PAF- and bradykinin-induced hyperpermeability of rat venules is independent of actin-myosin contraction

Abstract

. PAF-and bradykinin-induced hyperpermeability of rat venules is independent of actin-myosin contraction. Am J Physiol Heart Circ Physiol 285: H406-H417, 2003. First published March 20, 2003 10.1152/ajpheart. 00021.2003.-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 (L p) was measured to monitor hyperpermeability response to the platelet-activating factor (PAF) 1-O-hexadecyl-2-acetylsn-glycero-3-phosphocholine or bradykinin. Perfusion withϪ7 cm/(s ⅐ cmH2O)] that peaked in 8.9 Ϯ 0.5 min and then returned toward control L p [1.6 Ϯ 0.1 ϫ 10 Ϫ7 cm/(s ⅐ cmH2O)]. Reconstruction of venular segments with the use of transmission electron microscopy of serial sections confirmed that PAF induces paracellular inflammatory gaps. Specific inhibition of myosin light chain kinase (MLCK) with 1-10 M 1-(5-iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML-7) failed to block the PAF L p response or change the time-to-peak Lp. ML-7 reduced baseline Lp 50% at 40 min of pretreatment. ML-7 also increased the rate of recovery from PAF hyperpermeability measured as the decrease of half-time of recovery from 4.8 Ϯ 0.7 to 3.2 Ϯ 0.3 min. Inhibition of myosin ATPase with 5-20 mM 2,3-butanedione 2-monoxime also failed to alter the hyperpermeability response to PAF. Similar results were found using ML-7 to modulate responses. These experiments indicate that an actin-myosin contractile mechanism modulated by MLCK does not contribute significantly to the robust initial increase in permeability of rat venular microvessels exposed to two common inflammatory mediators. The results are consistent with paracellular gap formation by local release of endothelialendothelial cell adhesion structures in the absence of contraction by the actin-myosin network.bradykinin; platelet-activating factor; inflammatory gaps; vascular endothelium; ML-7; myosin light chain kinase

Angiopoietin-1 decreases plasma leakage by reducing number and size of endothelial gaps in venules

“…The classic studies of Majno and Palade (24) implicated endothelial gaps in plasma leakage from inflamed venules. Results of many subsequent studies are consistent with that view (1,3,16,17). The presence of endothelial gaps at sites of particulate tracer leakage and the extravasation of tracers from inflamed vessels after fixation provide further evidence for openings in the endothelium that permit extravasation driven by hydraulic pressure gradients rather than transcellular transport (26).…”

“…This action of bradykinin is mediated via B 2 -receptor signaling in endothelial cells. Leakage is restricted to postcapillary venules and is thought to result from the formation of gaps between endothelial cells (1,12,17).…”

“…As endothelial gaps are reported to have an average size of ϳ500 nm (26), they appear to be a reasonable pathway for extravasation of microspheres in the system we studied. A conventional method for studying endothelial gaps involves electron microscopy (1,3,16,17,24). This approach has the attribute of high resolution but may be limited by the small regions sampled.…”

TLR4 Signaling Is Coupled to SRC Family Kinase Activation, Tyrosine Phosphorylation of Zonula Adherens Proteins, and Opening of the Paracellular Pathway in Human Lung Microvascular Endothelia

“…Agonists, such as histamine (61), thrombin (62), bradykinin, and platelet-activating factor (63), provoke immediate changes in permeability. However, agonists, such as TNF-␣ (10), IL-1 (64), thrombospondin-1 (37), and SPARC (38), each elicit a delayed response.…”

Vascular Integrity Mediated by Vascular Endothelial Cadherin and Regulated by Sphingosine 1-Phosphate and Angiopoietin-1

“…32 In contrast to thrombin, bradykinin induces vascular permeability independently of MLC-K and Rho kinase. 33 Histamine released from mast cells also transiently increases permeability, compared with thrombin, by activating H1 receptors expressed on ECs. 34 Platelet-activating factor augments vascular permeability independently of the actin-myosin contraction, similar to bradykinin 33 (Figure 3).…”