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G Clough

Publications and source records attributed to G Clough.

At least 19 recordsLinked to original sources
PubMed1999

Experimental models of skin inflammation.

The skin is the most accessible organ of the body in which to view the inflammatory process and its pharmacological modulation. However, there are relatively few studies in which the response of the dermal vasculature to inflammatory stimuli has been assessed quantitatively or the chemical mediators of the response measured directly. The mechanisms underlying these responses remain unclear despite the fact that altered microvascular function plays an important part in a number of clinical conditions. This paper describes recent studies in which an experimental model of inflammation in the skin has been used to investigate the pharmacological mechanisms underlying microvascular responses. As allergen-induced cutaneous weal and flare responses are mediated mainly by histamine, we first set out to characterize the vascular responses using the intradermal injection of histamine as a first step, experimental model of allergic skin disease. To quantify the inflammatory responses and to explore the mediator mechanisms underlying them we have combined the techniques of scanning laser Doppler imaging of blood flux and dermal microdialysis to make simultaneous measurements of changes in skin blood flow and the release of mediators within the weal and flare response to intradermal injection of histamine in human skin, in vivo.

Animals↗
PubMed1995

A positive, individually ventilated caging system: a local barrier system to protect both animals and personnel.

Most local barrier systems are designed primarily either to protect animals from airborne contamination (exclusion) or to ensure the safety of personnel (hazard containment). Few, other than isolators, are able to cope with the often conflicting demands to do both. The Positive Individually Ventilated system (PIV), which provides pressure adjustable, individual supply and exhaust ventilation to each cage has been tested with this in mind as well as the need to ensure that environmental conditions comply with the requirements of the Home Office Code of Practice (CoP). The results indicate that when compared with traditional open racking the system can reduce both the risk of animals becoming contaminated by airborne infection from the room and the risk of aeroallergens escaping from the cages into the room air. At the same time, environmental conditions within the cages are both less variable and less stressful to the occupants. Conditions of air temperature, relative humidity, ventilation rates, light intensity and (with appropriate air handling) sound levels, all comply with or are better than those required by the CoP. Even with the room air change rate set at only 8/h (8 ac/h) the air distribution system results in draught-free cage ventilation rates of around 50-120 ac/h. This means that with at least the PIV exhaust(s) linked directly into the air conditioning system of the building, the size of the latter and its associated running costs can be reduced by around 50%; this energy saving concept has been approved in principle by the Home Office. Additional benefits include the fact that bedding is kept much drier allowing further cost savings in bedding and associated labour costs. The system is thus beneficial to the animals in protecting them from airborne infection and other stresses. By providing a less variable environment it also helps to minimise the sort of interference with experiments which can arise from that source. Similarly, in accordance with the aims of 'The Control of Substances Hazardous to Health Regulations' (COSHH 1988) and the Health & Safety Executive (HSE 1990), by reducing dust levels in the room air, including allergens, it is also beneficial to the personnel working in the animal rooms.

Air Pollutants, Occupational↗
PubMed1992

Plasma proteins modify the endothelial cell glycocalyx of frog mesenteric microvessels.

1. We have investigated the interaction of plasma proteins with the endothelial cell using cationized ferritin as a marker of the cell surface glycocalyx. 2. Single microvessels of the frog mesentery were sequentially perfused using glass micropipettes with solutions containing cationized ferritin (CF, 6.7 mg ml-1) in 0.10 M-NaCl and then with either frog plasma or bovine serum albumin (BSA; 50 or 10 mg ml-1), or protein-free Ringer solution, before suffusion fixation in 2.5% glutaraldehyde. 3. A layer of CF, usually two to four molecules thick, was associated with the luminal endothelial cell surface. In vessels post-flushed with protein-free Ringer solution the CF layer was closely adherent to all regions of the luminal endothelium, including the plasma membrane, vesicle diaphragms, coated pits and the entrances to clefts. However, when plasma was present during fixation the CF layer was separated from the cell surface by up to 100 nm over all regions. In vessels post-flushed with BSA the CF layer was also separated from the membrane but the effect was less striking. 4. The association of cationized ferritin with the endothelial cell surface was assessed quantitatively using electron micrographs of transverse sections (approximately 50 nm thick) of the perfused vessels, and expressed in terms of the depth of the layer of CF associated with the endothelial cell surface, its separation from the plasma membrane of the luminal endothelium, and the concentration of CF in the layer. The mean (+/- S.D.) separation in the presence of plasma, 32.3 +/- 10.5 nm (n = 12), was significantly greater (P less than 0.01) than that with either protein-free Ringer solution, 3.0 +/- 1.4 nm (n = 9), or BSA in Ringer solution, 8.3 +/- 3.0 nm (n = 8). The separation seen with BSA in Ringer was also significantly greater than that measured with a final Ringer solution perfusion (P less than 0.01). The effects of 10 and 50 mg ml-1 BSA were not different from one another. The total glycocalyx thickness, defined as the sum of the separation layer and depth of CF layer, with plasma present, 56.2 +/- 13.7 nm, was twice the value seen with Ringer solution, 28.0 +/- 9.1 nm (P less than 0.01), while the total thickness with BSA, 30.9 +/- 5.4 nm, was not different from the Ringer solution value.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Immunoperoxidase labelling of albumin at the endothelial cell surface of frog mesenteric microvessels.

