritin within the layer showed it to be approximately twice that of the perfusate concentration, confirming that cationized ferritin binds and concentrates at the cell surface.4. When no albumin was present in the cationized ferritin perfusate, all the luminal vesicles (those open to the luminal cell surface) were labelled with molecules of cationized ferritin. The mean number of ferritin molecules per labelled luminal vesicle (F/N(L)) was 5.0+/-0.7, a value close to that predicted from the concentration of cationized ferritin in the layer if it was assumed that the whole of the vesicle volume was available to molecules of cationized ferritin, i.e. that cationized ferritin could penetrate the cell coat lining the vesicles as it does that covering the luminal cell surface.5. Few cytoplasmic vesicles (0.26+/-0.04) and abluminal vesicles (0.07+/-0.03) were labelled with cationized ferritin in the absence of albumin. The mean number of cationized ferritin molecules per labelled vesicle in both vesicle populations was also low. In addition, labelled cytoplasmic vesicles F/N(L) = 1.87+/-0.33) always contained significantly fewer ferritin molecules than labelled luminal vesicles (F/N(L) = 5.0+/-0.7). These findings offer further support for the fusion model of the steady-state transfer of ferritin by endothelial cell vesicles (Clough & Michel, 1981) and are not consistent with the translocation of labelled luminal vesicles across the cell. They also suggest that cationized ferritin binds to the cell coat lining the vesicles, and is unavailable for transfer during transient fusions between vesicles.6. The presence of albumin in the cationized ferritin perfusate reduced the fractional labelling of all three vesicle populations to one third of their values in its absence. It also reduced the mean number of ferritin molecules per labelled vesicle at all three sites in the cell. It is suggested that albumin reduces the volume of distribution of cationized ferritin within the vesicles either by competing with cationized ferritin for the same binding sites within the cell coat, or by simply occupying space within the extracellular matrix.

Proteoglycans in the microvasculature. I. Histochemical localization in microvessels of the rabbit eye

The ultrastructural organization of ruthenium red (RR) stainable material within small blood vessels located in the limbus of the rabbit eye was studied. Proteoglycans were identified in this material by digesting tissues with Streptomyces hyaluronidase, testicular hyaluronidase, chondroitinase ABC, or heparinase before ruthenium red staining. Neuraminidase digestion enabled separate identification of sialoglycoprotein. The luminal surface of endothelial cells demonstrates an RR-stained glycocalyx containing both sialoglycoprotein and proteoglycans, which are removed by testicular hyaluronidase and crude heparinase. The basal coat of endothelial cells and small granules (10-20 nm in diameter) located within the basal lamina stain with RR and are removed only by crude heparinase. The surface coat of smooth muscle cells and small granules (10-20 nm) within their basal laminas are also digested by crude heparinase. Large proteoglycan granules (20-50 nm), which are completely removed by testicular hyaluronidase and partially digested by Streptomyces hyaluronidase, are deposited between the connective tissue fibers of the media and adventitia. Other large granules that are attached to collagen fibers contain enzyme-resistant anionic materials. The surface coat of adventitial fibroblasts is removed only by crude heparinase. Thin filaments (3-5 nm in diameter) interconnect the cell coat material, basal lamina granules, and large connective tissue granules, to form a network of proteoglycans that traverses the intima, media, and adventitia. The highly ordered arrangement of proteoglycans in the microvascular wall suggests that these macromolecules play several roles in microvascular function.

