Plasmalemmal vesicles represent the large pore system of continuous microvascular endothelium

1993 ◽  
Vol 265 (2) ◽  
pp. H725-H733 ◽  
Author(s):  
D. Predescu ◽  
G. E. Palade
Keyword(s):  
Intercellular Junctions ◽  
Pore System ◽  
Microvascular Endothelium ◽  
Plasmalemmal Vesicles ◽  
Morphological Studies ◽  
Large Pore ◽  
In Transit

In the capillary physiology literature, molecules and particles larger than 10 nm are assumed to leave the plasma mostly through large pores located at the level of intercellular junctions in microvessels lined with a continuous endothelium. In morphological studies of similar microvessels, outgoing particles > 10 nm were detected in endothelial plasmalemmal vesicles not in intercellular junctions. Because the probes may not be found in transit through the junctions because they may be swept away by strong currents generated by Starling forces, we have examined a large number of junctions in arteriolar, capillary, and venular segments of bipolar vascular fields of mouse diaphragms collected after perfusion with large pore probes. The results presented in this study indicate that 1) the perfused probes accumulate in the luminal introits of the junctions as filtration residues that decrease in size and frequency from arterioles to venules, and 2) large pore probes move across the endothelium exclusively through plasmalemmal vesicles.

scholarly journals Binding and transcytosis of glycoalbumin by the microvascular endothelium of the murine myocardium: evidence that glycoalbumin behaves as a bifunctional ligand.

1988 ◽  
Vol 107 (5) ◽  
pp. 1729-1738 ◽  
Author(s):  
D Predescu ◽  
M Simionescu ◽  
N Simionescu ◽  
G E Palade
Keyword(s):  
Intercellular Junctions ◽  
Concomitant Administration ◽  
Multivesicular Bodies ◽  
Microvascular Endothelium ◽  
Coated Pits ◽  
Gold Complexes ◽  
Plasmalemmal Vesicles ◽  
Bifunctional Ligand ◽  
Albumin Molecule

The binding and transport of glycoalbumin (gA) by the endothelium of murine myocardial microvessels were studied by perfusing in situ 125I-gA or gA-gold complexes (gA-Au) and examining the specimens by radioassays and EM, respectively. After a 3-min perfusion, the uptake of radioiodinated gA is 2.2-fold higher than that of native albumin; it is partially (approximately 55%) competed by either albumin or D-glucose, and almost completely abolished by the concomitant administration of both competitors or by gA. D-mannose and D-galactose are not effective competitors. Unlike albumin-gold complexes that bind restrictively to plasmalemmal vesicles, gA-Au labels the plasma-lemma proper, plasmalemmal vesicles open on the lumen, and most coated pits. Competing albumin prevents gA-Au binding to the membrane of plasmalemmal vesicles, while glucose significantly reduces the ligand binding to plasmalemma proper. Competition with albumin and glucose gives additive effects. Transcytosis of gA-Au, already detected at 3 min, becomes substantial by 30 min. No tracer exit via intercellular junctions was detected. gA-Au progressively accumulates in multivesicular bodies. The results of the binding and competition experiments indicate that the gA behaves as a bifunctional ligand which is recognized by two distinct binding sites: one, located on the plasma membrane, binds as a lectin the glucose residues of gA; whereas the other, confined to plasmalemmal vesicles, recognizes presumably specific domains of the albumin molecule.

scholarly journals INTESTINAL CAPILLARIES

1969 ◽  
Vol 41 (1) ◽  
pp. 33-58 ◽  
Author(s):  
F. Clementi ◽  
G. E. Palade
Keyword(s):  
Electron Microscopy ◽  
Horseradish Peroxidase ◽  
Intestinal Mucosa ◽  
Intercellular Junctions ◽  
Post Injection ◽  
Pore System ◽  
Blood Capillaries ◽  
Large Pore ◽  
Small Pore ◽  
Histochemical Procedure

Horseradish peroxidase (mol. diam. ≃50 A) and ferritin (mol. diam. ≃110 A) were used as probe molecules for the small and large pore system, respectively, in blood capillaries of the intestinal mucosa of the mouse. Peroxidase distribution was followed in time, after intravenous injection, by applying the Graham-Karnovsky histochemical procedure to aldehyde-fixed specimens. The tracer was found to leave the plasma rapidly and to reach the pericapillary spaces 1 min post injection. Between 1 min and 1 min 30 sec, gradients of peroxidase reaction product could be demonstrated regularly around the capillaries; their highs were located opposite the fenestrated parts of the endothelium. These gradients were replaced by even distribution past 1 min 30 sec. Ferritin, followed directly by electron microscopy, appeared in the pericapillary spaces 3–4 min after i.v. injection. Like peroxidase, it initially produced transient gradients with highs opposite the fenestrated parts of the endothelium. For both tracers, there was no evidence of movement through intercellular junctions, and transport by plasmalemmal vesicles appeared less efficient than outflow through fenestrae. It is concluded that, in the blood capillaries of the inintestinal mucosa, the diaphragms of the endothelial fenestrae contain the structural equivalents of the small pore system. The large pore system seems to be restricted to a fraction of the fenestral population which presumably consists of diaphragm-free or diaphragm-deficient units.

