Counter regulatory effects of PKCbetaII and PKCdelta on coronary endothelial permeability

Imaging and Analysis of the Dynamics of Filamentous Actin Structures in Live Endothelial Cells

The ability to view and record the movements of subcellular structures is a powerful tool that has accelerated the discovery and understanding of signaling mechanisms that control microvascular functions such as the control of endothelial permeability. Advances in molecular biology over the past few decades have facilitated the generation of fusion proteins in which fluorescent reporters based upon the structure of green fluorescent protein can be linked to proteins found in human endothelial cells, such as VE-cadherin or β-actin. These fusion proteins have been found to incorporate into structures alongside their native protein counterparts, allowing the dynamic visualization of how these subcellular structures are modified when cells are challenged with stimuli such as inflammatory mediators. The result of such studies has been a much more advanced view of the complex mechanisms by which endothelial cells maintain barrier properties than previously obtained by only viewing fixed cells labeled by immunofluorescence. Here, we describe our protocols that we have used to view the dynamics of actin filaments using time-lapse microscopy to record endothelial cells expressing GFP-actin and the analysis tools available to quantify dynamics of subcellular structures.

PKCδ regulates the vascular biology in diabetic atherosclerosis

Diabetes mellitus, known for its complications, especially vascular complications, is becoming a globally serious social problem. Atherosclerosis has been recognized as a common vascular complication mechanism in diabetes. The diacylglycerol (DAG)-protein kinase C (PKC) pathway plays an important role in atherosclerosis. PKCs can be divided into three subgroups: conventional PKCs (cPKCs), novel PKCs (nPKCs), and atypical PKCs (aPKCs). The aim of this review is to provide a comprehensive overview of the role of the PKCδ pathway, an isoform of nPKC, in regulating the function of endothelial cells, vascular smooth muscle cells, and macrophages in diabetic atherosclerosis. In addition, potential therapeutic targets regarding the PKCδ pathway are summarized. Video Abstract.

Endothelial Protrusions in Junctional Integrity and Barrier Function

Endothelial cells of the microcirculation form a semi-permeable diffusion barrier between the blood and tissues. This permeability of the endothelium, particularly in the capillaries and postcapillary venules, is a normal physiological function needed for blood-tissue exchange in the microcirculation. During inflammation, microvascular permeability increases dramatically and can lead to tissue edema, which in turn can lead to dysfunction of tissues and organs. The molecular mechanisms that control the barrier function of endothelial cells have been under investigation for several decades and remain an important topic due to the potential for discovery of novel therapeutic strategies to reduce edema. This review highlights current knowledge of the cellular and molecular mechanisms that lead to endothelial hyperpermeability during inflammatory conditions associated with injury and disease. This includes a discussion of recent findings demonstrating temporal protrusions by endothelial cells that may contribute to intercellular junction integrity between endothelial cells and affect the diffusion distance for solutes via the paracellular pathway.

Ischemia/Reperfusion-Induced Translocation of PKCβII to Mitochondria as an Important Mediator of a Protective Signaling Mechanism in an Ischemia-Resistant Region of the Hippocampus

Emerging reports indicate that activated PKC isoforms that translocate to the mitochondria are pro- or anti-apoptotic to mitochondrial function. Here, we concentrate on the role of PKCβ translocated to mitochondria in relation to the fate of neurons following cerebral ischemia. As we have demonstrated previously ischemia/reperfusion injury (I/R) results in translocation of PKCβ from cytoplasm to mitochondria, but only in ischemia-resistant regions of the hippocampus (CA2-4, DG), we hypothesize that this translocation may be a mediator of a protective signaling mechanism in this region. We have therefore sought to demonstrate a possible relationship between PKCβII translocation and ischemic resistance of CA2-4, DG. Here, we reveal that I/R injury induces a marked elevation of PKCβII protein levels, and consequent enzymatic activity, in CA2-4, DG in the mitochondrial fraction. Moreover, the administration of an isozyme-selective PKCβII inhibitor showed inhibition of I/R-induced translocation of PKCβII to the mitochondria and an increase in neuronal death following I/R injury in CA1 and CA2-4, DG in both an in vivo and an in vitro model of ischemia. The present results suggest that PKCβII translocated to mitochondria is involved in providing ischemic resistance of CA2-4, DG. However, the exact mechanisms by which PKCβII-mediated neuroprotection is achieved are in need of further elucidation.

