Charles Michel - Academia.edu (original) (raw)
Papers by Charles Michel
The Journal of physiology, 1978
International journal of microcirculation, clinical and experimental / sponsored by the European Society for Microcirculation, 1987
Respiration Physiology, 1968
Abstract The buffering of the blood during hypoxaemia and during respiratory exchange in the lung... more Abstract The buffering of the blood during hypoxaemia and during respiratory exchange in the lungs and in the tissues is considered in the presence of factors known to influence the in vivo buffering of CO2 alone. It is argued that during systemic hypoxaemia or asphyxia the Haldane effect in the circulating blood has a smaller value than it has in vitro, but during respiratory exchange in the lungs and in the tissues, the Haldane effect retains its full in vitro value. Changes in arteriovenous differences can be shown to appear to alter the acid-base characteristics of the arterial blood. It is concluded that the in vivo CO2 dissociation curve is the dissociation curve of mixed venous blood and that the arterial blood is related to the mixed venous blood through the in vitro dissociation curve.
The Journal of Physiology, 1996
1. We have investigated the effects of microvascular pressures, high enough to rupture the vessel... more 1. We have investigated the effects of microvascular pressures, high enough to rupture the vessel wall, upon the ultrastructure and permeability of mesenteric capillaries in pithed frogs. 2. The vessels were perfused via micropipettes with Ringer solutions containing bovine serum albumin (1 mg ml-') and a few human red cells. After a perfused section of vessel had been closed downstream, pressure (applied via the micropipette) was raised in a series of steps of 10 mmHg, each lasting approximately 10 s, until the vessel ruptured. Fluid filtration through the vessel wall prior to rupture was estimated from the movements of the red cells. 3. Seven vessels were fixed in glutaraldehyde immediately after rupture and prepared for electron microscopy. The electron micrographs revealed openings in the vessel walls and thirty-six of these gaps were completely defined in runs of serial sections made on four of the vessels. Twenty-nine of these gaps passed through the endothelial cells (transcellular) and seven were intercellular. 4. The pressure at which a vessel ruptured, Pb, was measured in twenty-nine vessels and had a mean + S.E.M. value of 79-6 + 5.0 cmH2O. In ten of these vessels, which had a mean + S.E.M. Pb of 84-2 + 6-5 cmH2 0 microvascular pressure was lowered immediately after the initial rupture and the vessel perfused at a pressure of 20 cmH2O. Pb was then remeasured and found to be 69-9 + 8-4 cmH20, which was not significantly different from its initial value. 5. Hydraulic permeability (Lp) was measured in six vessels over the range of 15-30 cmH20 before and 10 min after the vessel wall ruptured at high pressure. Mean values were 5.5 x 10-7 and 4 0 x 10-7 cm s-cmH20-1 and were not significantly different. 6. At pressures equal to and 10 mmHg below Pb, small short-lived increases in filtration rate were observed. It is suggested that these may correspond to the increased permeability to fluid and macromolecules observed at high microvascular pressures in intact capillary beds.
Microcirculation, 2012
Visualising the molecular strands making up the glycocalyx in the lumen of small blood vessels ha... more Visualising the molecular strands making up the glycocalyx in the lumen of small blood vessels has proved to be difficult using conventional transmission electron microscopy techniques. Images obtained from tissue stained in a variety of ways have revealed a regularity in the organisation of the proteoglycan components of the glycocalyx layer (fundamental spacing about 20 nm), but require a large sample number. Attempts to visualise the glycocalyx face-on (i.e. in a direction perpendicular to the endothelial cell layer in the lumen and directly applicable for permeability modelling) has had limited success (e.g. freeze fracture). A new approach is therefore needed. Here we demonstrate the effectiveness of using the relatively novel electron microscopy technique of 3D electron tomography on two differently stained preparations to reveal details of the architecture of the glycocalyx just above the endothelial cell layer. One preparation uses the novel staining technique using Lanthanum Dysprosium Glycosamino Glycan adhesion (the LaDy GAGa method).
