Inhibition of phospholipase C reduces the capacitation of cryopreserved ovine sperm

This study aimed to evaluate the effect of phospholipase C (PLC) on the capacitation of cryopreserved ovine semen. Sixteen semen samples were cryopreserved with diluent added by 0, 10, or 20 μM of U73122, a PLC inhibitor. The sperm kinetics of the thawed samples were evaluated using the "Computer-assisted Sperm Analysis" system, and the integrity of the plasma and mitochondrial membranes was evaluated using fluorescent probes. Additionally, sperm capacitation and the acrosome reaction with chlortetracycline hydrochloride were evaluated before and after capacitation induction. The results were analysed using analysis of variance and Tukey's test with a 95% probability. Concentrations of 10 or 20 μM of U73122 did not affect the kinetics or number of sperm with intact plasma and mitochondrial membranes. However, after thawing, 10 and 20 μM of the inhibitor reduced the percentage of capacitated and acrosome-reacted sperm. After induction of capacitation, there was a reduction in the number of non-capacitated sperm in all treatment groups, suggesting a reversible effect of U73122. In conclusion, U73122 at concentrations of 10 or 20 μM prevents premature capacitation and acrosome reaction induced by the freezing procedure, without affecting the kinetics and integrity of the sperm membranes.

Factors Affecting the Release of Haemoglobin and Enzymes from Human Erythrocytes

The efflux of lactate dehydrogenase and haemoglobin from human erythrocytes during prolonged incubation at 37° was significantly reduced by ATP, ADP, AMP, UTP, creatine phosphate, or phosphoenolpyruvate and to a lesser extent by fructose, glucose 6-phosphate or fructose 6-phosphate, but not by glucose. Iodoacetate, however, markedly increased the loss of haemoglobin and slightly increased that of lactate dehydrogenase.

Phospholipase C greatly accelerated the relase of haemoglobin, lactate dehydrogenase, pyruvate kinase, hexokinase, glucose 6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase from human erythrocytes, but this effect was also reduced in the presence of ATP or ADP. The loss of lactate dehydrogenase, malate dehydrogenase, and pyruvate kinase from the cells treated with phospholipase C increased as their ATP content fell. In a series of experiments in which the action of phospholipase C was stopped by the subsequent addition of trypsin, ATP and ADP (1 mmol/l) significantly reduced the efflux of haemoglobin, but AMP had no such effect.

The results are consistent with the conclusion from our previous work that enzyme leakage is related to diminution in the energy content of the cells. The protective action of AMP on cells not treated with phospholipase C, however, differs from earlier findings with rat lymphocytes and it is suggested that in red cells it might be converted into ATP or that it has a direct effect on the permeability of the cell membrane.

LETAL, A Tumor-Associated NKG2D Immunoreceptor Ligand, Induces Activation and Expansion of Effector Immune Cells

NKG2D serves as one of the most potent activating receptors for effector lymphocytes. in peripheral tissues. Here we report the characterization of Letal, the first human trans-membrane NKG2D ligand lacking an immunoglobulin-like alpha-3 ectodomain. Letal is constitutively expressed by a variety of normal tissues, and is upregulated in tumor cells of different origins. Unlike other NKG2D ligands, Letal mRNA expression progressively decreased after treatment of tumor cells with retinoic acid. Simultaneous T-cell receptor activation and engagement of Letal stimulated proliferation of CD8(+) cells and dramatically increased IL-2 and IFNgamma secretion. In addition, Letal induced the killing of cancer cells by CD8(+) and NK cells. These results suggest that Letal delivers activating signals to NK cells and promotes tumor immune surveillance by inducing the expansion of anti-tumor cytotoxic lymphocytes.

