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J A Firth

Publications and source records attributed to J A Firth.

At least 37 records · Page 2Linked to original sources
PubMed1992

Interendothelial junctions during blood-brain barrier development in the rat: morphological changes at the level of individual tight junctional contacts.

The endothelium of brain capillaries represents the structural basis for the blood-brain barrier in vertebrates. Individual endothelial cells are linked by a continuous belt of complex tight junctions (zonulae occludentes). Hydrophilic solutes and macromolecules are believed to cross the barrier through specific carrier mechanisms. Unspecific paracellular ionic leak is thought to be very low. In rats the blood-brain barrier is not fully developed until postnatal day 24. We investigated the ultrastructure of the developing blood-brain barrier at 5 developmental stages between embryonic day 17 and young adults. The use of high power goniometric tilting of ultrathin sections allows one to gather information about the exact relationship between two opposing membranes throughout the entire length of the cleft. Our results suggest that the maturation of blood--brain barrier interendothelial clefts is accompanied by the establishment of a characteristic ratio of 'narrow zone' (complex tight junctions) to 'wide zone' (15-20 nm), and of a typical cleft length. Membrane separation larger than 20 nm disappear and individual tight junctional contacts undergo structural changes.

Animals↗
PubMed1992

Fine structure of the paracellular junctions of terminal villous capillaries in the perfused human placenta.

Selected lobules of human term placentae were extracorporeally perfused for a recovery period of 20 min, fixed by perfusion and mordanted with ferrocyanide prior to processing for transmission electron microscopy. The lateral membranes of the endothelial cells of the terminal villous capillaries were found to be separated by paracellular clefts of mean width 15.6 nm. At tight junctional regions (1-4 sites per cleft) the two membranes approached each other more closely and frequently appeared to fuse. However, tilting of the sections in the electron microscope stage showed that the membranes were separated by a gap of mean width 4.1 nm in at least 94% of tight junctional profiles. When individual tight junctions were studied by a combination of serial sectioning and goniometric tilting, they were seen to widen abruptly within a distance of three to seven consecutive thin sections, indicating they were not continuous throughout the axial length of the capillaries. The wide regions of the clefts usually showed linkers, strands of glycocalyx-like material spanning the gap. Linkers may contribute to cell adhesion and possibly form part of a filter within the tortuous paracellular pathway provided by the discontinuous network of tight junctional strands. Human term placental capillaries appear to resemble closely other continuous non-brain capillaries.

Capillaries↗
PubMed1992

The interendothelial junction in myocardial capillaries: evidence for the existence of regularly spaced, cleft-spanning structures.

Water and hydrophilic solutes cross the endothelium of continuous capillaries via the paracellular cleft and possibly other routes. This pathway shows a selectivity to molecule size and charge. However, it is not yet known which systems confer this selectivity. Isolated rat hearts were perfusion-fixed through the coronary circulation, stained with lanthanum or tannic acid, and further processed for transmission electron microscopy. Thin sections viewed at x 160,000 magnification revealed regularly spaced, cleft-spanning structures in the wider zone of a small percentage of clefts in addition to at least one zonula occludens. Goniometric tilting of the specimen in steps of 5 degrees perpendicular to the plane of the wide zone showed that such "linkers" can be revealed in at least 40% of all clefts. They become visible at some tilt angles, although the same area of the cleft is featureless at other angles. Single linker spacing measurements were obtained using a computerized image analysis system, and compiled in a frequency distribution chart. On the basis of these data, two models of a regular linker distribution within the cleft are illustrated. Our results provide evidence for the presence of regularly spaced, cleft-spanning structures within the interendothelial cleft which may have implications for endothelial cell-cell adhesion and permeability.

Animals↗
PubMed1991

Immunocytochemical and labelled tracer approaches to uptake and intracellular routing of immunoglobulin-G (IgG) in the human placenta.