Biophysical Journal, 2011
The glycocalyx or endocapillary layer on the luminal surface of microvessels has a major role in ... more The glycocalyx or endocapillary layer on the luminal surface of microvessels has a major role in the exclusion of macromolecules from the underlying endothelial cells. Current structural evidence in the capillaries of frog mesentery indicates a regularity in the structure of the glycocalyx, with a center-to-center fiber spacing of 20 nm and a fiber width of 12 nm, which might explain the observed macromolecular filtering properties. In this study, we used electron micrographs of tissues prepared using perfusion fixation and tannic acid treatment. The digitized images were analyzed using autocorrelation to find common spacings and to establish whether similar structures, hence mechanisms, are present in the microvessel glycocalyces of a variety of mammalian tissues. Continuous glycocalyx layers in mammalian microvessels of choroid, renal tubules, glomerulus, and psoas muscle all showed similar lateral spacings at~19.5 nm (possibly in a quasitetragonal lattice) and longer spacings above 100 nm. Individual glycocalyx tufts above fenestrations in the first three of these tissues and also in stomach fundus and jejunum showed evidence for similar short-range structural regularity, but with more disorder. The fiber diameter was estimated as 18.8 (5 0.2) nm, but we believe this is an overestimate because of the staining method used. The implications of these findings are discussed.
BMC Nephrology, 2014
Background: The human glomerulus is the primary filtration unit of the kidney, and contains the G... more Background: The human glomerulus is the primary filtration unit of the kidney, and contains the Glomerular Filtration Barrier (GFB). The GFB had been thought to comprise 3 layersthe endothelium, the basement membrane and the podocyte foot processes. However, recent studies have suggested that at least two additional layers contribute to the function of the GFB, the endothelial glycocalyx on the vascular side, and the sub-podocyte space on the urinary side. To investigate the structure of these additional layers is difficult as it requires three-dimensional reconstruction of delicate sub-microscopic (<1 μm) cellular and extracellular elements. Methods: Here we have combined three different advanced electron microscopic techniques that cover multiple orders of magnitude of volume sampled, with a novel staining methodology (Lanthanum Dysprosium Glycosaminoglycan adhesion, or LaDy GAGa), to determine the structural basis of these two additional layers. Serial Block Face Scanning Electron Microscopy (SBF-SEM) was used to generate a 3-D image stack with a volume of a 5.3 x 10 5 μm 3 volume of a whole kidney glomerulus (13% of glomerular volume). Secondly, Focused Ion Beam milling Scanning Electron Microscopy (FIB-SEM) was used to image a filtration region (48 μm 3 volume). Lastly Transmission Electron Tomography (Tom-TEM) was performed on a 0.3 μm 3 volume to identify the fine structure of the glycocalyx. Results: Tom-TEM clearly showed 20 nm fibre spacing in the glycocalyx, within a limited field of view. FIB-SEM demonstrated, in a far greater field of view, how the glycocalyx structure related to fenestrations and the filtration slits, though without the resolution of TomTEM. SBF-SEM was able to determine the extent of the sub-podocyte space and glycocalyx coverage, without additional heavy metal staining. Neither SBF-nor FIB-SEM suffered the anisotropic shrinkage under the electron beam that is seen with Tom-TEM. Conclusions: These images demonstrate that the three dimensional structure of the GFB can be imaged, and investigated from the whole glomerulus to the fine structure of the glycocalyx using three dimensional electron microscopy techniques. This should allow the identification of structural features regulating physiology, and their disruption in pathological states, aiding the understanding of kidney disease.
Acta Anaesthesiologica Scandinavica
When Woodcock and Woodcock 1 suggested that more recent work on the physiology of blood-tissue fl... more When Woodcock and Woodcock 1 suggested that more recent work on the physiology of blood-tissue fluid exchange might be relevant in the management of intravenous fluids in clinical situations, they referred to the newer work as the "Revised Starling Principle." Here they were merely adopting the phrase used by Levick & Michel, 2 originated by others 3 to describe these ideas. The name "Revised Starling Principle" or RSP might imply that the original version of the Starling Principle was wrong and required revision. It should be emphasized that Starling's fundamental idea, that movements of fluid between the circulating plasma and the tissues are determined by the differences between hydrostatic pressures and colloid osmotic (or oncotic) pressures across microvascular walls, remains the central idea of the RSP. This essential point seems to have been overlooked by some who may have been confused by the word "Revised" in the title. 4,5 To emphasize that the RSP builds on and extends Starling's original proposal, 6 we first summarize its key elements, which describe how the oncotic pressures of the plasma proteins oppose hydrostatic pressure driven filtration of fluid from blood to tissues, when microvascular walls have low but finite permeabilities to plasma protein. We then briefly review the train of logic on which these developments of Starling's classical principle are based.