Regulation of pulmonary endothelial barrier function by kinases

The pulmonary endothelium is the target of continuous physiological and pathological stimuli that affect its crucial barrier function. The regulation, defense, and repair of endothelial barrier function require complex biochemical processes. This review examines the role of endothelial phosphorylating enzymes, kinases, a class with profound, interdigitating influences on endothelial permeability and lung function.

Subcellular proteomic approach for identifying the signaling effectors of protein kinase C-β₂ under high glucose conditions in human umbilical vein endothelial cells

The high glucose‑induced activation of protein kinase C‑β2 (PKC‑β2) has an essential role in the pathophysiology of diabetes‑associated vascular disease. In the present study, human umbilical vein endothelial cells (HUVECs) were cultured in high and normal glucose conditions prior to being infected with a recombinant adenovirus to induce the overexpression of PKC‑β2. The activity of PKC‑β2 was also decreased using a selective PKC‑β2 inhibitor. A series of two‑dimensional electrophoresis images detected ~800 spots in the nuclei, and ~600 spots in the cytosol. Following intra‑ and inter‑group cross‑matching, 38 significantly altered spots were identified as high glucose‑induced and PKC‑β2‑associated nuclear proteins. In addition to the observation that the regulation of key proteins involved in the nuclear factor (NF)‑κB signaling cascade occurred in the cytosol, various transcription factors, including peroxisome proliferator‑activated receptor δ (PPAR‑δ), were also altered in the nuclei. A human protein‑protein interaction network of potential connections of PKC‑β2‑associated proteins was constructed in the proteomics investigation using Biological General Repository for Interaction Datasets. The results indicated that PKC‑β2 may be involved in high glucose‑induced glucose and lipid crosstalk by regulating PPAR‑δ. In addition, NF‑κB inhibitor‑interacting Ras‑like protein 1 may be important in the PKC‑β2‑NF‑κB inhibitor‑NF‑κB signaling pathway in HUVECs under high‑glucose conditions.

Involvement of Protein Kinase C-δ in Vascular Permeability in Acute Lung Injury

Pulmonary edema is a major cause of mortality due to acute lung injury (ALI). The involvement of protein kinase C-δ (PKC-δ) in ALI has been a controversial topic. Here we investigated PKC-δ function in ALI using PKC-δ knockout (KO) mice and PKC inhibitors. Our results indicated that although the ability to produce proinflammatory mediators in response to LPS injury in PKC-δ KO mice was similar to that of control mice, they showed enhanced recruitment of neutrophils to the lung and more severe pulmonary edema. PKC-δ inhibition promoted barrier dysfunction in an endothelial cell layer in vitro, and administration of a PKC-δ-specific inhibitor significantly increased steady state vascular permeability. A neutrophil transmigration assay indicated that the PKC-δ inhibition increased neutrophil transmigration through an endothelial monolayer. This suggests that PKC-δ inhibition induces structural changes in endothelial cells, allowing extravasation of proteins and neutrophils.

Endothelial calcium dynamics, connexin channels and blood-brain barrier function

Situated between the circulation and the brain, the blood-brain barrier (BBB) protects the brain from circulating toxins while securing a specialized environment for neuro-glial signaling. BBB capillary endothelial cells exhibit low transcytotic activity and a tight, junctional network that, aided by the cytoskeleton, restricts paracellular permeability. The latter is subject of extensive research as it relates to neuropathology, edema and inflammation. A key determinant in regulating paracellular permeability is the endothelial cytoplasmic Ca(2+) concentration ([Ca(2+)]i) that affects junctional and cytoskeletal proteins. Ca(2+) signals are not one-time events restricted to a single cell but often appear as oscillatory [Ca(2+)]i changes that may propagate between cells as intercellular Ca(2+) waves. The effect of Ca(2+) oscillations/waves on BBB function is largely unknown and we here review current evidence on how [Ca(2+)]i dynamics influence BBB permeability.

