We hypothesized that ultrafiltrate crossing the luminal endothelial glycocalyx through infrequent discontinuities (gaps) in tight junction (TJ) strand of clefts reduces albumin diffusive flux from tissue into ‘protected region’ cleft on side TJ. Thus, effective oncotic pressure difference (σ□π) opposing filtration is greater than measured between lumen and interstitial fluid. To test this we σ□π across rat mesenteric microvessels perfused with (50 mg ml −1 ) without at same concentration...

Two methods are described for measuring the filtration coefficient of individually perfused frog mesenteric capillaries. Both involve perfusion capillaries via a micropipette with solution in which small number human red cells suspended. After short period perfusion, capillary is occluded at point some 500 µm or more downstream from cannulation. Movements isolated system interpreted to be consequence fluid movements across wall. The determined either (method I) series different rates...

We have extended the use of a microscope densitometric technique [Am. J. Physiol. 245 (Heart Circ. 14): H495-H505, 1983] to measure solute permeability coefficients (Pa) fluorescently labeled solutes in single perfused capillaries frog mesentery. The method enables transcapillary flux larger than 10,000 mol wt be measured under conditions where forces that determine both and water flows across capillary wall are known. Pa for alpha-lactalbumin (mol 14,176, Stokes radius 2.02 nm) increased...

These experiments report the first direct measurement of microvessel permeability coefficients after exposure to vascular endothelial growth factor (VEGF). The Landis technique was extended enable resistance wall water flow, hydraulic conductivity (Lp), on same in frog mesentery during initial VEGF (acute) and 24 72 h (chronic). Control measurements Lp showed no change either acutely or chronically. Exposure 1 nM rapidly transiently increased within 30 s (to 7.8-fold greater than baseline...

We tested the hypothesis that vascular endothelial growth factor (VEGF) increases microvascular permeability by increasing calcium influx into cells forming vessel walls. measured microvessel hydraulic conductivity (Lp) in isolated perfused MS-222-anesthetized frog mesenteric microvessels during perfusion with VEGF under conditions attenuate influx. increased Lp a second successive same 7.8-fold, which was not significantly different from brought about an initial application of (5.0-fold)....

We tested the hypothesis that effective oncotic force opposes fluid filtration across microvessel wall is local pressure difference endothelial surface glycocalyx and not global between plasma tissue. In single frog mesenteric microvessels perfused superfused with solutions containing 50 mg/ml albumin, exerted was significantly different from measured when perfusate alone contained albumin at mg/ml. Measurements were made during transient steady-state capillary pressures 10 35 cmH 2 O. A...

We tested the hypothesis that increased endothelial cell adenosine 3′,5′-cyclic monophosphate (cAMP) decreases microvascular permeability in vivo. The effects of cAMP-specific phosphodiesterase type IV inhibition and adenylate cyclase activation on hydraulic conductivity ( L p ) were investigated intact individual capillaries postcapillary venules mesentery pithed frogs Rana pipiens). Treatment with rolipram (10 μM) forskolin (5 for 25 min decreased to 37% control. Rolipram alone also...

Our previous experiments indicated that GTPases, other than RhoA, are important for the maintenance of endothelial barrier integrity in both intact microvessels rats and mice cultured mouse myocardial (MyEnd) cell monolayers ( J Physiol 539: 295–308, 2002). In present study, we inhibited GTPase Rac by Clostridium sordellii lethal toxin (LT) investigated relation between degree inhibition glucosylation increased permeability. rat venular microvessels, LT (200 ng/ml) hydraulic conductivity...

1. Individual capillaries of the transilluminated frog mesentery have been perfused with suspensions human red cells in Ringer solution containing 1-0 g albumin 100 ml.-1. The outer surface has washed normal and solutions made hypertonic by addition one following solutes: sodium chloride (100 m-mole. 1.-1); urea m-mole.1.-1); sucrose (20-50 cyanocobalamin (8-5 1.-1). temperature was between 14 16 degrees C all experiments. 2. Wtih superfused Ringer, filtration coefficient determined from...

Abstract Objective S1P was found to protect the ESG by inhibiting MMP activity‐dependent shedding of in cultured endothelial cell studies. We aimed further test that contributes maintenance normal vascular permeability protecting intact microvessels. Methods quantified post‐capillary venules rat mesentery and measured albumin presence absence 1 μ M S1P. also inhibitors compared with those predicted a transport model for inter‐endothelial cleft. Results S1P, fluorescence intensity FITC...

Previous experiments using cultured endothelial monolayers indicate that Rho-family small GTPases are involved in modulation of monolayer permeability by regulating assembly the cellular actin filament scaffold, activity myosin-based contractility and junctional distribution Ca2+-dependent cell adhesion molecule, VE-cadherin. We investigated these mechanisms both cells (from porcine pulmonary artery mouse heart) vascular endothelium situ (mouse aorta, individually perfused venular...

We tested the hypothesis that equilibrium between F- and G-actin in endothelial cells modulates integrity of actin cytoskeleton is important for maintenance barrier functions vivo vitro. used actin-depolymerizing agent cytochalasin D jasplakinolide, an filament (F-actin) stabilizing promoting substance, to modulate cytoskeleton. Low doses jasplakinolide (0.1 microM), which we have previously shown reduce permeability-increasing effect D, had no influence on resting permeability...

We tested the hypothesis that acutely induced hyperpermeability is dependent on actin-myosin contractility by using individually perfused mesentery venules of pentobarbital-anesthetized rats. Venule hydraulic conductivity (Lp) was measured to monitor response platelet-activating factor (PAF) 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine or bradykinin. Perfusion with PAF (10 nM) a robust transient high Lp [24.3 +/- 1.7 x 10-7 cm/(s.cmH2O)] peaked in 8.9 0.5 min and then returned toward...

Experiments in cultured endothelial cell monolayers demonstrate that increased intracellular cAMP strongly inhibits the acute permeability responses by both protein kinase A (PKA)-dependent and -independent pathways. The contribution of PKA-independent pathways to anti-inflammatory mechanisms intact mammalian microvessels has not been systematically investigated. We evaluated role cAMP-dependent activation exchange activated (Epac), a guanine nucleotide factor for small GTPase Rap1, rat...

Removal of plasma proteins from perfusates increases vascular permeability. The common interpretation the action albumin is that it forms part permeability barrier by electrostatic binding to endothelial glycocalyx. We tested alternate hypothesis removal perfusate in rat venular microvessels decreased availability sphingosine-1-phosphate (S1P), which normally carried bound and lipoproteins required maintain stable baseline barriers ( Am J Physiol Heart Circ 303: H825–H834, 2012). Red blood...

We reported previously that increasing cAMP levels in endothelial cells attenuated ATP-induced increases hydraulic conductivity ( L p ), and the activation of cGMP-dependent pathways was a necessary step to increase response inflammatory mediators. The aim present study evaluate role basal microvessel permeability under resting conditions cross talk between cAMP- signaling mechanisms regulation stimulated conditions, using individually perfused microvessels from frog rat mesenteries. found...