Seldin and Giebisch's The Kidney, 2008
Exchange through microvascular walls is both the initial and the final step of transport of mater... more Exchange through microvascular walls is both the initial and the final step of transport of materials by the circulation. In most tissues, microvascular exchange is a passive process, driven by differences in hydrostatic pressure and solute concentration between the circulating plasma and the interstitial fluid that flank microvessel walls. Lipophilic molecules and small water-soluble molecules and ions can exchange rapidly in most vascular beds, but microvascular walls are a barrier to macromolecules, severely impeding their exchange. The consequent differences in macromolecular concentration across microvascular walls are responsible for differences in osmotic pressure, which were identified over a century ago to play an essential role in the balance of fluid between the circulating blood and the tissues.
Exchange through microvascular walls is both the initial and the final step of transport of mater... more Exchange through microvascular walls is both the initial and the final step of transport of materials by the circulation. In most tissues, microvascular exchange is a passive process, driven by differences in hydrostatic pressure and solute concentration between the circulating plasma and the interstitial fluid that flank microvessel walls. Lipophilic molecules and small water-soluble molecules and ions can exchange rapidly in most vascular beds, but microvascular walls are a barrier to macromolecules, severely impeding their exchange. The consequent differences in macromolecular concentration across microvascular walls are responsible for differences in osmotic pressure, which were identified over a century ago to play an essential role in the balance of fluid between the circulating blood and the tissues.
Pressure Ulcer Research, 2005
Transport of Fluid and Solutes in Tissues Charles Michel Introduction The transport of nutrients ... more Transport of Fluid and Solutes in Tissues Charles Michel Introduction The transport of nutrients and metabolites in tissues involves a series of processes of varying degrees of complexity. Some of these are responsible for the transport of all molecules at a particular stage of the ...
When the best available estimates of the blood flow and the permeability-surface area product of ... more When the best available estimates of the blood flow and the permeability-surface area product of the villus microcirculation are used in an analysis of glucose absorption in humans and rats, the concentrations of glucose predicted to be present at the basement membrane of the epithelium rise to values that exceed 100mM. If an increase in villus blood flow did not occur in proportion to the glucose absorption rate, glucose concentration in the tissue would rise to even higher levels. Our tentative estimates of glucose concentration within the epithelial cells suggest that without increases in blood flow and PS of the villus microcirculation the rising levels of intracellular glucose concentration would limit maximal rates of absorption. It would seem that in addition to events occurring in the epithelial cells, the absorption of glucose involves a co-ordinated microvascular response comparable to that occurring in skeletal muscle during exercise.
Journal of lipid research, 2015
The mechanisms by which LDLs and HDLs cross the vascular endothelium from plasma into interstitia... more The mechanisms by which LDLs and HDLs cross the vascular endothelium from plasma into interstitial fluid are not understood, and have never been studied in humans in vivo. We determined whether the plasma-to-lymph clearance rates of LDL and HDL conform with those predicted by passive ultrafiltration through intercellular pores, or if it is necessary to invoke an active process such as receptor-mediated transcytosis. Plasma and afferent peripheral lymph were collected under steady-state conditions from 30 healthy men, and assayed for seven globular proteins of molecular radii 2.89-8.95 nm, complement C3, and apo AI, apo AII, and apo B. Plasma-to-lymph clearance rates of the seven proteins fitted the relation expected for molecules of their size when transported through two populations of pores of radius 4.95 and 20.1 nm. The same model parameters were then found to accurately predict the clearance rates of both HDL and LDL. The apparent clearance of complement C3, previously shown to...