Isolated lobules of freshly delivered human term placenta were (a) subjected to an indirect immunoelectron ultracryo method in which the immunoreactivity of endogenous Immunoglobulin-G (IgG) to rabbit anti-human IgG antibody was localized with protein-A-colloidal gold and (b) extracorporeally perfused and human IgG molecules complexed to horseradish peroxidase (HRP) added to the maternal perfusate and the uptake of IgG-HRP over different perfusion durations visualized ultrastructurally by using diaminobenzidine cytochemistry. Immunoreactivity to anti-human IgG antibody was localized all along the apical plasmalemma, in apical coated and uncoated vesicles, in apical and juxtanuclear multivesicular bodies, and in basal vesicles of the syncytiotrophoblast layer of the placenta. The stroma separating the syncytiotrophoblast from the foetal endothelium as well as vesicles within the endothelium were immunoreactive. No immunoreactivity was localized in paracellular clefts of endothelia. A similar distribution of exogenous IgG-HRP was observed for the perfused placentae. When bovine IgG-HRP or HRP alone were used as control tracers no uptake was seen for the former whilst the latter was observed only in early endosomal vesicles of the syncytiotrophoblast. The pattern of localization visualized in both studies is consistent with receptor-mediated uptake of IgG by the syncytiotrophoblast and a vesicular transport of IgG across the foetal endothelium.

Female↗
PubMed1990

Uptake and intracellular routing of peroxidase-conjugated immunoglobulin-G by the perfused human placenta.

Selected lobules of term human placenta were extracorporeally perfused and human immunoglobulin-G complexed to horseradish peroxidase (IgG-HRP) was added to the maternal perfusate. After different durations of perfusion IgG-HRP was visualised by use of diamino-benzidine cytochemistry. Within the first 10 min of perfusion IgG-HRP was found bound to microvilli and coated pits of the syncytiotrophoblast; internalisation into coated vesicles and tubulo-vesicular bodies was also observed. Subsequently, IgG-HRP was found in multivesicular bodies and by 30 min appeared in basal vesicles, the frequency of the latter event increasing with time. No routing of IgG-HRP into Golgi regions or lysosomes could be detected. by 60 min IgG-HRP was found in a few caveolae of fetal endothelium of both terminal and intermediate villi. IgG-HRP was not found in intercellular clefts of the endothelium. The pattern of uptake and routing observed suggests a receptor-mediated transcytosis of IgG-HRP across the syncytiotrophoblast and a transcellular pathway through the endothelium.

Animals↗
PubMed1989

Immunogold localisation of endogenous immunoglobulin-G in ultrathin frozen sections of the human placenta.

Endogenous immunoglobulin-G was localised in ultrathin frozen sections of human term placenta by use of an indirect immuno electron-histochemical methodology. Immunoreactivity of endogenous IgG to rabbit anti-human immunoglobulin-G antibody was visualised by use of protein-A--colloidal gold complex. Gold marked the syncytiotrophoblast in both coated and uncoated regions of the apical plasmalemma, in vesicles and multivesicular bodies, and in vesicles near the basal plasmalemma. Immunoreactivity was also seen in the interstitial space between the trophoblast and the fetal endothelial layer as well as in various types of vesicles within the endothelial cells. No immunoreactivity was seen in the intercellular clefts of the endothelium. The pattern of localisation observed is consistent with receptor-mediated uptake of immunoglobulin-G into the syncytiotrophoblast of the human placenta followed by release into the interstitial space and then vesicular transport through the endothelium.

Female↗
PubMed1989

Effect of hypoxia on endothelial morphology and interendothelial junctions in the isolated perfused rat heart.

Isolated perfused rat hearts were used to assess the effect of 30 or 60 mins of hypoxia on the ultrastructure of the capillary endothelium and particularly on the interendothelial junctions. Perfusions were carried out both in the presence and absence of albumin. Albumin had no effect on ultrastructure or membrane spacing in the interendothelial clefts, neither in oxygenated controls nor in hypoxic hearts. After 30 and 60 mins of hypoxia some capillaries showed endothelial swelling while after 60 mins the endothelium of others was attenuated. The wide regions of the intercellular cleft were not affected by hypoxia but the "narrow zone" gap between membranes became significantly smaller. We conclude that factors within the clefts other than the "tightness" of the narrow zones are responsible for changes in permeability in hypoxia and with albumin.

Animals↗
PubMed1988

Effects of starvation, feeding, and time of day on the activity of proton transport adenosine triphosphatase in the parietal cells of the mouse gastric glands.

The effects of starvation, feeding, and time of day on mouse gastric glands were studied by means of an enzyme histochemical method for K+-dependent p-nitrophenyl phosphatase (K+-NPPase), a partial reaction of the proton pump ATPase which drives gastric acid secretion. The stomachs of mice starved for 24 h showed very low levels of parietal cell K+-NPPase histochemical reaction. However, a brief meal following such a period of starvation produced an abrupt increase in K+-NPPase reaction within most of the parietal cell-containing glands though not all parietal cells were equally susceptible to stimulation. The number of glands containing K+-NPPase-reactive parietal cells fell slowly in the hours following a feeding stimulus. These changes were shown to be caused by feeding rather than by general arousal and to follow the feeding cycle in ad libitum fed animals. The reasons that parietal cells in the basal parts of mouse gastric glands cannot be induced to show K+-NPPase reactivity by a feeding stimulus are not understood.