Albumin was visualised at the endothelial cell surface of perfused frog mesenteric microvessels using immuno-peroxidase labelling. Vessels in the mesenteries of pithed frogs were washed free of blood and then perfused with frog Ringer solutions containing bovine serum albumin (BSA) at a concentration of 20 mg BSA ml-1, followed by a brief Ringer flush to remove excess albumin from the vessel lumen. The tissues were fixed in 1% glutaraldehyde and a double antibody labelling technique used to identify albumin within the tissue. A dense layer of peroxidase reaction product was seen, which extended 25-50 nm into the vessel lumen. It appeared as a continuous layer lining the luminal openings of interendothelial cell clefts and vesicles open to the luminal cell surface. In some vessels a more irregular layer of peroxidase labelled albumin was seen extending 150 to 200 nm into the vessel lumen, whilst in others clumps of peroxidase labelled albumin were also seen within the vessel lumen. These data offer direct evidence that BSA does interact with the endothelial cell surface of perfused frog mesenteric microvessels but suggest that a proportion is loosley or non-specifically bound to the cell surface and can be removed by a brief Ringer flush. The remainder appears more tightly bound and resistant to Ringer flush.

Animals↗
PubMed1991

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)

Animals↗
PubMed1991

Enhanced fluid uptake in frog mesenteric capillaries associated with plasmin perfusion.

1. We have measured the permeability of single capillaries of the mesenteries of decerebrated frogs, before and during perfusion with solutions containing the fibrinolytic enzyme, plasmin. 2. The hydraulic permeability (Lp) and the effective oncotic pressure exerted across the vessel walls (sigma delta pi) were measured using the method of Michel (1980). The vessels were sequentially perfused with a control frog Ringer solution containing either Ficoll 70 or bovine serum albumin (BSA) at concentrations of 40 mg ml-1 or a mixture of Ficoll 70 (40 mg ml-1) and BSA (10 mg ml-1), and then with a second Ringer perfusate containing plasmin (1 mg ml-1) but in all other respects identical to the control solution. 3. In sixteen out of seventeen experiments, perfusion with plasmin increased sigma delta pi. In eleven of these experiments the increase was very large such that sigma delta pi exceeded the in vitro value for perfusate oncotic pressure. 4. In the same seventeen vessels plasmin perfusion was associated with a fall in Lp from a mean value of 10.3 x 10(-7) cm s-1 cmH2O-1 to one of 7.7 x 10(-7) cm s-1 cmH2O-1. The fall in Lp was not significant. 5. In five of the seventeen vessels, a second control perfusion was made after exposure to plasmin. There was no evidence that Lp had increased above or sigma delta pi had fallen below the initial control value. 6. In a further six experiments, the effects of plasmin were investigated in the absence of other perfusate macromolecules. No significant changes in Lp or sigma delta pi were observed. 7. In a further eight vessels, the effects of plasmin on fluid filtration were investigated with the tissues cold and then at room temperature. In all eight vessels plasmin reduced filtration or increased fluid reabsorption to a greater extent when the tissue temperature was 17 degrees C than when it was 4 degrees C. 8. The large increases in sigma delta pi which we have observed during perfusion of single vessels with plasmin-containing solutions are consistent with the development of substantial local osmotic gradients at the capillary wall following the enzyme's action upon substrates at the endothelial cell surface, one of which could be fibrin. Alternatively, plasmin might stimulate endothelial cells to liberate molecules which locally amplify the oncotic pressure exerted by the perfusate macromolecules. These effects are more marked at room temperature than at 4 degrees C.