Microcirculation, 2014
To evaluate the dynamics of skin microvascular blood flow (BF) and tissue oxygenation parameters ... more To evaluate the dynamics of skin microvascular blood flow (BF) and tissue oxygenation parameters (OXY) measured simultaneously at the same site using a combined non-invasive BF+OXY+temperature probe. Skin BF, oxygenated (oxyHb) and deoxygenated (deoxyHb) haemoglobin and mean oxygen saturation (SO2 ) were measured in 50 healthy volunteers at rest and during perturbation of local blood flow by post-occlusive reactive hyperaemia, sympathetic nervous system-mediated vasoconstriction (deep inspiratory breath-hold) and local skin warming. Signals were analysed in time and frequency domains. The relationship between BF and SO2 over the range of flows investigated was described by a non-linear equation with an asymptote for SO2 of 84% at BF &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;50 PU. SO2 was independently associated with BF, skin temperature, BMI and age, which together identified 59% of the variance in SO2 (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.0001). Fourier analysis revealed periodic low frequency fluctuations in both BF and SO2 , attributable to endothelial (~0.01 Hz), neurogenic (~0.04 Hz) and myogenic (~0.1 Hz) flow motion activity. The frequency coherence between the BF and SO2 signals was greatest in the endothelial and neurogenic frequency bands. The simultaneous evaluation of microvascular blood flow and oxygenation kinetics in healthy skin provides a platform from which to investigate microvascular impairment in the skin and more generally the pathogenesis of microvascular disease.
Microcirculation, 2012
In this issue of Microcirculation, Wagner, Modla, Hossler and Czmmek describe the use of electron... more In this issue of Microcirculation, Wagner, Modla, Hossler and Czmmek describe the use of electron tomography to visualize the three-dimensional arrangement of small endothelial vesicles and caveolae of muscle capillaries. Their images show the wellknown clusters of fused vesicles communicating with caveolae at the luminal and abluminal surfaces. The advantages of electron tomography are shown by well resolved images of single cytoplasmic vesicles separate from fused vesicle clusters and also by occasional chains of fused vesicles forming trans-endothelial channels. Twenty five to thirty years ago the existence of both trans-endothelial channels and single unattached vesicles was disputed. Also, since some single vesicles and all of the transendothelial channels are labeled with a lanthanide tracer present in the perfusate at the time of fixation, this evidence once again raises the question of whether vesicles have a role in vascular permeability to macromolecules. This brief review describes the origin of the vesicle controversy, some of the more recent evidence for and against the participation of vesicles in macromolecular transport and considers some criticisms of ultrastructural evidence for vesicular transport that still require answers.
Microcirculation, 1997
The Editor gratefully acknoruledges Projkssor Charles Michel for his preparation of this tribute.
Cardiovascular Research, 2010
Microvascular fluid exchange (flow J(v)) underlies plasma/interstitial fluid (ISF) balance and oe... more Microvascular fluid exchange (flow J(v)) underlies plasma/interstitial fluid (ISF) balance and oedematous swelling. The traditional form of Starling&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s principle has to be modified in light of insights into the role of ISF pressures and the recognition of the glycocalyx as the semipermeable layer of endothelium. Sum-of-forces evidence and direct observations show that microvascular absorption is transient in most tissues; slight filtration prevails in the steady state, even in venules. This is due in part to the inverse relation between filtration rate and ISF plasma protein concentration; ISF colloid osmotic pressure (COP) rises as J(v) falls. In some specialized regions (e.g. kidney, intestinal mucosa), fluid absorption is sustained by local epithelial secretions, which flush interstitial plasma proteins into the lymphatic system. The low rate of filtration and lymph formation in most tissues can be explained by standing plasma protein gradients within the intercellular cleft of continuous capillaries (glycocalyx model) and around fenestrations. Narrow breaks in the junctional strands of the cleft create high local outward fluid velocities, which cause a disequilibrium between the subglycocalyx space COP and ISF COP. Recent experiments confirm that the effect of ISF COP on J(v) is much less than predicted by the conventional Starling principle, in agreement with modern models. Using a two-pore system model, we also explore how relatively small increases in large pore numbers dramatically increase J(v) during acute inflammation.
British Journal of Pharmacology, 1989
1. We have investigated the effects of a standardised mixture of hydroxyethyl rutosides (HR) upon... more 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.