Genetic disruption of protein kinase Cδ reduces endotoxin-induced lung injury

The pathogenesis of acute lung injury and acute respiratory distress syndrome is characterized by sequestration of leukocytes in lung tissue, disruption of capillary integrity, and pulmonary edema. PKCδ plays a critical role in RhoA-mediated endothelial barrier function and inflammatory responses. We used mice with genetic deletion of PKCδ (PKCδ(-/-)) to assess the role of PKCδ in susceptibility to LPS-induced lung injury and pulmonary edema. Under baseline conditions or in settings of increased capillary hydrostatic pressures, no differences were noted in the filtration coefficients (k(f)) or wet-to-dry weight ratios between PKCδ(+/+) and PKCδ(-/-) mice. However, at 24 h after exposure to LPS, the k(f) values were significantly higher in lungs isolated from PKCδ(+/+) than PKCδ(-/-) mice. In addition, bronchoalveolar lavage fluid obtained from LPS-exposed PKCδ(+/+) mice displayed increased protein and cell content compared with LPS-exposed PKCδ(-/-) mice, but similar changes in inflammatory cytokines were measured. Histology indicated elevated LPS-induced cellularity and inflammation within PKCδ(+/+) mouse lung parenchyma relative to PKCδ(-/-) mouse lungs. Transient overexpression of catalytically inactive PKCδ cDNA in the endothelium significantly attenuated LPS-induced endothelial barrier dysfunction in vitro and increased k(f) lung values in PKCδ(+/+) mice. However, transient overexpression of wild-type PKCδ cDNA in PKCδ(-/-) mouse lung vasculature did not alter the protective effects of PKCδ deficiency against LPS-induced acute lung injury. We conclude that PKCδ plays a role in the pathological progression of endotoxin-induced lung injury, likely mediated through modulation of inflammatory signaling and pulmonary vascular barrier function.

Activated protein C has a protective effect against myocardial I/R injury by improvement of endothelial function and activation of AKT1

Objectives

Activated protein C (APC) has a protective efficacy against ischemia-reperfusion (I/R) injury in several organs. The objective of this study was to investigate effect of APC in myocardium with possible mechanism.

Methods

We used regional and global myocardial I/R injury models of rats. They consisted of I/R injuries (1) by ligation of left coronary artery, or (2) using Langendorff apparatus. Langendorff was used to focus the mechanism of APC excluding coagulation cascade in a working heart. Each experiment had an APC group (n = 10) and a control group with normal saline (n = 10). Injections of these solutions into rats were performed 30 minutes before the planned-I/R injury. Cardiac performance after the procedure was evaluated by echocardiography or indices with Langendorff apparatus. Coronary flow (CF) was measured in the global I/R injury model. Western blotting was performed to detect the change of AKT1 signal in myocardium after global I/R injury.

Results

LV function improved significantly in the APC group: %EF at 2 weeks after procedure, 70.8%±4.5% vs. 56.5%±0.7%; APC vs. control; p<0.01. Percent LV development pressure (LVDP) also improved in the APC group significantly, 88.8%±45.3% vs. 28.1%±15.4%; APC vs. control; p<0.01. In APC group, %CF improved significantly, 88.5%±15.8% vs. 65.0%±13.4%; APC vs. control; p<0.01. It was enhanced significantly when acetylcholine was administered; % CF: 103.5%±9.9% vs. 87.0%±12.1%; APC vs. control; p<0.05. Western blotting revealed that APC significantly induced activation of phosphorylated AKT1 in myocardium (p<0.05).

Conclusions

APC has a novel effect to protect myocardium and cardiac performance against I/R injury through improvement of endothelial function and activation of AKT1.

Myosin light chain kinase signaling in endothelial barrier dysfunction

Microvascular barrier dysfunction is a serious problem that occurs in many inflammatory conditions, including sepsis, trauma, ischemia-reperfusion injury, cardiovascular disease, and diabetes. Barrier dysfunction permits extravasation of serum components into the surrounding tissue, leading to edema formation and organ failure. The basis for microvascular barrier dysfunction is hyperpermeability at endothelial cell-cell junctions. Endothelial hyperpermeability is increased by actomyosin contractile activity in response to phosphorylation of myosin light chain by myosin light chain kinase (MLCK). MLCK-dependent endothelial hyperpermeability occurs in response to inflammatory mediators (e.g., activated neutrophils, thrombin, histamine, tumor necrosis factor alpha, etc.), through multiple cell signaling pathways and signaling molecules (e.g., Ca(++) , protein kinase C, Src kinase, nitric oxide synthase, etc.). Other signaling molecules protect against MLCK-dependent hyperpermeability (e.g., sphingosine-1-phosphate or cAMP). In addition, individual MLCK isoforms play specific roles in endothelial barrier dysfunction, suggesting that isoform-specific inhibitors could be useful for treating inflammatory disorders and preventing multiple organ failure. Because endothelial barrier dysfunction depends upon signaling through MLCK in many instances, MLCK-dependent signaling comprises multiple potential therapeutic targets for preventing edema formation and multiple organ failure. The following review is a discussion of MLCK-dependent mechanisms and cell signaling events that mediate endothelial hyperpermeability.