Clostridium perfringens phospholipase C induced ROS production and cytotoxicity require PKC, MEK1 and NFκB activation

Clostridium perfringens phospholipase C (CpPLC), also called α-toxin, is the most toxic extracellular enzyme produced by this bacteria and is essential for virulence in gas gangrene. At lytic concentrations, CpPLC causes membrane disruption, whereas at sublytic concentrations this toxin causes oxidative stress and activates the MEK/ERK pathway, which contributes to its cytotoxic and myotoxic effects. In the present work, the role of PKC, ERK 1/2 and NFκB signalling pathways in ROS generation induced by CpPLC and their contribution to CpPLC-induced cytotoxicity was evaluated. The results demonstrate that CpPLC induces ROS production through PKC, MEK/ERK and NFκB pathways, the latter being activated by the MEK/ERK signalling cascade. Inhibition of either of these signalling pathways prevents CpPLC's cytotoxic effect. In addition, it was demonstrated that NFκB inhibition leads to a significant reduction in the myotoxicity induced by intramuscular injection of CpPLC in mice. Understanding the role of these signalling pathways could lead towards developing rational therapeutic strategies aimed to reduce cell death during a clostridialmyonecrosis.

[New insight from basic research of Clostridium perfringens alpha-toxin]

Clostridium perfringens causes gas gangrene with inflammatory myopathies and infrequently septicemia associated with massive intravascular hemolysis. The microorganism is known to produce a variety of toxins and enzymes that are responsible for severe myonecrotic lesions. Notably, alpha-toxin, which possesses hemolytic, necrotic and lethal activities, and phospholipase C and sphingomyelinase activities, is an important agent for the diseases. The cytokine storm induced by alpha-toxin, mainly the release of TNF-alpha, plays an important role in the death and massive hemolysis. The toxin-induced release of TNF-alpha from neutrophils and macrophages is dependent on the activation of ERK1/2 signal transduction via TrkA receptor. In addition, 14- and 15-membered macrolides specifically block the toxin-induced events through the activation of neutrophils and macrophages.

Induction of neurite-outgrowth in PC12 cells by alpha-toxin from Clostridium perfringens

Alpha-toxin-induced phosphorylation of PDK1 via the tyrosine kinase A (TrkA) receptor signaling pathway plays an important role in the activation of rabbit neutrophils. The relation between the toxin and TrkA, however, remains poorly understood. Here, we show that the toxin-induced phosphorylation of TrkA is closely related to the induction of neurite-outgrowth in PC12 cells. The toxin induced neurite-outgrowth and phosphorylation of TrkA in the cells in a dose-dependent manner. K252a, a TrkA inhibitor, and shRNA for TrkA inhibited the toxin-induced neurite-outgrowth, and phosphorylation of TrkA and ERK1/2. PD98059, an inhibitor of the ERK1/2 cascade, inhibited phosphorylation of ERK1/2 and the neurite-outgrowth induced by alpha-toxin. The wild-type toxin induced the formation of diacylglycerol, and neurite-outgrowth, but H148G, a variant toxin which binds to cell membranes and has lost the enzymatic activity did not. We demonstrated that the phosphorylation of TrkA through the phospholipid metabolism induced by the toxin synergistically play a key role in neurite-outgrowth.

Effect of phospholipase C induced hydrolysis of phospholipids on membrane-bound and water-soluble LH/hCG receptors in porcine corpora lutea

The role of phospholipids in the function of LH/hCG receptors was studied in two receptor preparations: the membrane fraction of porcine corpora lutea (CL) and the water-soluble receptor in follicular fluid (LFF) which was characterized. Digestion of CL membranes with phospholipase C (PL-C) abolished, in a dose responsive manner, specific binding of [125I]hCG and decreased phospholipid concentrations in the membranes. This loss of LH/hCG receptors was prevented by o-phenanthroline, an inhibitor of PL-C. A similar effect on membrane-bound receptors was observed when lipids were extracted with ethanol-diethylether. On the other hand, treatment of water-soluble receptors with PL-C or delipidation of LFF with Amberlit IRA 400 had no effect on [125I]hCG specific binding. These data suggest that phospholipids play an important role in the accessibility of membrane-bound receptors but are not involved in direct interaction of gonadotropin with binding sites.