Adenosine Triphosphate↗
PubMed1988

Interendothelial junctions of cardiac capillaries in rats: their structure and permeability properties.

The isolated perfused heart model was used to examine the structure of rat cardiac capillaries and their permeability to macromolecules of various sizes. Haemoglobin (diameter 6.4 nm) and catalase (10.4 nm) did not cross the endothelium but remained on the luminal side. Cytochrome C (3 nm) and horseradish peroxidase (6 nm) both crossed the endothelium to the subendothelial space and filled the caveolae on the abluminal side as well as the entire length of the lateral intercellular spaces. The membranes of the endothelial cells are separated by an intercellular gap of mean width 18.2 nm. At one or more zonular regions within each lateral intercellular space the two membranes approach each other more closely and frequently appear to fuse. However, tilting the specimen shows that, in these regions, there is a gap of mean width 5.4 nm (in lanthanum- and tannic acid-treated tissue, 3.8 nm in ferrocyanide-treated tissue) between the membranes. We conclude that these narrow regions sieve macromolecules on the basis of size although other factors may determine their permeability properties.

Animals↗
PubMed1987

Quantitative assessment of Na+,K+-ATPase localization by direct and indirect p-nitrophenyl phosphatase methods.

Na+,K+-ATPase histochemistry, using direct (Pb) and indirect (Mg/Sr-Co) p-nitrophenyl phosphatase methods, was assessed by scanning integrative microdensitometry of three classes of tubules in mouse and guinea pig kidneys. The methods yielded similar and appropriate patterns of activity distribution and inhibitor response. The indirect method gave preferable results, in that non-enzymic background was lower and rate of reaction product accumulation was considerably higher.

4-Nitrophenylphosphatase↗
PubMed1984

A comparison of the effects of different perfusion regimes on the structure of the isolated human placental lobule.

Isolated lobules of normal term human placentas were perfused using two different procedures. In the first more conventional system, open-circuit perfusion of both the maternal and the fetal circulations with Earle's solution containing dextran was established and maintained for either 30 min or 1 h. In the second series of experiments both circulations were perfused in separate closed circuits with a mixture of fresh autologous fetal blood and Earle's solution for 0, 1, 2 or 3 h. In both series the lobule was then fixed by perfusion through the fetal circulation. Light- and electron-microscopic examination of a set of tissue samples from each perfused lobule showed substantial differences between the effects of these two types of perfusion procedure. Tissue from lobules perfused by the open-circuit blood-free procedure showed patchy but severe cell swelling and vacuolation of the trophoblast after only one hour's perfusion. Particularly striking was swelling and disruption of a large proportion of the mitochondria in all placental cell types. By contrast, placental tissue from the closed-circuit perfusion with blood-containing medium showed little change over a period of two hours, while after three hours it showed oedema and microvillous damage, but no sign of cell swelling and little mitochondrial damage. It is concluded that the viability of the perfused human placental lobule depends on the type of perfusate used, and that the use of a fetal blood-enriched perfusate is of considerable value in maintenance of the preparation as assessed by structural criteria.

Culture Media↗
PubMed1983

Molecular charge as a determinant of macromolecule permeability across the fetal capillary endothelium of the guinea-pig placenta.

The effect of molecular charge on the permeability to macromolecules of the fetal capillary endothelium of the guinea-pig placenta has been investigated. In a series of experiments for horseradish peroxidase (HRP) isoenzymes with different isoelectric points were perfused through the fetal circulations of guinea-pig placentae, which were then prepared for ultracytochemical localization of peroxidase activity. It was found that the two anionic HRP tracers did not penetrate the endothelial cell layer of the fetal capillaries. By contrast, both cationic HRP tracers did penetrate; reaction product was found in the subendothelial space underlying the endothelial cell layer. The route of transendothelial penetration was via the lateral intercellular spaces (LIS) between endothelial cells. In further experiments cationic and anionic ferritins were perfused. Cationic ferritins were found apparently bound in clusters to the luminal surface of the endothelial cell layer in the luminal ends of the LIS whereas very few anionic ferritin molecules were present. We conclude that molecular charge is an important determinant of macromolecule permeability through the fetal capillary endothelium of the guinea-pig placenta and may be related to the presence of anionic sites on the luminal plasma membrane of the endothelial cells.