The Journal of physiology, 1978
International journal of microcirculation, clinical and experimental / sponsored by the European Society for Microcirculation, 1987
Respiration Physiology, 1968
Abstract The buffering of the blood during hypoxaemia and during respiratory exchange in the lung... more Abstract The buffering of the blood during hypoxaemia and during respiratory exchange in the lungs and in the tissues is considered in the presence of factors known to influence the in vivo buffering of CO2 alone. It is argued that during systemic hypoxaemia or asphyxia the Haldane effect in the circulating blood has a smaller value than it has in vitro, but during respiratory exchange in the lungs and in the tissues, the Haldane effect retains its full in vitro value. Changes in arteriovenous differences can be shown to appear to alter the acid-base characteristics of the arterial blood. It is concluded that the in vivo CO2 dissociation curve is the dissociation curve of mixed venous blood and that the arterial blood is related to the mixed venous blood through the in vitro dissociation curve.
The Journal of Physiology, 1996
1. We have investigated the effects of microvascular pressures, high enough to rupture the vessel... more 1. We have investigated the effects of microvascular pressures, high enough to rupture the vessel wall, upon the ultrastructure and permeability of mesenteric capillaries in pithed frogs. 2. The vessels were perfused via micropipettes with Ringer solutions containing bovine serum albumin (1 mg ml-') and a few human red cells. After a perfused section of vessel had been closed downstream, pressure (applied via the micropipette) was raised in a series of steps of 10 mmHg, each lasting approximately 10 s, until the vessel ruptured. Fluid filtration through the vessel wall prior to rupture was estimated from the movements of the red cells. 3. Seven vessels were fixed in glutaraldehyde immediately after rupture and prepared for electron microscopy. The electron micrographs revealed openings in the vessel walls and thirty-six of these gaps were completely defined in runs of serial sections made on four of the vessels. Twenty-nine of these gaps passed through the endothelial cells (transcellular) and seven were intercellular. 4. The pressure at which a vessel ruptured, Pb, was measured in twenty-nine vessels and had a mean + S.E.M. value of 79-6 + 5.0 cmH2O. In ten of these vessels, which had a mean + S.E.M. Pb of 84-2 + 6-5 cmH2 0 microvascular pressure was lowered immediately after the initial rupture and the vessel perfused at a pressure of 20 cmH2O. Pb was then remeasured and found to be 69-9 + 8-4 cmH20, which was not significantly different from its initial value. 5. Hydraulic permeability (Lp) was measured in six vessels over the range of 15-30 cmH20 before and 10 min after the vessel wall ruptured at high pressure. Mean values were 5.5 x 10-7 and 4 0 x 10-7 cm s-cmH20-1 and were not significantly different. 6. At pressures equal to and 10 mmHg below Pb, small short-lived increases in filtration rate were observed. It is suggested that these may correspond to the increased permeability to fluid and macromolecules observed at high microvascular pressures in intact capillary beds.
Microcirculation, 2012
Visualising the molecular strands making up the glycocalyx in the lumen of small blood vessels ha... more Visualising the molecular strands making up the glycocalyx in the lumen of small blood vessels has proved to be difficult using conventional transmission electron microscopy techniques. Images obtained from tissue stained in a variety of ways have revealed a regularity in the organisation of the proteoglycan components of the glycocalyx layer (fundamental spacing about 20 nm), but require a large sample number. Attempts to visualise the glycocalyx face-on (i.e. in a direction perpendicular to the endothelial cell layer in the lumen and directly applicable for permeability modelling) has had limited success (e.g. freeze fracture). A new approach is therefore needed. Here we demonstrate the effectiveness of using the relatively novel electron microscopy technique of 3D electron tomography on two differently stained preparations to reveal details of the architecture of the glycocalyx just above the endothelial cell layer. One preparation uses the novel staining technique using Lanthanum Dysprosium Glycosamino Glycan adhesion (the LaDy GAGa method).