The role of vesicles in the transport of ferritin through frog endothelium

1. The transport of ferritin molecules by endothelial cell vesicles has been quantitatively investigated by electron microscopy. Single mesenteric capillaries of pithed frogs were perfused with solutions containing 6.7 g ferritin 100 ml.-1 for known periods before fixation in situ with osmium tetroxide. 2. Two series of experiments were carried out: in the first series the perfusate contained bovine serum albumin (1.0 g 100 ml.-1); in the second series the perfusate contained no protein other than the ferritin. To assess the molecular radius of ferritin in solution, the free diffusion coefficient of ferritin was measured in the presence and absence of albumin. 3. The free diffusion coefficient of ferritin in saline solution (110 m-mole 1.-1) was found to be 0.35 X 10(-6) cm2 sec-1 at 21 degrees C and was not affected by the presence of bovine serum albumin. This indicates that there is no significant binding of albumin to ferritin in solution and yields a value for the Stokes-Einstein radius of ferritin of 6.1 nm. 4. In all perfusion experiments the percentage of luminal vesicles containing ferritin exceeded the percentage of labelled cytoplasmic vesicles, which in turn exceeded the percentage of labelled abluminal vesicles. 5. Labelling of all vesicle populations was seen after perfusions lasting less than 1 sec. At this time luminal vesicles were more heavily labelled in the absence of albumin. 6. The labelling of luminal vesicles increased with lengthening perfusion times up to 30-40 sec, after which steady levels of labelling were achieved. The rate of rise in luminal labelling and the steady-state levels reached were both greater in the absence of albumin. By contrast cytoplasmic labelling increased above its initial value only after perfusions of longer than 10 sec. 7. In the steady state, labelled cytoplasmic vesicles contained, on average, fewer ferritin molecules than labelled luminal vesicles. This finding is inconsistent with translocation of labelled luminal vesicles across the cell. 8. It is suggested that the early constant labelling of cytoplasmic and abluminal vesicles is consistent with the existence of vesicular channels. Later cytoplasmic labelling may result from the transient fusion of cytoplasmic vesicles with labelled luminal vesicles for periods long enough to allow mixing of vesicular contents. Albumin may affect vesicular transport by its interaction with the endothelial glycocalyx.

An ultrastructural study on the ear cartilage of rabbits after the administration of papain. Appearance of cross-striated collagen segments of an atypical FLS-type

Crude papain was administered intravenously to young rabbits and the cartilage of the collapsed ear was examined electron-microscopically. Degeneration and recovery of chondrocytes, and decrease in and recovery of the electron-density of elastic fibers, were observed during the collapse and restoration of the ear. Some samples were stained with ruthenium red. In the collapsed ear, with a marked decrease of proteoglycan in the cartilage, loss of ruthenium red-positive granules was observed in the extracellular matrix. Collagen fibrils in the cartilage appeared to be somewhat increased in number, some of their diameters became slightly greater, and a part were assembled into bundles, occasionally accompanied by periodic cross-striation. Decrease of proteoglycan in the cartilage matrix probably brought about the unmasking and the assembly of collagen fibrils. In one of the experimental animals, collagen fibrous segments of an atypical fibrous long spacing (FLS-)type with symmetrical cross-striation were found around the chondrocytes in the ear cartilage, during the period of recovery. Some kind of the endogenous sulfated carbohydrate may have acted to affect the arrangement of type II collagen or procollagen molecules newly produced by the recovering chondrocytes.

The evolution of vascular changes in the spontaneously hypertensive rat

A longitudinal study on the development of vascular lesions was carried out in the spontaneously hypertensive rat (SHR) of the Aoki-Okamoto strain. The aorta and intrarenal arterial vessels were examined at different ages, from 5 to 48 weeks, by light and electron microscopy. Endothelial permeability to injected horseradish peroxidase (HRP) was evaluated in 20-week-old animals. Morphologic differences between vessels of SHRs and age-matched normotensive controls (Wistar-Kyoto strain) were first noted at 10 weeks of age and became more pronounced with time. Vascular pathology involved both intima and media. Medial thickening was seen in both aorta and peripheral arteries and, in the latter, was associated with decreased luminal diameters. These medial changes may contribute to the maintenance of the elevated blood pressure. Intimal lesions affected predominantly the aorta and were characterized by an expansion of the subendothelial space with deposition of acid mucopolysaccharides. There was increased accumulation of tracer HRP in the expanded subendothelium, which suggested enhanced permeability and/or retention of the tracer. In animal species susceptible to atherosclerosis, these intimal changes could serve as the structural basis for the higher propensity for atheromatous lesions in hypertensive individuals. In the SHR, despite stabilization of systolic blood pressure at about 20 weeks of age, both intimal and medial lesions continue to progress and become more extensive and severe; this suggests that not only the severity of hypertension but also its duration are significant determinants of the degree of vascular damage.