Transport of insulin and albumin by the microvascular endothelium of the rete mirabile

1996 ◽  
Vol 109 (7) ◽  
pp. 1857-1864 ◽  
Author(s):  
M. Bendayan ◽  
E.A. Rasio
Keyword(s):  
Serum Proteins ◽  
Protein A ◽  
Simultaneous Detection ◽  
Intercellular Junctions ◽  
Buffer Solution ◽  
Microvascular Endothelium ◽  
Double Labeling ◽  
Plasmalemmal Vesicles ◽  
Rete Mirabile ◽  
Paracellular Diffusion

Vascular permeability for albumin and insulin in the continuous capillary network of the rete mirabile of the eel swimbladder was evaluated by ultrastructural immunocytochemistry and countercurrent perfusion experiments. Upon perfusion of the rete capillaries with a buffer solution containing albumin and insulin, these serum proteins were revealed at the electron microscope level, by the Protein A-gold immunocytochemical technique on a post-embedding step. For the simultaneous detection of both proteins, the double labeling technique with different sized gold particles was used. Furthermore, labeling was performed with the mixture of anti-albumin and anti-insulin anti-bodies. The labelings obtained were morphometrically evaluated and demonstrate that: (1) serum proteins such as albumin and insulin are transported by the endothelial cells through their plasmalemmal vesicular system; (2) insulin is transported preferentially to albumin; and (3) this transport involves different populations of plasmalemmal vesicles. Measurements of diffusion permeability coefficients have confirmed the preferential transport of insulin, its coefficient being higher than that of albumin. Conversely, when compared to that of insulin or sucrose, which are assumed to be markers of the paracellular diffusion, it was found to be much lower, indicating that transcytosis through the vesicular system is less efficient than diffusion along the intercellular junctions. These results indicate that transcytosis of insulin and albumin occurs via different sets of plasmalemmal vesicles, probably through receptor-mediated mechanisms, and that the overall rate of transport across the rete capillaries, with respect to paracellular diffusion, is higher for insulin than for albumin.

scholarly journals PERMEABILITY OF MUSCLE CAPILLARIES TO EXOGENOUS MYOGLOBIN

1973 ◽  
Vol 57 (2) ◽  
pp. 424-452 ◽  
Author(s):  
Nicolae Simionescu ◽  
Maia Simionescu ◽  
George E. Palade
Keyword(s):  
Gel Filtration ◽  
Intercellular Junctions ◽  
Cell Periphery ◽  
Pore System ◽  
Regional Heterogeneity ◽  
Plasmalemmal Vesicles ◽  
Small Pore ◽  
Perinuclear Cytoplasm ◽  
Muscle Capillaries

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

scholarly journals PERMEABILITY OF INTESTINAL CAPILLARIES

1972 ◽  
Vol 53 (2) ◽  
pp. 365-392 ◽  
Author(s):  
Nicolae Simionescu ◽  
Maia Simionescu ◽  
George E. Palade
Keyword(s):  
Intercellular Junctions ◽  
Liver Glycogen ◽  
Pore System ◽  
Concentration Gradients ◽  
Good Definition ◽  
Plasmalemmal Vesicles ◽  
Tracer Particles ◽  
One Step ◽  
Dynamic Structures ◽  
Capillary Walls

The pathway followed by macromolecules across the wall of visceral capillaries has been studied by using a set of tracers of graded sizes, ranging in diameter from 100 A (ferritin) to 300 A (glycogen). Polysaccharide particles, i.e. dextran 75 (mol wt ∼75,000; diam ∼125 A), dextran 250 (mol wt 250,000; diam ∼225 A), shellfish glycogen (diam ∼200 A) and rabbit liver glycogen (diam ∼300 A), are well tolerated by Wistar-Furth rats and give no vascular reactions ascribable to histamine release. Good definition and high contrast of the tracer particles were obtained in a one-step fixation—in block staining of the tissues by a mixture containing aldehydes, OsO4 and lead citrate in phosphate or arsenate buffer, pH 7.4, followed by lead staining of sections. The glycogens and dextrans used move out of the plasma through the fenestrae and channels of the endothelium relatively fast (3–7 min) and create in the pericapillary spaces transient (2–5 min) concentration gradients centered on the fenestrated sectors of the capillary walls. The tracers also gained access to the plasmalemmal vesicles, first on the blood front and subsequently on the tissue front of the endothelium. The particles are temporarily retained by the basement membrane. No probe moved through the intercellular junctions. It is concluded that, in visceral capillaries, the fenestrae, channels, and plasmalemmal vesicles, viewed as related parts in a system of dynamic structures, are the structural equivalent of the large pore system.

scholarly journals Rings of membrane sterols surround the openings of vesicles and fenestrae, in capillary endothelium.