Factor VII-phospholipid complex in male survivors of acute myocardial infarction

The presence of an activated form of coagulation factor VII--a factor VII-phospholipid complex--in male survivors of myocardial infarction is described. The level of this complex did not correlate with age or level of conventional risk factor score, but showed a highly significant positive correlation with serum triglycerides in all the subgroups as well as in the whole study population (r = 0.88, p less than 0.0001). Measurement of this form of activated factor VII may constitute a simple and promising method for additional screening of men at risk for cardiovascular disease.

Signalling mitogenesis in 3T3 cells: role of Ca2+-sensitive, phospholipid-dependent protein kinase

Understanding the molecular mechanisms that control cell proliferation requires the identification of the early signals important for initiating a mitogenic response. In this context, the activation of Ca2+-sensitive, phospholipid-dependent protein kinase (protein kinase C), which is stimulated by diacylglycerols and serves as a major phorbol ester receptor, may play an important part in signalling mitogenesis. This conclusion is based on two main lines of evidence. Firstly, activation of protein kinase C in intact quiescent fibroblasts is one of the earliest events elicited by a variety of growth-promoting agents including serum, platelet-derived growth factor (PDGF), vasopressin and bombesin, as judged by the increase in the phosphorylation of a cellular protein characterized by an Mr of 80 000 and a pI of 5. Secondly, the synthetic diacylglycerol, 1-oleoyl-2-acetylglycerol, which directly competes with [3H]phorbol dibutyrate for binding to specific receptors in intact 3T3 cells and rapidly stimulates protein kinase C in these cells, is a potent mitogen for Swiss 3T3 cells, acting synergistically with other growth factors. We propose that activation of protein kinase C may be one of the early signals that mediate the mitogenic effects of a variety of growth factors and peptide hormones in quiescent fibroblastic cells.

RhoA/Rho kinase-mediated Ca2+ sensitization in the contraction of human prostate

AIMS

The contractile mechanisms of prostatic smooth muscle have been extensively investigated at the receptor level. However, the intracellular mechanisms have not yet been fully elucidated, especially in human tissue. In the present study, we examined the functional role of RhoA/Rho kinase (ROCK), one of the major intracellular molecules involved in smooth muscle contraction, in the contraction of the human prostate.

METHODS

Ring preparations made of cultured human prostatic stromal cells (CHPSCs) or fresh human prostatic tissue was used for an isometric tension study. Gene transfer using baculovirus vector and alpha-toxin permeabilized preparations were also used.

RESULTS

RhoA, ROCK I and ROCK II proteins were all expressed in CHPSCs and fresh human prostatic tissue. In CHPSCs ring preparations, the contraction induced by endothelin (ET)-1 was enhanced by over-expression of RhoA and inhibited by ROCK inhibitor. In alpha-toxin permeabilized preparations, ET-1 or GTP-gammaS induced an additional contraction at a constant [Ca2+]i, that was inhibited by ROCK inhibitor. In fresh human prostatic tissue, norepinephrine (NE)-induced contraction was inhibited by ROCK inhibitor at a constant [Ca2+]i in alpha-toxin permeabilized preparations.

CONCLUSIONS

These results suggested that RhoA/ROCK-mediated Ca2+ sensitization is likely involved in the contraction of the human prostate. The antagonisms of this pathway may thus be useful as an alternative target in the treatment of benign prostatic hyperplasia (BPH).