Animals↗
PubMed1983

Cytochemical evidence for functional zonation of parietal cells within the gastric glands of the mouse.

Parietal cells in the luminal segments of mouse gastric glands show high activity of acid-secreting potassium-dependent adenosine triphosphatase (H+, K+-ATPase) and of nicotinamide adenine dinucleotide-linked isocitrate dehydrogenase (NAD-ICDHase) and malate dehydrogenase (MDHase) but low activity of succinate dehydrogenase (SDHase). This pattern of activity is reversed in the basal segments of the same glands. These results and previous morphological findings support the conclusion that luminal segment parietal cells are much more active in hydrochloric acid secretion than those of the basal segment. The origin of this zonation may be either cellular deterioration with age or some more specific form of regulation of parietal cell metabolism.

Adenosine Triphosphatases↗
PubMed1983

The intercellular junctions of guinea-pig placental capillaries: a possible structural basis for endothelial solute permeability.

The endothelial cell junction in guinea-pig placental capillaries consists of a continuous ribbon desmosome (zonula adherens) within which lies a particulate tight junction consisting of between one and five anastomosing strands. The intercellular space at these tight junctions is narrowed and is subdivided by junctional bars which are probably continuous with the intramembrane particle rows seen in freeze-fracture replicas of the junctions. Perfusion with lanthanum salts shows the gaps between the junctional bars to be lanthanum-filled and the entire junction to be lanthanum permeable. The estimated size of the spaces between the junctional bars is consistent with the junctional pore size indicated by previous ultrastructural tracer studies. The wider lateral intercellular space of the ribbon desmosome is spanned by more widely spaced "linkers" which may act as a coarser three-dimensional filter in series with size-limiting pores between the tight junctional bars.

Animals↗
PubMed1982

Permeability of the foetal capillary endothelium of the guinea-pig placenta to haem proteins of various molecular sizes.

Haem proteins of different molecular sizes were perfused into the foetal circulation of the guinea-pig placenta to study the permeability of the foetal endothelium. The smallest molecules tested, microperoxidase (ae 1.0 nm) and cytochrome C (ae 1.5 nm), readily penetrated the endothelium; tracer-reaction product was found in the subendothelial space of the capillaries. However, there was no uptake of these two tracers into the syncytiotrophoblast layer of the placenta. An intermediate-sized molecule, myoglobin (ae 1.7 nm) produced only a weak reaction product in the subendothelial space even when perfused at high concentration. The largest molecule tested, haemoglobin (ae 2.8 nm), did not penetrate the foetal endothelium at any of the concentrations employed. The foetal capillary endothelium thus provided a barrier to protein penetration from the foetal circulation, dependent on molecular size. There was evidence that the site of this barrier was located in the lateral intercellular spaces between the endothelial cells. The syncytiotrophoblast of this haemomonochorial placenta provided an almost absolute barrier to protein penetration from the foetal circulation. As other workers have described maternal-to-foetal transmission of proteins across this layer in the guinea-pig, a working hypothesis of the role of endothelium and syncytiotrophoblast in maternal/foetal protein exchange is discussed.

Animals↗
PubMed1981

Ultrastructural study of the permeability of the guinea-pig placenta to horseradish peroxidase.

Horseradish peroxidase (HRP) was used to study macromolecule permeation into the guinea-pig placenta perfused in situ. When tissue culture medium 199 (TC 199) was used as fetal-side perfusate, the tracer reaction product was found only lining the fetal endothelium. When a longer period of perfusion with HRP in TC 199 was used, a small amount of reaction product was found in the subendothelial space and syncytiotrophoblastic vesicles, but not in maternal lacunae. In similar experiments using a Krebs bicarbonate Ringer (KRBG) as perfusate the tracer was found (i) lining the fetal endothelium, (ii) in the laternal intercellular spaces of the endothelium, (iii) in the subendothelial space, and (iv) in the maternal lacunae. It is therefore evident that the vehicle influenced the permeability of the guinea-pig placenta to horseradish peroxidase. As other studies have shown that perfusion of the fetal side with salt solution increases pore size, the results with TC 199 are regarded as more representative of the situation in the intact animal. It is therefore suggested that the fetal endothelium of the guinea-pig placenta may be largely impermeable to molecules of the size of horseradish peroxidase (4 nm) or larger.

Animals↗