Animals↗
PubMed1989

Effects of hydroxyethyl rutosides upon the permeability of single capillaries in the frog mesentery.

1. We have investigated the effects of a standardised mixture of hydroxyethyl rutosides (HR) upon the permeability of the walls of single capillaries and venules of the frog mesentery. 2. In each experiment a single vessel was perfused via a micropipette with frog Ringer solutions containing bovine serum albumin (10 mg ml-1) and Ficoll 70 (40 mg ml-1) first in the absence of HR and then with HR added to the perfusate. The permeability of the vessel walls was assessed during each perfusion by using a development of the Landis micro-occlusion technique to estimate their hydraulic permeability (Lp) and the effective osmotic pressure (sigma delta pi) exerted across them by the perfusate macromolecules. 3. Measurements were made both in vessels which appeared to be healthy and in vessels showing signs of stasis or inflammation before perfusion. 4. HR at concentrations of 1.0, 0.1 and 0.01 mg ml-1 reduced hydraulic permeability to approximately half of its value in the absence of HR. It increased sigma delta pi to macromolecules at concentrations of 10, 1.0, 0.1, 0.01 and 0.001 mg ml-1. The effects of HR upon permeability were not reversed within 10 min of perfusion with an HR-free solution. 5. Ultrastructural examination of a number of vessels in which initial high values of permeability were reduced to values within the normal range of permeabilities by HR, showed clear signs of damage to the endothelium, with large gaps between adjacent endothelial cells. 6. These observations suggest that HR does reduce microvascular permeability both in healthy vessels and vessels showing of inflammation. The reduction in permeability of inflamed vessels does not appear to be the result of closure of the gaps between adjacent endothelial cells.

Animals↗
PubMed1988

The ultrastructure of frog microvessels following perfusion with the ionophore A23187.

The ultrastructure of frog mesenteric capillaries and venules has been examined after the permeability of these vessels to fluid and macromolecules has been increased to a measured extent by perfusion with the ionophore A23187. An average 4.5-fold increase in hydraulic permeability in thirteen vessels was associated with the presence of gaps between the endothelial cells and marked attenuation of endothelial cytoplasm with the appearance of many fenestrations. The changes in ultrastructure suggested much larger increments in permeability than had been measured in these same vessels in vivo.

Animals↗
PubMed1988

Inflammatory changes in permeability and ultrastructure of single vessels in the frog mesenteric microcirculation.

1. In fifteen experiments, single microvessels in the exposed mesenteries of pithed frogs were perfused with Ringer solutions containing bovine serum albumin (40 mg ml-1). For each vessel, the hydraulic permeability of its walls (Lp) and effective osmotic pressure exerted across them (sigma delta pi) were determined from measurements of fluid filtration rates at two capillary pressures (Michel, Mason, Curry, Tooke & Hunter, 1974) before and at predetermined times after the tissue temperature had been raised abruptly from approximately 15 degrees C to 30-35 degrees C. Temperatures greater than 30 degrees C appear to damage the tissues of frogs acclimatized to temperatures of 5-10 degrees C. 2. In fourteen out of fifteen experiments Lp rose when the temperature was raised to 30-35 degrees C. In twelve of these experiments the increase in Lp was greater than expected from the fall in water viscosity with temperature, and was progressive. In five vessels where measurements were made 1-2 min after tissue temperature was raised, Lp increased from an initial mean value (+/- S.E.M.) of 3.76 (+/- 0.54) x 10(-3) micron s-1 cmH2O-1 to one of 8.72 (+/- 1.68) x 10(-3) micron s-1 cmH2O-1. In nine vessels where measurements were made at 10 min after tissue temperature was raised, Lp increased from an initial mean value of 4.03 (+/- 0.72) x 10(-3) micron s-1 cmH2O-1 to one of 16.9 (+/- 3.5) x 10(-3) micron s-1 cmH2O-1. Further increases in Lp were seen at 15 and 20 min. 3. The changes in the effective osmotic pressure opposing filtration, sigma delta pi, were very variable. Out of the twelve vessels which showed large changes in Lp with tissue heating, four showed no reduction in sigma delta pi after 10 min, though sigma delta pi fell in three of these vessels at 15 min. In the other eight vessels, sigma delta pi fell as Lp rose. A quantitative theory developed in this paper allowed the changes in sigma delta pi to be analysed in terms of a component across the regions of vessel wall of increased permeability (sigma H delta pi H) and a component across regions where Lp was unchanged. In six vessels sigma H delta pi H approximated to zero; in two vessels sigma H delta pi H was 6.2 and 4.5 cmH2O.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Quantitative comparisons of hydraulic permeability and endothelial intercellular cleft dimensions in single frog capillaries.