Nod1 mediates cytoplasmic sensing of combinations of extracellular bacteria

During mucosal colonization, epithelial cells are concurrently exposed to numerous microbial species. Epithelial cytokine production is an early component of innate immunity and contributes to mucosal defence. We have previously demonstrated a synergistic response of respiratory epithelial cells to costimulation by two human pathogens, Streptococcus pneumoniae and Haemophilus influenzae. Here we define a molecular mechanism for the synergistic activation of epithelial signalling during polymicrobial colonization. H. influenzae peptidoglycan synergizes with the pore-forming toxin pneumolysin from S. pneumoniae. Radiolabelled peptidoglycan enters epithelial cells more efficiently in the presence of pneumolysin, consistent with peptidoglycan gaining access to the cytoplasm via toxin pores. Other pore-forming toxins (including anthrolysin O from Bacillus anthracis and Staphylococcus aureus alpha-toxin) can substitute for pneumolysin in the generation of synergistic responses. Consistent with a requirement for pore formation, S. pneumoniae expressing pneumolysin but not an isogenic mutant expressing a non-pore-forming toxoid prime epithelial responses. Nod1, a host cytoplasmic peptidoglycan-recognition molecule, is crucial to the epithelial response. Taken together, these findings demonstrate a role for cytosolic recognition of peptidoglycan in the setting of polymicrobial epithelial stimulation. We conclude that combinations of extracellular organisms can activate innate immune pathways previously considered to be reserved for the detection of intracellular microorganisms.

Adenosine A1 receptor-mediated inhibition of in vitro prolactin secretion from the rat anterior pituitary

In previous studies, we demonstrated biphasic purinergic effects on prolactin (PRL) secretion stimulated by an adenosine A2 agonist. In the present study, we investigated the role of the activation of adenosine A1 receptors by (R)-N6-(2-phenylisopropyl)adenosine (R-PIA) at the pituitary level in in vitro PRL secretion. Hemipituitaries (one per cuvette in five replicates) from adult male rats were incubated. Administration of R-PIA (0.001, 0.01, 0.1, 1, and 10 microM) induced a reduction of PRL secretion into the medium in a U-shaped dose-response curve. The maximal reduction was obtained with 0.1 microM R-PIA (mean +/- SEM, 36.01 +/- 5.53 ng/mg tissue weight (t.w.)) treatment compared to control (264.56 +/- 15.46 ng/mg t.w.). R-PIA inhibition (0.01 microM = 141.97 +/- 15.79 vs control = 244.77 +/- 13.79 ng/mg t.w.) of PRL release was blocked by 1 microM cyclopentyltheophylline, a specific A1 receptor antagonist (1 microM = 212.360 +/- 26.560 ng/mg t.w.), whereas cyclopentyltheophylline alone (0.01, 0.1, 1 microM) had no effect. R-PIA (0.001, 0.01, 0.1, 1 microM) produced inhibition of PRL secretion stimulated by both phospholipase C (0.5 IU/mL; 977.44 +/- 76.17 ng/mg t.w.) and dibutyryl cAMP (1 mM; 415.93 +/- 37.66 ng/mg t.w.) with nadir established at the dose of 0.1 microM (225.55 +/- 71.42 and 201.9 +/- 19.08 ng/mg t.w., respectively). Similarly, R-PIA (0.01 microM) decreased (242.00 +/- 24.00 ng/mg t.w.) the PRL secretion stimulated by cholera toxin (0.5 mg/mL; 1050.00 +/- 70.00 ng/mg t.w.). In contrast, R-PIA had no effect (468.00 +/- 34.00 ng/mg t.w.) on PRL secretion stimulation by pertussis toxin (0.5 mg/mL; 430.00 +/- 26.00 ng/mg t.w.). These results suggest that inhibition of PRL secretion after A1 receptor activation by R-PIA is mediated by a Gi protein-dependent mechanism.

Dimethyl sulphoxide relaxes rabbit detrusor muscle by decreasing the Ca2+ sensitivity of the contractile apparatus

BACKGROUND AND PURPOSE

The intravesical administration of dimethyl sulphoxide (DMSO) is used to alleviate the symptoms of interstitial cystitis. We investigated the relaxant effect of DMSO and its underlying mechanism in the detrusor muscle.