Low extracellular Ca2+ conditions induce an increase in brain endothelial permeability that involves intercellular Ca2+ waves

The intracellular calcium concentration ([Ca(2+)](i)) is an important factor determining the permeability of endothelial barriers including the blood-brain barrier (BBB). However, nothing is known concerning the effect of spatially propagated intercellular Ca(2+) waves (ICWs). The propagation of ICWs relies in large part on channels formed by connexins that are present in endothelia. We hypothesized that ICWs may result in a strong disturbance of endothelial function, because the [Ca(2+)](i) changes are coordinated and involve multiple cells. Thus, we aimed to investigate the effect of ICWs on endothelial permeability. ICW activity was triggered in immortalized and primary brain endothelial cells by lowering the extracellular Ca(2+) concentration. Low extracellular Ca(2+) increased the endothelial permeability and this was significantly suppressed by buffering [Ca(2+)](i) with BAPTA-AM, indicating a central role of [Ca(2+)](i) changes. The endothelial permeability increase was furthermore inhibited by the connexin channel blocking peptide Gap27, which also blocked the ICWs, and by inhibiting protein kinase C (PKC), Ca(2+)/calmodulin-dependent kinase II (CaMKII) and actomyosin contraction. We compared these observations with the [Ca(2+)](i) changes and permeability alterations provoked by the inflammatory agent bradykinin (BK), which triggers oscillatory [Ca(2+)](i) changes without wave activity. BK-associated [Ca(2+)](i) changes and the endothelial permeability increase were significantly smaller than those associated with ICWs, and the permeability increase was not influenced by inhibition of PKC, CaMKII or actomyosin contraction. We conclude that ICWs significantly increase endothelial permeability and therefore, the connexins that underlie wave propagation form an interesting target to limit BBB alterations. This article is part of a Special Issue entitled Electrical Synapses.

Hyperglycemia and endothelial dysfunction in atherosclerosis: lessons from type 1 diabetes

A clear relationship between diabetes and cardiovascular disease has been established for decades. Despite this, the mechanisms by which diabetes contributes to plaque formation remain in question. Some of this confusion derives from studies in type 2 diabetics where multiple components of metabolic syndrome show proatherosclerotic effects independent of underlying diabetes. However, the hyperglycemia that defines the diabetic condition independently affects atherogenesis in cell culture systems, animal models, and human patients. Endothelial cell biology plays a central role in atherosclerotic plaque formation regulating vessel permeability, inflammation, and thrombosis. The current paper highlights the mechanisms by which hyperglycemia affects endothelial cell biology to promote plaque formation.

Leukocyte rolling and adhesion both contribute to regulation of microvascular permeability to albumin via ligation of ICAM-1

Activated neutrophils interacting with the vessel wall can alter vascular permeability to macromolecules such as albumin via release of various secretion products that induce changes in the endothelial monolayer. In the current work we used cremaster microvessels of anesthetized mice to show that, in addition to this paracrine mechanism, leukocyte ligation of endothelial ICAM-1 directly activates endothelial cell (EC) signaling, altering EC permeability to albumin [i.e., solute permeability (P(s))]. We show that antibody cross-linking of surface ICAM-1 in intact microvessels is sufficient to increase P(s) even in the absence of interacting leukocytes. Unstimulated arterioles do not support leukocyte-EC interactions, but despite this, antibody ligation of ICAM-1 in these vessels induced a twofold increase in P(s). Similarly, in venules that were depleted of interacting neutrophils, P(s) was decreased to below resting levels and was restored by ligation of ICAM-1. Use of function-blocking antibodies to separately block leukocyte rolling or adhesion under unstimulated or TNF-α-activated conditions established that both rolling and adhered leukocytes contribute to P(s) regulation in situ. Both rolling and adhesion activated EC-dependent signaling mechanisms that increased P(s). ICAM-1 ligation with primary antibody alone or primary followed by secondary antibodies showed that regulation of P(s) is directly dependent on the degree of ICAM-1 clustering. Under physiological versus inflamed conditions, respectively, this ICAM-1 clustering-dependent regulation of P(s) switches from PKC dependent and Src independent to Src dependent and PKC independent. This study thus identifies a new mechanism by which antiadhesion treatment may constitute a potential therapy for tissue edema.