Biophysical Journal, 2011
The glycocalyx or endocapillary layer on the luminal surface of microvessels has a major role in ... more The glycocalyx or endocapillary layer on the luminal surface of microvessels has a major role in the exclusion of macromolecules from the underlying endothelial cells. Current structural evidence in the capillaries of frog mesentery indicates a regularity in the structure of the glycocalyx, with a center-to-center fiber spacing of 20 nm and a fiber width of 12 nm, which might explain the observed macromolecular filtering properties. In this study, we used electron micrographs of tissues prepared using perfusion fixation and tannic acid treatment. The digitized images were analyzed using autocorrelation to find common spacings and to establish whether similar structures, hence mechanisms, are present in the microvessel glycocalyces of a variety of mammalian tissues. Continuous glycocalyx layers in mammalian microvessels of choroid, renal tubules, glomerulus, and psoas muscle all showed similar lateral spacings at~19.5 nm (possibly in a quasitetragonal lattice) and longer spacings above 100 nm. Individual glycocalyx tufts above fenestrations in the first three of these tissues and also in stomach fundus and jejunum showed evidence for similar short-range structural regularity, but with more disorder. The fiber diameter was estimated as 18.8 (5 0.2) nm, but we believe this is an overestimate because of the staining method used. The implications of these findings are discussed.
BMC Nephrology, 2014
Background: The human glomerulus is the primary filtration unit of the kidney, and contains the G... more Background: The human glomerulus is the primary filtration unit of the kidney, and contains the Glomerular Filtration Barrier (GFB). The GFB had been thought to comprise 3 layersthe endothelium, the basement membrane and the podocyte foot processes. However, recent studies have suggested that at least two additional layers contribute to the function of the GFB, the endothelial glycocalyx on the vascular side, and the sub-podocyte space on the urinary side. To investigate the structure of these additional layers is difficult as it requires three-dimensional reconstruction of delicate sub-microscopic (<1 μm) cellular and extracellular elements. Methods: Here we have combined three different advanced electron microscopic techniques that cover multiple orders of magnitude of volume sampled, with a novel staining methodology (Lanthanum Dysprosium Glycosaminoglycan adhesion, or LaDy GAGa), to determine the structural basis of these two additional layers. Serial Block Face Scanning Electron Microscopy (SBF-SEM) was used to generate a 3-D image stack with a volume of a 5.3 x 10 5 μm 3 volume of a whole kidney glomerulus (13% of glomerular volume). Secondly, Focused Ion Beam milling Scanning Electron Microscopy (FIB-SEM) was used to image a filtration region (48 μm 3 volume). Lastly Transmission Electron Tomography (Tom-TEM) was performed on a 0.3 μm 3 volume to identify the fine structure of the glycocalyx. Results: Tom-TEM clearly showed 20 nm fibre spacing in the glycocalyx, within a limited field of view. FIB-SEM demonstrated, in a far greater field of view, how the glycocalyx structure related to fenestrations and the filtration slits, though without the resolution of TomTEM. SBF-SEM was able to determine the extent of the sub-podocyte space and glycocalyx coverage, without additional heavy metal staining. Neither SBF-nor FIB-SEM suffered the anisotropic shrinkage under the electron beam that is seen with Tom-TEM. Conclusions: These images demonstrate that the three dimensional structure of the GFB can be imaged, and investigated from the whole glomerulus to the fine structure of the glycocalyx using three dimensional electron microscopy techniques. This should allow the identification of structural features regulating physiology, and their disruption in pathological states, aiding the understanding of kidney disease.
Acta Anaesthesiologica Scandinavica
When Woodcock and Woodcock 1 suggested that more recent work on the physiology of blood-tissue fl... more When Woodcock and Woodcock 1 suggested that more recent work on the physiology of blood-tissue fluid exchange might be relevant in the management of intravenous fluids in clinical situations, they referred to the newer work as the "Revised Starling Principle." Here they were merely adopting the phrase used by Levick & Michel, 2 originated by others 3 to describe these ideas. The name "Revised Starling Principle" or RSP might imply that the original version of the Starling Principle was wrong and required revision. It should be emphasized that Starling's fundamental idea, that movements of fluid between the circulating plasma and the tissues are determined by the differences between hydrostatic pressures and colloid osmotic (or oncotic) pressures across microvascular walls, remains the central idea of the RSP. This essential point seems to have been overlooked by some who may have been confused by the word "Revised" in the title. 4,5 To emphasize that the RSP builds on and extends Starling's original proposal, 6 we first summarize its key elements, which describe how the oncotic pressures of the plasma proteins oppose hydrostatic pressure driven filtration of fluid from blood to tissues, when microvascular walls have low but finite permeabilities to plasma protein. We then briefly review the train of logic on which these developments of Starling's classical principle are based.