1983 ◽  
Vol 97 (5) ◽  
pp. 1592-1600 ◽  
Author(s):  
N Simionescu ◽  
F Lupu ◽  
M Simionescu
Keyword(s):  
Plasma Membrane ◽  
Cell Membrane ◽  
Cell Surface ◽  
Freeze Fracture ◽  
Short Exposure ◽  
Capillary Endothelium ◽  
Anionic Sites ◽  
Microvascular Endothelium ◽  
Coated Pits ◽  
Plasmalemmal Vesicles

We investigated the distribution of sterols in the cell membrane of microvascular endothelium (mouse pancreas, diaphragm, brain, heart, lung, kidney, thyroid, adrenal, and liver) with the polyene antibiotic filipin, which reportedly has binding specificity for free 3-beta-hydroxysterols. In some experiments, concomitantly, cell-surface anionic sites were detected with cationized ferritin. Vessels were perfused in situ with PBS, followed by light fixation and filipin administration for 10 to 60 min. Tissues were further processed for thin-section and freeze-fracture electron microscopy. Short exposure (10 min) to filipin-glutaraldehyde solution resulted in the initial appearance, on many areas, of rings of characteristic filipin-sterol complexes within the rim surrounding stomata of most plasmalemmal vesicles, transendothelial channels, and fenestrae. Such rings were absent from the rims of the large openings of the sinusoid endothelium (liver, adrenal), coated pits and phagocytic vacuoles. After longer exposure (30-60 min), filipin-sterol complexes labeled randomly the rest of plasma membrane (except for coated pits, and partially the interstrand areas of junctions), and also marked most plasmalemmal vesicles. These peristomal rings of sterols were displayed mostly on the P face, and, at their full development, consisted of 6-8 units around a vesicle stoma, and 10-12 units around a fenestra. At their level, the intramembranous particles and the cell surface anionic sites were virtually excluded. Peristomal rings of sterols were also detected on the plasma membrane of pericytes and smooth muscle cells of the microvascular wall, which otherwise were poorly labeled with filipin-sterol complexes as compared to endothelial plasmalemma. It is presumed that the peristomal rings of cholesterol may represent important contributors to the local transient stabilization of plasma membrane and to the phase separation between cell membrane and vesicle membrane at a certain stage of their fusion/fission process.

Plasmalemmal vesicles function as transcytotic carriers for small proteins in the continuous endothelium

1997 ◽  
Vol 272 (2) ◽  
pp. H937-H949 ◽  
Author(s):  
S. A. Predescu ◽  
D. N. Predescu ◽  
G. E. Palade
Keyword(s):  
Capillary Permeability ◽  
Pore System ◽  
Plasmalemmal Vesicles ◽  
Small Proteins ◽  
Structural Identity ◽  
Heart Perfusion ◽  
Small Pore ◽  
Vesicular Carriers ◽  
Tissue Fractionation

We investigated the location and the structural identity of the small pore system, postulated by the pore theory of capillary permeability, using a murine heart perfusion system and small protein molecules as preferential probes for the small pores. Dinitrophenylated proteins were perfused in situ in the absence and in the presence of N-ethylmaleimide (NEM), a reagent known to interfere with membrane fusion of vesicular carriers with their target membranes. The exit pathways of the tracers from vascular lumina to the interstitia were followed by immunoelectron microscopy and by tissue fractionation biochemistry to quantitate their transport and to estimate the extent of transport inhibition by NEM. After 5 min of perfusion, all tracers used were found essentially restricted to plasmalemmal vesicles (PVs) within the endothelium and NEM inhibited their transport by 80-85%. The transport of [14C]inulin and [14C]sucrose, assumed to follow the paracellular pathway, was marginally affected by NEM. These findings indicate that PVs function as structural equivalents of the small pore system for molecules >2 nm in diameter.

scholarly journals HPM‐16, a New Stable Interrupted Zeolite with a Multidimensional Mixed Medium‐Large Pore System Containing Supercages

2021 ◽  
Author(s):  
Zihao Rei Gao ◽  
Salvador R. G. Balestra ◽  
Jian Li ◽  
Miguel A. Camblor
Keyword(s):  
Pore System ◽  
Large Pore ◽  
Mixed Medium
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