Interplay between FAK, PKCδ, and p190RhoGAP in the regulation of endothelial barrier function

Disruption of either intercellular or extracellular junctions involved in maintaining endothelial barrier function can result in increased endothelial permeability. Increased endothelial permeability, in turn, allows for the unregulated movement of fluid and solutes out of the vasculature and into the surrounding connective tissue, contributing to a number of disease states, including stroke and pulmonary edema (Ermert et al., 1995; Lee and Slutsky, 2010; van Hinsbergh, 1997; Waller et al., 1996; Warboys et al., 2010). Thus, a better understanding of the molecular mechanisms by which endothelial cell junction integrity is controlled is necessary for development of therapies aimed at treating such conditions. In this review, we will discuss the functions of three signaling molecules known to be involved in regulation of endothelial permeability: focal adhesion kinase (FAK), protein kinase C delta (PKCδ), and p190RhoGAP (p190). We will discuss the independent functions of each protein, as well as the interplay that exists between them and the effects of such interactions on endothelial function.

Differential expression of protein kinase C isoforms in coronary arteries of diabetic mice lacking the G-protein Gα11

Background

Diabetes mellitus counts as a major risk factor for developing atherosclerosis. The activation of protein kinase C (PKC) is commonly known to take a pivotal part in the pathogenesis of atherosclerosis, though the influence of specific PKC isozymes remains unclear. There is evidence from large clinical trials suggesting excessive neurohumoral stimulation, amongst other pathways leading to PKC activation, as a central mechanism in the pathogenesis of diabetic heart disease. The present study was therefore designed to determine the role of G_q-protein signalling via Gα₁₁ in diabetes for the expression of PKC isozymes in the coronary vessels.

Methods

The role of Gα₁₁ in diabetes was examined in knockout mice with global deletion of Gα₁₁ compared to wildtype controls. An experimental type 1-diabetes was induced in both groups by injection of streptozotocin. Expression and localization of the PKC isozymes α, βII, δ, ε, and ζ was examined by quantitative immunohistochemistry.

Results

8 weeks after induction of diabetes a diminished expression of PKC ε was observed in wildtype animals. This alteration was not seen in Gα₁₁ knockout animals, however, these mice showed a diminished expression of PKCζ. Direct comparison of wildtype and knockout control animals revealed a diminished expression of PKC δ and ε in Gα₁₁ knockout animals.

Conclusion

The present study shows that expression of the nPKCs δ and ε in coronary vessels is under control of the g-protein Gα₁₁. The reduced expression of PKC ζ that we observed in coronary arteries from Gα₁₁-knockout mice compared to wildtype controls upon induction of diabetes could reduce apoptosis and promote plaque stability. These findings suggest a mechanism that may in part underlie the therapeutic benefit of RAS inhibition on cardiovascular endpoints in diabetic patients.

The NO cascade, eNOS location, and microvascular permeability

The nitric oxide (NO) cascade and endothelial NO synthase (eNOS) are best known for their role in endothelium-mediated relaxation of vascular smooth muscle. Activation of eNOS by certain inflammatory stimuli and enhanced NO release have also been shown to promote increased microvascular permeability. However, it is not entirely clear why activation of eNOS by certain vasodilatory agents, like acetylcholine, does not affect microvascular permeability, whereas activation of eNOS by other inflammatory agents that increase permeability, like platelet-activating factor, does not cause vasodilation. In this review, we discuss the evidence demonstrating the role of eNOS in the elevation of microvascular permeability. We also examine the relative importance of eNOS phosphorylation and localization in its function to promote elevated microvascular permeability as well as emerging topics with regard to eNOS and microvascular permeability regulation.

Translocation of protein kinase C isoforms is involved in propofol-induced endothelial nitric oxide synthase activation

BACKGROUND

Previous studies have indicated that protein kinase C (PKC) may enhance endothelial nitric oxide synthase (eNOS) activation, although the detailed mechanism(s) remains unclear. In this study, we investigated the roles of PKC isoforms in regulating propofol-induced eNOS activation in human umbilical vein endothelial cells (HUVECs).

METHODS

We applied western blot (WB) analysis to investigate the effects of propofol on Ser(1177) phosphorylation-dependent eNOS activation in HUVECs. Nitrite (NO(2)(-)) accumulation was measured using the Griess assay. The phosphatidylinositol 3-kinase/Akt (PI3K/Akt) pathway was examined by WB assay. Propofol-induced translocation of individual PKC isoforms in subcellular fractions in HUVECs was analysed using WB assay.