Seldin and Giebisch's The Kidney, 2008
Exchange through microvascular walls is both the initial and the final step of transport of mater... more Exchange through microvascular walls is both the initial and the final step of transport of materials by the circulation. In most tissues, microvascular exchange is a passive process, driven by differences in hydrostatic pressure and solute concentration between the circulating plasma and the interstitial fluid that flank microvessel walls. Lipophilic molecules and small water-soluble molecules and ions can exchange rapidly in most vascular beds, but microvascular walls are a barrier to macromolecules, severely impeding their exchange. The consequent differences in macromolecular concentration across microvascular walls are responsible for differences in osmotic pressure, which were identified over a century ago to play an essential role in the balance of fluid between the circulating blood and the tissues.
Exchange through microvascular walls is both the initial and the final step of transport of mater... more Exchange through microvascular walls is both the initial and the final step of transport of materials by the circulation. In most tissues, microvascular exchange is a passive process, driven by differences in hydrostatic pressure and solute concentration between the circulating plasma and the interstitial fluid that flank microvessel walls. Lipophilic molecules and small water-soluble molecules and ions can exchange rapidly in most vascular beds, but microvascular walls are a barrier to macromolecules, severely impeding their exchange. The consequent differences in macromolecular concentration across microvascular walls are responsible for differences in osmotic pressure, which were identified over a century ago to play an essential role in the balance of fluid between the circulating blood and the tissues.
Pressure Ulcer Research, 2005
Transport of Fluid and Solutes in Tissues Charles Michel Introduction The transport of nutrients ... more Transport of Fluid and Solutes in Tissues Charles Michel Introduction The transport of nutrients and metabolites in tissues involves a series of processes of varying degrees of complexity. Some of these are responsible for the transport of all molecules at a particular stage of the ...
When the best available estimates of the blood flow and the permeability-surface area product of ... more When the best available estimates of the blood flow and the permeability-surface area product of the villus microcirculation are used in an analysis of glucose absorption in humans and rats, the concentrations of glucose predicted to be present at the basement membrane of the epithelium rise to values that exceed 100mM. If an increase in villus blood flow did not occur in proportion to the glucose absorption rate, glucose concentration in the tissue would rise to even higher levels. Our tentative estimates of glucose concentration within the epithelial cells suggest that without increases in blood flow and PS of the villus microcirculation the rising levels of intracellular glucose concentration would limit maximal rates of absorption. It would seem that in addition to events occurring in the epithelial cells, the absorption of glucose involves a co-ordinated microvascular response comparable to that occurring in skeletal muscle during exercise.
Journal of lipid research, 2015
The mechanisms by which LDLs and HDLs cross the vascular endothelium from plasma into interstitia... more The mechanisms by which LDLs and HDLs cross the vascular endothelium from plasma into interstitial fluid are not understood, and have never been studied in humans in vivo. We determined whether the plasma-to-lymph clearance rates of LDL and HDL conform with those predicted by passive ultrafiltration through intercellular pores, or if it is necessary to invoke an active process such as receptor-mediated transcytosis. Plasma and afferent peripheral lymph were collected under steady-state conditions from 30 healthy men, and assayed for seven globular proteins of molecular radii 2.89-8.95 nm, complement C3, and apo AI, apo AII, and apo B. Plasma-to-lymph clearance rates of the seven proteins fitted the relation expected for molecules of their size when transported through two populations of pores of radius 4.95 and 20.1 nm. The same model parameters were then found to accurately predict the clearance rates of both HDL and LDL. The apparent clearance of complement C3, previously shown to...