EXPERIMENTAL APPROACH

The effects of DMSO on contraction, on Ca2+ sensitivity of myofilaments, and on myosin light chain (MLC) phosphorylation were investigated in both intact and alpha-toxin-permeabilized strips of rabbit detrusor muscle.

KEY RESULTS

In fura-PE3-loaded strips, DMSO (>1%) induced a significant relaxation during sustained contractions induced by 60 mM K+-depolarization or 10 microM carbachol, while having no effect on the [Ca2+](i) level. DMSO decreased the level of MLC phosphorylation during the contractions induced by 60 mM K+ and 10 microM carbachol. DMSO also inhibited both the contraction and MLC phosphorylation induced by calyculin-A in intact strips. In the alpha-toxin-permeabilized preparations, DMSO relaxed the Ca2+-induced contraction and also inhibited the tension development induced by a stepwise increment of Ca2+ concentrations. Such a relaxant effect of DMSO was enhanced in the presence of phosphate.

CONCLUSIONS AND IMPLICATIONS

DMSO relaxes rabbit detrusor muscle by decreasing the Ca2+ sensitivity of myofilaments. Inhibition of the kinase activities involved in myosin phosphorylation may play a major role in DMSO-induced Ca2+ desensitization. Inhibition of the cross-bridge cycling at the step of phosphate release may also contribute to the relaxant effect of DMSO. Such relaxant effects of DMSO could be linked to the therapeutic effect of DMSO in interstitial cystitis.

Sphingosine‐1‐phosphate and the immunosuppressant, FTY720‐phosphate, regulate detrusor muscle tone

Overactive bladder syndrome (OBS) results from disturbances of bladder function. Bladder smooth muscle (detrusor) exhibits spontaneous rhythmic activity (tone) independent of neurogenic control, which is enhanced in patients with OBS. We have now uncovered a prominent role for the bioactive sphingolipid metabolite, sphingosine-1-phosphate (S1P), in regulating rabbit detrusor smooth muscle tone and contraction. S1P-induced contraction of detrusor muscle was dependent on stretch and intracellular calcium. Although detrusor expresses the S1P receptors S1P1 and S1P2, only S1P2 appeared to be involved in S1P-induced contraction, since SEW2871 (S1P1 agonist) and dihydro-S1P (potent agonist for all S1P receptors except S1P2) were poor contractile agents. In agreement, the S1P2 antagonist JTE013 inhibited S1P-induced contraction. The fast, transient muscle contraction (phasic) mediated by S1P was dependent on phospholipase C (PLC) whereas the slower, sustained contraction (tonic) was not. Surprisingly, the immunosuppressant FTY720-phosphate, an agonist for all S1P receptors except S1P2, had distinct contractile properties and also induced slow, sustained contraction. Thus, FTY720-phosphate and/or S1P may regulate calcium channels in an S1P receptor-independent manner. Collectively, our results demonstrate that S1P may regulate detrusor smooth muscle tone and suggest that dysregulation of complex S1P signaling might contribute to OBS.

The influence of hyaluronan-CD44 interaction on topoisomerase II activity and etoposide cytotoxicity in head and neck cancer

OBJECTIVE

To investigate the downstream molecular targets of hyaluronan (HA)-CD44 and phospholipase C (PLC)-mediated calcium ion (Ca(2+)) signaling in head and neck squamous cell carcinoma (HNSCC). Hyaluronan is a ligand for the CD44 receptor, which interacts with multiple signaling pathways to influence cellular behavior. We recently determined that HA-CD44 interaction promotes PLC-mediated Ca(2+) signaling and cisplatin resistance in HNSCC.

DESIGN

Proliferation of HNSCC tumor cells and topoisomerase (Topo) II enzymatic activity, including DNA-cleavable complex formation and DNA decatenation, were analyzed in the presence or absence of HA, the Topo II poison etoposide (VP-16), and various inhibitors of PLC and Ca(2+)-calmodulin kinase II (CaMKII) signaling.