1. We have investigated the ultrastructure of the intercellular clefts of the walls of single capillaries and venules of the frog mesentery in which the hydraulic permeability (Lp) and the reflection coefficient of the vessel walls to serum albumin (sigma BSA) had been measured using the micro-occlusion technique of Michel (1980). Our aim was to investigate whether the dimensions of the clefts were sufficient to accommodate the pathways through the vessel walls necessary to account for the measured permeability. 2. Lp was measured in seventeen individually perfused vessels. The walls of fourteen of these were relatively impermeable to macromolecules with a sigma to albumin greater than 0.66 (mean value 0.83, S.E.M. +/- 0.04). The Lp of these fourteen vessels ranged from 1.8 x 10(-7) to 12.5 x 10(-7) cm s-1 cmH2O-1 and had a mean value of 5.9 (S.E.M. +/- 0.85) x 10(-7) cm s-1 cmH2O-1. 3. Cleft dimensions estimated from electron micrographs of 642 transversely sectioned endothelial cell junctions from the same seventeen vessels gave a value for the mean cleft width (W) of 0.0220 micron (S.E.M. +/- 0.0064 micron). The mean depth of the clefts from luminal to abluminal surface of the endothelium (delta x) was 0.395 micron (S.E.M. +/- 0.091 micron) with a range of 0.104-1.70 micron. The cleft length per unit area of cell wall (L), calculated using the formulation of Bundgaard & Frøkjaer-Jensen (1982), was 2064 (S.E.M. +/- 112) cm cm-2. Measurements were also made of cleft dimensions from longitudinally sectioned junctions from five of the seventeen vessels. 4. The fraction of the surface area of capillary wall occupied by the clefts (Ap = LW) had a mean value of 0.0048 (+/- 0.00014) for all seventeen vessels with a range of 0.0030-0.0074 when estimated from transverse sections. There was no correlation between the variation of Lp between different vessels and the variations of Ap. 5. Data from the fourteen vessels when sigma BSA was greater than 0.66 revealed a correlation between values of Lp and the reciprocal of delta x (r = 0.6675, P less than 0.01). No correlation was found between Lp and the mean thickness of the endothelial cells in the vicinity of the clefts. This is strong evidence for the intercellular cleft being the principal pathway for fluid movements. Variation in cleft depth appears to be a factor determining variation in permeability between different capillaries.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

The effects of chemical fixation on the permeability of frog mesenteric capillaries.

1. We have investigated the effects on microvascular permeability of two chemical fixatives, glutaraldehyde/formaldehyde mixture and osmium tetroxide, both of which are used widely in electron microscopy. 2. The permeability of single perfused frog mesenteric capillaries was assessed using the technique of Michel (1980) to estimate the hydraulic conductance (Lp) of the vessel walls and the effective osmotic pressure (sigma delta pi) which could be exerted across them by the neutral macromolecule, Ficoll 70. 3. In each experiment, Lp and sigma delta pi were estimated in the same capillary before and after chemical fixation with either an aldehyde mixture (n = 6) or 1% osmium tetroxide (n = 6). In the absence of serum proteins in the perfusate, the values of Lp recorded prior to fixation were high. The effect of both fixatives was to reduce Lp. With aldehydes the mean value (+/- S.E.M.) of Lp fell from 22.1 (+/- 6.3) x 10(-3) to 5.7 (+/- 2.0) x 10(-3) microns s-1 cmH2O-1. With osmium tetroxide the mean Lp fell from 29.1 (+/- 8.5) x 10(-3) to 8.6 (+/- 3.6) x 10(-3) microns s-1 cmH2O-1. 4. The perfusates contained the neutral macromolecule, Ficoll 70, at a concentration of 60 mg ml-1 which exerted an osmotic pressure of 35 cmH2O in a membrane osmometer. In the absence of plasma proteins in the perfusate, sigma delta pi was only a fraction of this perfusate oncotic pressure prior to fixation. After aldehyde treatment there was a small but insignificant decrease in sigma delta pi. Osmium tetroxide, however, increased sigma delta pi from a mean (+/- S.E.M.) of 6.3 (+/- 1.6) cmH2O before fixation to 16.4 (+/- 2.8) cmH2O after fixation, P less than 0.01 using a paired t test. 5. In three experiments, the reflection coefficient of the capillary wall to NaCl sigma NaCl, was measured using the technique of Curry, Mason & Michel (1976) before and after osmium fixation. Fixation raised sigma NaCl from a mean value (+/- S.E.M.) of 0.009 (+/- 0.001) to one of 0.017 (+/- 0.004). Although these changes may be interpreted as an increase in the contribution to the total Lp of the capillary wall of channels which are available only to water, the changes are too small for such a mechanism to account for the increase in reflection coefficient to Ficoll 70. 6. The reduction in Lp following chemical fixation could represent an increase in the hydraulic resistance of either the capillary wall itself, or in the tissues surrounding the vessel.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