The labelling of vesicles in frog endothelial cells with ferritin

1. The labelling of endothelial cell vesicles with ferritin has been investigated by electron microscopy. Single capillaries in the frog mesentery have been perfused with solutions of known concentrations of ferritin for known periods before fixing the tissue in situ by superfusion with osmium tetroxide. 2. At 17 degrees C, the percentage of lumenal vesicles labelled with ferritin increased as the period of perfusion was increased up to 16 sec prior to fixation. When perfusions were longer than 16 sec, the percentage of vesicles labelled with ferritin remained fairly constant at 70%. 3. At 3 degrees C, no more than 25% of the lumenal vesicles were labelled during the first 30 sec. 4. After correcting the data for losses of ferritin due to sectioning, the distribution of ferritin molecules in the lumenal vesicles was consistent with a Poisson distribution. 5. After perfusions of 16 sec or longer, the number of ferritin molecules per labelled vesicle was roughly three to four times less than would be predicted from the lumenal concentration. 6. At all times there was a gradient of vesicles labelled with ferritin across the endothelial cells, i.e. the percentage of lumenal vesicles labelled was greater than that for cytoplasmic vesicles which in turn was greater than that for vesicles at the ablumenal surface. 7. Whereas the labelling of lumenal vesicles from zero time up to 16-20 sec, the main increase in labelling of cytoplasmic vesicles occurred between 10 and 20 sec. 8. It is concluded that there is a major diffusion barrier to ferritin molecules either close to the endothelial cell surface or across the necks of the lumenal vesicles. It also appears that ferritin molecules do not have access to vesicles during the latter part of their residence at the lumenal surface.

The role of extracellular material in chick neurulation. II. Surface morphology of neuroepithelial cells during neural fold fusion

Changes in cell surface morphology of the neuroepithelium during fusion of neural folds in the chick were studied. As the folds were about to meet, a thick extracellular coat material (ECM) appeared between the two leading edges. Cell membranes forming the fusion area were relatively smooth and heavily coated with ECM. By contrast, the apical surface of most cells lining the wall of the neural tube was folded with much less ECM. During the contact of neural folds, ECM was displaced from the space between the two leading edges, leaving a thin, closely adherent "typical" cell surface coat. Trypsin and concanavalin A inhibited proper alignment and fusion of apposing neural folds by modifying the surface of developing neuroepithelium. Results of this study support a hypothesis that ECM may serve temporarily as an adhesive to bind together the leading edges of neural folds until establishment of more intimate contacts (junctional complexes).

Endothelial cell morphology in areas of in vivo Evans blue uptake in the aorta of young pigs. II. Ultrastructure of the intima in areas of differing permeability to proteins

The fine structure of the intima of the pig aortic arch is described for areas of spontaneously differing in vivo endothelial permeability, as demarcated by uptake of the protein-binding azo dye Evans blue. Areas of enhanced permeability (blue areas) consistently show a variety of features not observed in areas devoid of dye accumulation (white areas). The subendothelial space of blue areas is markedly thickened and edematous, containing collagen, elastic tissue elements, and undifferentiated cells dispersed in an amorphous floccular matrix of low electron density. Endothelial cells in blue areas are generally cuboidal, with relatively short, frequently vacuolated junctions. In contrast, endothelial cells from white areas are flat and elongate, with long intercellular junctions exhibiting many interdigitations. Cytoplasmic differences include a well-developed rough endoplasmic reticulum and more frequent lysosomal bodies in blue areas and a prominent Golgi apparatus in the endothelium of white areas. Additionally, endothelial cell injury or death with and without denudation occurs with a significantly greater frequency in blue relative to white areas. An endothelial glycocalyx is some threefold thicker over the surface of white relative to blue areas. It is concluded that neither endothelial structure nor function are homogeneous within the aortic arch of the young pig and that areas of spontaneously differing permeability to proteins are associated with a spectrum of alterations in endothelial and intimal morphology.

Pressure effects on the distribution of extracellular materials in the rhesus monkey outflow apparatus

An electron-microscopic investigation was conducted to determine the distribution of extracellular materials in the rhesus monkey outflow apparatus at various maintained levels of intraocular pressure. Intraocular pressure was maintained at either 0,8, 15, 22, 30, or 50 mm Hg, by an intracameral needle attached to a reservoir system for a period of 1 h. Thereafter the eyes were fixed either by intracameral perfusion of glutaraldehyde at the appropriate pressure level, or by carotid perfusion of the fixative, or by rapid enucleation and immersion fixation. The electron-dense cationic stains, colloidal thorium and colloidal iron were used to indicate the presence of carbohydrate-rich extracellular materials in the drainage tissues. In the control tissue (15 mm Hg), heavy concentrations of stain were detected within the cores of the trabeculae and in the extracellular spaces of the endothelial meshwork. With pressure elevation there was a progressive decrease in the surface staining on the meshwork cells, an increase in staining intensity within the trabecular cores, and a 'washout' of extracellular materials from the spaces of the endothelial meshwork. The washout was thought to occur via giant vacuoles up to 30 mm Hg, but at 50 mm Hg the process was accelerated by loss of association between the cells of the canal endothelial monolayer. Over the entire pressure range 0 to 50 mm Hg, there was an increase in the staining on the apical surface of the canal endothelium which was associated with a decrease in the incidence of micropinosomes.