RESULTS

In HUVECs, protocol treatment (1-100 microM) for 10 min induced a concentration-dependent increase in phosphorylation of eNOS at Ser(1177). The NO production was also increased accordingly. PKC inhibitors, bisindolylmaleimide I (0.1-1 microM), and staurosporine (20 and 100 nM), effectively blocked propofol-induced eNOS activation and NO production. Further analyses in fractionated endothelial lysate showed that short-term propofol treatment (50 microM) led to translocation of PKC-alpha, PKC-delta, PKC-zeta, PKC-eta, and PKC-epsilon from cytosolic to membrane fractions, which could also be inhibited by both PKC inhibitors. These data revealed that the differential redistribution of these isozymes is indispensable for propofol-induced eNOS activation. In addition, Akt was not phosphorylated in response to propofol at Ser(473) or Thr(308).

CONCLUSIONS

Propofol induces the Ser(1177) phosphorylation-dependent eNOS activation through the drug-stimulated translocation of PKC isoforms to distinct intracellular sites in HUVECs, which is independent of PI3K/Akt-independent pathway.

Role of PKCbetaII and PKCdelta in blood-brain barrier permeability during aglycemic hypoxia

Blood-brain barrier (BBB) dysfunction contributes to the pathophysiology of cerebrovascular diseases such as stroke. In the present study, we investigated the role of PKC isoforms in aglycemic hypoxia-induced hyperpermeability using an in vitro model of the BBB consisting of mouse bEnd.3 cells. PKCbetaII and PKCdelta isoforms were activated during aglycemic hypoxia. CGP53353, a specific PKCbetaII inhibitor, significantly attenuated aglycemic hypoxia-induced BBB hyperpermeability and disruption of occludin and zonula occludens-1 (ZO-1), indicating a deleterious role of PKCbetaII in the regulation of BBB permeability during aglycemic hypoxia. Conversely, rottlerin, a specific PKCdelta inhibitor, exacerbated BBB hyperpermeability and tight junction (TJ) disruption during aglycemic hypoxia, indicating a protective role of PKCdelta against aglycemic hypoxia-induced BBB hyperpermeability. Furthermore, disruption of TJ proteins during aglycemic hypoxia was attenuated by PKCbetaII DN and PKCdelta WT overexpression, and aggravated by PKCbetaII WT and PKCdelta DN overexpression. These results suggest that PKCbetaII and PKCdelta counter-regulate BBB permeability during aglycemic hypoxia.

Leukocyte-endothelial cell interactions are linked to vascular permeability via ICAM-1-mediated signaling

Two key characteristics of the inflammatory response are the recruitment of leukocytes to inflamed tissue as well as changes in vessel permeability. We explored the relationship between these two processes using intravital confocal microscopy in cremasters of anesthetized (65 mg/kg Nembutal ip) mice. We provide direct evidence that intercellular adhesion molecule-1 (ICAM-1) links leukocyte-endothelial cell interactions and changes in solute permeability (Ps). Importantly, we show that arterioles, not just venules, respond to proinflammatory stimuli, thus contributing to microvascular exchange. We identified two independent, ICAM-1-mediated pathways regulating Ps. Under control conditions in wild-type (WT) mice, there is a constitutive PKC-dependent pathway (Ps = 1.0 +/- 0.10 and 2.2 +/- 0.46 x 10(-6) cm/s in arterioles and venules, respectively), which was significantly reduced in ICAM-1 knockout (KO) mice (Ps = 0.54 +/- 0.07 and 0.77 +/- 0.11 x 10(-6) cm/s). The PKC inhibitor bisindolylmaleimid l (1 micromol/l in 0.01% DMSO) decreased P(s) in WT mice to levels similar to those in ICAM-1 KO mice. Likewise, a PKC activator (phorbol-12-myristate-acetate; 1 micromol/l in 0.01% DMSO) successfully restored Ps in ICAM-1 KO vessels to be not different from that of the WT controls. On the other hand, during TNF-alpha-induced inflammation, Ps in WT mice was significantly increased (2-fold in venules and 2.5-fold in arterioles) in a Src-dependent and PKC-independent manner. The blockade of Src (PP2; 2 micromol/l in 0.01% DMSO) but not PKC significantly reduced the TNF-alpha-dependent increase in Ps. We conclude that ICAM-1 plays an essential role in the regulation of Ps in microvessels and that there are two separate (constitutive and inducible) signaling pathways that regulate permeability under normal and inflamed conditions.