A quantitative study of the exchange microvasculature of muscles from the human foot and hand.

In this study, transmission electron microscopy has been used to make a quantitative assessment of the exchange surface area of the microvessels of skeletal muscle from the human foot and hand. The numbers of capillaries per unit area of skeletal muscle were found to be similar in the foot (47.9 X 10(3) SEM +/- 7.5 X 10(3) cm-2) and the hand (49.3 X 10(3) SEM +/- 9.0 X 10(3) cm-2). However, the capillaries of the foot appeared significantly larger than those of the hand, having a mean diameter of 5.4 +/- 0.1 microns compared with 4.4 +/- 0.2 microns in the hand. Measurement of total capillary exchange surface area (SA) from low power (X 3000) electron micrographs of muscle samples from 11 subjects gave values of SA of 93.9 +/- 5.9 cm2/g tissue (n = 5) in the foot and 83.8 +/- 5.4 cm2/g tissue in the hand (n = 6). High power electron micrographs (X 21,600) of individual vessels showed the walls of the capillaries of the feet to be significantly thicker than those of the hand. The increase in wall thickness was mainly due to a 40% increase in the width of the basement membrane, which had a mean width of 221 +/- 16 nm in the hand and 312 +/- 34 nm in the foot.

Capillaries↗
PubMed1984

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.

Animals↗
PubMed1983

The effects of cationised ferritin and native ferritin upon the filtration coefficient of single frog capillaries. Evidence that proteins in the endothelial cell coat influence permeability.

To investigate whether certain macromolecules reduce capillary permeability by binding to the surface coat of endothelial cells, the effects of cationised ferritin (CF) upon the filtration coefficient (Lp) of individually perfused frog mesenteric capillaries were compared with those of native ferritin (NF). With perfusate CF concentrations between 0.1 g 100 ml-1 and 2.5 g 100 ml-1, Lp was reduced to approximately 30% of its value for the same vessel perfused with protein-free Ringer solution. Electron micrographs of the perfused capillaries revealed that over this range of perfusate concentrations. CF was concentrated uniformly in the endothelial cell coat, occupying 8.5% of its volume. Neither the effect of cationised ferritin upon Lp nor its concentration in the cell coat varied significantly over this range of perfusate concentrations. When perfusate concentration of CF was reduced to 0.01 g 100 ml-1, CF no longer reduced Lp and its concentration in the cell coat fell below 2%. Native ferritin, which is excluded from the cell coat, did not reduce Lp at a perfusate concentration of 0.1 g 100 ml-1. At a concentration of 2.5 g 100 ml-1, NF reduced Lp in a few very permeable vessels (Lp greater than 60 X 10(-3) microns sec-1 cm H2O-1) but had no significant effect on vessels with lower and more normal values of Lp. The effects of CF upon Lp can be described in terms of the Kozeny equation if a major proportion of the hydraulic resistance through the capillary wall is attributed to a fiber protein matrix.

Animals↗
PubMed1982

The slit catheter: a comparison with the wick catheter in the measurement of compartment pressure.

The slit catheter, a new instrument for the measurement of compartment pressure, has been compared with the wick catheter in experimental conditions. The two catheters were inserted into the anterior tibial compartments of 8 human legs and controlled external pressures were applied by means of an inflatable limb bag. The mean resting intramuscular pressure of 8.5 +/- 6.2 mmHg for the slit and 8.7 mmHg +/- 6.2 mmHg for the wick catheter agrees with that of other workers, and the slit catheter records a pressure at all applied external pressures not significantly different from the wick catheter (paired t test). The slit catheter provides a simple and inexpensive way of estimating compartment pressure which is as accurate as a method widely used both experimentally and clinically in North America.

Catheterization↗
PubMed1982

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.

Animals↗