Quantitative electron microscopic study of capillaries in diabetes mellitus

A systematic microscopic examination of all elements of the capillary wall was performed on quadriceps muscle biopsies from 9 diabetic patients and 8 controls. The capillary basement membrane (CBM) was markedly thicker in diabetics; it consisted of several lamellae and contained large vacuoles which were never observed in non-diabetic subjects. Large magnifications revealed fibrils in greater number and markedly larger in diameter in diabetics, these accounting for a considerable volume of the CBM and the adventitia and increased diameter and thickness of the capillary wall, without encroaching on the lumen. The intracellular fibrils in pericytes and endothelial cells were also larger and thicker in diabetic subjects. The prevalence of fibrillar material in the vascular disease of diabetes mellitus suggests the importance of research into possible measures to arrest fibril formation.

Proteoglycans in primate arteries. I. Ultrastructural localization and distribution in the intima

Proteoglycans were identified and localized histochemically and ultrastructurally in normal and hyperplastic arterial intimas in nonhuman primates (Macaca nemestrina). These regions were consistently more alcianophilic than the adjacent medial layers and this alcianophilia was absent after treatment with glycosaminoglycan-degradative enzymes. Ultrastructurally, the intimal intercellular matrix consisted of numerous, irregularly shaped, 200-500-A diameter granules possessing 30--60-A diameter filamentous projections, and these granules were dispersed between collagen and elastic fibers. The granules exhibited a marked affinity for ruthenium red and were interconnected via their filamentous projections. The ruthenium red-positive granules were intimately associated with the plasma membrane of intimal smooth muscle cells and attached to collagen fibrils and elastic fibers. The matrix granules were completely removed after testicular hyaluronidase or chondroitinase ABC digestion but only partially removed after leech hyaluronidase treatment. These results suggest that the matrix granules contain some hyaluronic acid and one or more isomers of chondroitin sulfate. In addition to the large ruthenium red-positive matrix granules, a smaller class of ruthenium red-positive granule (100--200-A diameter) was present within the basement membranes beneath the endothelium and surrounding the smooth muscle cells. Ruthenium red also exhibited an affinity for the surface coat of the smooth muscle cells. The potential importance of proteoglycans in arterial intimal hyperplasia is discussed.

Pressure-induced changes in the ultrastructure of the endothelium lining Schlemm's canal

In a transmission electron microscopic investigation of the endothelium lining Schlemm's canal subjected to graded levels of intraocular pressure (0 to 50 mm Hg for one hour), there was an increase in the number of vacuolar structures with the increase in pressure (range, 8 to 30 mm Hg). At 0 mm Hg, giant vacuoles were absent, while at 50 mm Hg their numbers were less than at 22 and 30 mm Hg. Vacuoles were invaginations either from the meshwork or from the canal surface of the endothelium. A few were transcellular channels that possibly served as a pressure-sensitive outflow system. In addition, the numbers of nonvacuolar transcellular channels and minipores increased with an increase in pressure while the numbers of pinocytotic and micropinocytotic vesicles decreased. The changes were not accompanied by alterations in organelles associated either with protein or energy production. At 50 mm Hg, breaches in the endothelium lining the trabecular wall were obvious and aqueous outflow was considered to be by nonphysiologic routes.

The permeability of muscle capillaries to horseradish peroxidase

The main objective of this study was to determine the pathways by which horseradish peroxidase (HRP) can cross the endothelium of muscle capillaries. Specimens of mouse diaphragm were fixed for cytochemical analysis at various intervals after intervenous injection of 0.5 mg HRP, at 4 min after intervenous injection of varied amounts of HRP, and at 4 min after intervenous injections in various volumes of isotonic NaCl. Our findings indicate that endothelial junctions serve as a barrier which may allow passage of very limited amounts of HRP. They also suggest that endothelial vesicles transfer HRP from the capillary lumen to the pericapillary interstitium as well as in the reverse direction. Increasing the volume of solution injected to approximately 30% of total blood volume did not increase the amount of HRP that left the capillary lumen. Our results with HRP do not provide clearcut evidence that endothelial junctions are the site of the small pore.