RESULTS

Treatment with HA promoted Topo II phosphorylation, suggesting that HA can modulate Topo II activity. Topoisomerase II-mediated DNA cleavable complex formation was increased by VP-16, and this increase was significantly enhanced by noncytotoxic doses of the PLC inhibitor U73122 and the CaMKII inhibitor KN-62, implicating PLC and CaMKII in Topo II regulation. However, the drug- and inhibitor-mediated increase in DNA cleavable complex formation was reduced with HA pretreatment. Inhibitors of PLC and CaMKII also enhanced VP-16 inhibition of Topo II-mediated DNA decatenation. Treatment with HA reduced VP-16 cytotoxic activity. On the other hand, U73122 and KN-62 enhanced VP-16 cytotoxic activity and reduced the ability of HA to promote VP-16 resistance.

CONCLUSION

Our results suggest that HA, PLC, and CaMKII are upstream regulators of Topo II-mediated DNA metabolism in HNSCC and that this signaling pathway could be a promising target for the development of novel therapies against HNSCC.

Sulfatide-tenascin interaction mediates binding to the extracellular matrix and endocytic uptake of liposomes in glioma cells

Tenascin-C is an extracellular matrix glycoprotein, whose expression is highly restricted in normal adult tissues, but markedly up-regulated in a range of tumors, and therefore serves as a potential receptor for targeted anticancer drug or gene delivery. We describe here a liposomal carrier system in which the targeting ligand is sulfatide. Experiments with tenascin-C-expressing glioma cells demonstrated that binding of liposomes to the extracellular matrix relied essentially on the sulfatide-tenascin-C interaction. Following binding to the extracellular matrix, the sulfatide-containing liposomes were internalized via both caveolae/lipid raft- and clathrin-dependent pathways, which would ensure direct cytoplasmic release of the cargoes carried in the liposomes. Such natural lipid-guided intracellular delivery targeting at the extracellular matrix glycoproteins of tumor cells thus opens a new direction for development of more effective anticancer chemotherapeutics in future.

siRNA knock down of casein kinase 2 increases force and cross-bridge cycling rates in vascular smooth muscle

Contraction of smooth muscle involves myosin light chain (MLC) kinase catalyzed phosphorylation of the regulatory MLC, activation of myosin, and the development of force. However, this cannot account for all aspects of a smooth muscle contraction, suggesting that other regulatory mechanisms exist. One potentially important technique to study alternative sites of contractile regulation is the use of small interfering RNA (siRNA). The goal of this study was to determine whether siRNA technology can decrease the levels of a specific protein and allow for the determination of how that protein affects contractile regulation. To achieve this goal, we tested the hypothesis that casein kinase 2 (CK2) is part of the complex regulatory scheme present in vascular smooth muscle. Using intact strips of swine carotid artery, we determined that siRNA against CK2 produced a tissue that resulted in a ∼60% knockdown after 4 days in organ culture. Intact strips of vascular tissue depleted of CK2 produced greater levels of force and exhibited an increased sensitivity to all stimuli tested. This was accompanied by an increase in cross-bridge cycling rates but not by a change in MLC phosphorylation levels. α-Toxin-permeabilized vascular tissue depleted of CK2 also showed an increased sensitivity to calcium compared with control tissues. Our results demonstrate that siRNA is a viable technique with which to study regulatory pathways in intact smooth muscle tissue. Our results also demonstrate that CK2 plays an important role in the mechanism(s) responsible for the development of force and cross-bridge cycling by a MLC phosphorylation-independent pathway.

Perfluorocarbon suppresses lipopolysaccharide- and alpha-toxin-induced interleukin-8 release from alveolar epithelial cells

BACKGROUND/AIMS

Human pulmonary alveolar epithelial (A549) cells release interleukin-8 (IL-8) on stimulation by lipopolysaccharide (LPS) and alpha-toxin. We hypothesised that the perfluorocarbons (PFCs), perflubron and FC-84, would block stimulation of A549 cells by these toxins.