Microcirculation, 2014
To evaluate the dynamics of skin microvascular blood flow (BF) and tissue oxygenation parameters ... more To evaluate the dynamics of skin microvascular blood flow (BF) and tissue oxygenation parameters (OXY) measured simultaneously at the same site using a combined non-invasive BF+OXY+temperature probe. Skin BF, oxygenated (oxyHb) and deoxygenated (deoxyHb) haemoglobin and mean oxygen saturation (SO2 ) were measured in 50 healthy volunteers at rest and during perturbation of local blood flow by post-occlusive reactive hyperaemia, sympathetic nervous system-mediated vasoconstriction (deep inspiratory breath-hold) and local skin warming. Signals were analysed in time and frequency domains. The relationship between BF and SO2 over the range of flows investigated was described by a non-linear equation with an asymptote for SO2 of 84% at BF &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;50 PU. SO2 was independently associated with BF, skin temperature, BMI and age, which together identified 59% of the variance in SO2 (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.0001). Fourier analysis revealed periodic low frequency fluctuations in both BF and SO2 , attributable to endothelial (~0.01 Hz), neurogenic (~0.04 Hz) and myogenic (~0.1 Hz) flow motion activity. The frequency coherence between the BF and SO2 signals was greatest in the endothelial and neurogenic frequency bands. The simultaneous evaluation of microvascular blood flow and oxygenation kinetics in healthy skin provides a platform from which to investigate microvascular impairment in the skin and more generally the pathogenesis of microvascular disease.
Microcirculation, 2012
In this issue of Microcirculation, Wagner, Modla, Hossler and Czmmek describe the use of electron... more In this issue of Microcirculation, Wagner, Modla, Hossler and Czmmek describe the use of electron tomography to visualize the three-dimensional arrangement of small endothelial vesicles and caveolae of muscle capillaries. Their images show the wellknown clusters of fused vesicles communicating with caveolae at the luminal and abluminal surfaces. The advantages of electron tomography are shown by well resolved images of single cytoplasmic vesicles separate from fused vesicle clusters and also by occasional chains of fused vesicles forming trans-endothelial channels. Twenty five to thirty years ago the existence of both trans-endothelial channels and single unattached vesicles was disputed. Also, since some single vesicles and all of the transendothelial channels are labeled with a lanthanide tracer present in the perfusate at the time of fixation, this evidence once again raises the question of whether vesicles have a role in vascular permeability to macromolecules. This brief review describes the origin of the vesicle controversy, some of the more recent evidence for and against the participation of vesicles in macromolecular transport and considers some criticisms of ultrastructural evidence for vesicular transport that still require answers.
Microcirculation, 1997
The Editor gratefully acknoruledges Projkssor Charles Michel for his preparation of this tribute.
Cardiovascular Research, 2010
Microvascular fluid exchange (flow J(v)) underlies plasma/interstitial fluid (ISF) balance and oe... more Microvascular fluid exchange (flow J(v)) underlies plasma/interstitial fluid (ISF) balance and oedematous swelling. The traditional form of Starling&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s principle has to be modified in light of insights into the role of ISF pressures and the recognition of the glycocalyx as the semipermeable layer of endothelium. Sum-of-forces evidence and direct observations show that microvascular absorption is transient in most tissues; slight filtration prevails in the steady state, even in venules. This is due in part to the inverse relation between filtration rate and ISF plasma protein concentration; ISF colloid osmotic pressure (COP) rises as J(v) falls. In some specialized regions (e.g. kidney, intestinal mucosa), fluid absorption is sustained by local epithelial secretions, which flush interstitial plasma proteins into the lymphatic system. The low rate of filtration and lymph formation in most tissues can be explained by standing plasma protein gradients within the intercellular cleft of continuous capillaries (glycocalyx model) and around fenestrations. Narrow breaks in the junctional strands of the cleft create high local outward fluid velocities, which cause a disequilibrium between the subglycocalyx space COP and ISF COP. Recent experiments confirm that the effect of ISF COP on J(v) is much less than predicted by the conventional Starling principle, in agreement with modern models. Using a two-pore system model, we also explore how relatively small increases in large pore numbers dramatically increase J(v) during acute inflammation.
British Journal of Pharmacology, 1989
1. We have investigated the effects of a standardised mixture of hydroxyethyl rutosides (HR) upon... more 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.