Interstitial pulmonary edema following bromocarbamide intoxication

Bromocarbamides are sleep-inducing drugs which can lead, in man, to intoxication and death due to respiratory failure. To prove whether hemodynamic factors or the changed endothelial permeability induce pulmonary edema, animal experiments were performed. The fine structural changes in pulmonary edema in rabbits were observed at 60, 90 and 120 minutes after oral administration. The major findings were a) large blebs between capillary endothelium and alveolar epithelium and b) interstitial edema of the vessel wall. The bleb contents were much less electron dense than the blood contents in the capillary. Colloidal carbon did not enter the bleb or the edematous interstitial tissue. Exogenous peroxidase uptake in pinocytotie vesicles increased in pathologic cases. The hemodynamic measurements in animal receiving artificial respiration which maintained the blood pO(2) at a steady state showed similar blebs in the pulmonary vessels, indicating that anoxia is not the major cause of the vascular lesion. Moreover, pulmonary arterial pressure and pulmonary vascular resistance could be held in the normal range in artificially respirated animals under bromocarbamide intoxication. Thus, hemodynamic factors are not likely to play a pathogenetic role in bringing about pulmonary edema. The chief, early factor is the increased endothelial permeability due to increased cytoplasmic transport. From this a practical suggestion for treating patients with bromocarbamide intoxication is derived: the usual fluid replacement in shock patients should be handled with great care to avoid fluid overload of the lung.

Permeability of muscle capillaries to exogenous myoglobin

Whale skeletal muscle myoglobin (mol wt 17,800; molecular dimensions 25 x 34 x 42 A) was used as a probe molecule for the pore systems of muscle capillaries. Diaphragms of Wistar-Furth rats were fixed in situ at intervals up to 4 h after the intravenous injection of the tracer, and myoglobin was localized in the tissue by a peroxidase reaction. Gel filtration of plasma samples proved that myoglobin molecules remained in circulation in native monomeric form. At 30-35 s postinjection, the tracer marked approximately 75% of the plasmalemmal vesicles on the blood front of the endothelium, 15% of those located inside and none of those on the tissue front. At 45 s, the labeling of vesicles in the inner group reached 60% but remained nil for those on the tissue front. Marked vesicles appeared on the latter past 45 s and their frequency increased to approximately 80% by 60-75 s, concomitantly with the appearance of myoglobin in the pericapillary spaces. Significant regional heterogeneity in initial labeling was found in the different segments of the endothelium (i.e., perinuclear cytoplasm, organelle region, cell periphery, and parajunctional zone). Up to 60 s, the intercellular junctions and spaces of the endothelium were free of myoglobin reaction product; thereafter, the latter was detected in the distal part of the intercellular spaces in concentration generally equal to or lower than that prevailing in the adjacent pericapillary space. The findings indicate that myoglobin molecules cross the endothelium of muscle capillaries primarily via plasmalemmal vesicles. Since a molecule of this size is supposed to exit through both pore systems, our results confirm the earlier conclusion that the plasmalemmal vesicles represent the large pore system; in addition, they suggest that the same structures are, at least in part, the structural equivalent of the small pore system of this type of capillaries.

Biochemical characterization and cytochemical localization of a catecholamine-sensitive adenylate cyclase in isolated capillary endothelium

Capillaries were isolated from epididymal fat, and a catecholamine-sensitive adenylate cyclase found in these capillaries was characterized. The effect of various hormones on the accumulation of adenosine 3':5'-cyclic monophosphate in capillary endothelial cells was determined and the cyclase was found to exhibit mixed alpha and beta characteristics. Cyclase was cytochemically localized in these endothelial cells with 5'-adenylyl-imidodiphosphate as a specific cyclase substrate and alloxan as a specific cyclase inhibitor. Lead imidodiphosphate was precipitated at or near the site of cyclase activity upon hydrolysis of 5'-adenylyl-imidodiphosphate by cyclase. This reaction product was observed primarily on the luminal surface of intact capillaries, in micropinocytic invaginations, in free vesicles within the cytoplasm, and in the intracellular junctions.