METHODS

The levels of IL-8 production in A549 cells were measured following exposure to toxins for 24 h with or without PFC. The amount of IL-8 released from A549 cells was measured by enzyme-linked immunosorbent assay, and the level of IL-8 mRNA was measured by real-time RT-PCR.

RESULTS

When stimulated with LPS or alpha-toxin, IL-8 release from A549 cells increased. There were no significant differences in level of IL-8 release between cells pre-incubated for 24 h with or without PFC after toxin stimulation for 24 h. When PFC was administered along with LPS stimulation, the level of IL-8 release was decreased (LPS control, 1,398 +/- 110 pg/well; FC-84, 686 +/- 50 pg/well; perflubron, 749 +/- 137 pg/well; p < 0.05). Levels of IL-8 mRNA expression were significantly higher with than without LPS, and those with LPS and perflubron were significantly lower than those with LPS alone.

CONCLUSIONS

The results show that PFCs block stimulation of A549 cells by LPS or alpha-toxin. PFC may be useful clinically in treatment of pulmonary inflammation in the alveolar space.

Prostaglandin F2alpha, but not latanoprost, increases the Ca2+ sensitivity of the pig iris sphincter muscle

PURPOSE

To determine the mechanisms underlying prostaglandin (PG) F(2)alpha-(,) carbachol (CCh)-, or latanoprost (a PGF(2)alpha analogue)-induced contraction of the pig iris sphincter muscle.

METHODS

Effects of these agents on myofilament Ca(2+) sensitivity were evaluated and compared with the use of receptor-coupled permeabilized preparations by alpha-toxin. The effects of PGF(2)alpha and CCh on the phosphorylation of myosin light chain (MLC) were also analyzed.

RESULTS

In the intact strips, all three of these agents induced contractions. In permeabilized strips, PGF(2)alpha and CCh, but not latanoprost, caused an additional tension development at a fixed intracellular Ca(2+) concentration ([Ca(2+)](i)) and also shifted the [Ca(2+)](i)-tension curve to the left, thus indicating that PGF(2)alpha and CCh, but not latanoprost, induced increases in Ca(2+) sensitivity (Ca(2+) sensitization). This Ca(2+) sensitization could have been inhibited by Y27632, a rho kinase inhibitor, but not by GF109203X, a protein kinase C (PKC) inhibitor or by PD98059, a mitogen-activated protein (MAP) kinase inhibitor. PGF(2)alpha increased the level of MLC phosphorylation at a constant [Ca(2+)](i).

CONCLUSIONS

PGF(2)alpha, but not latanoprost, induced Ca(2+) sensitization of the pig iris sphincter muscle in an MLC phosphorylation-dependent manner through the rho-rho kinase pathway. The effect of latanoprost on the Ca(2+) sensitization mechanism was different from that of PGF(2)alpha and was thought to play a beneficial role in glaucoma treatment.

Biosensor incorporating cell barrier architectures for detecting Staphylococcus aureus alpha toxin

Alpha toxin is a common virulent factor of Staphylococcus aureus and is believed to play crucial roles in pathogenicity induced by S. aureus. Alpha toxin is also known to induce permeability to endothelial cell monolayers in vitro due to the formation of interendothelial gaps. The present study is directed towards measuring alpha toxin using a whole-cell-based biosensor. The biosensor, consisting of a confluent monolayer of human umbilical vein endothelial cells (HUVECs) on a potassium ion-selective electrode, takes advantage of cell permeability dysfunction to detect the presence of small quantities of alpha toxin. When a confluent monolayer of cells was formed on the membrane surface, the response of the electrode toward the marker ion, potassium, was inhibited. Upon exposing this sensor to varying concentrations of alpha toxin for 20 min, an increase in sensor response to potassium was observed. The response thus obtained was indirectly related to the concentration of alpha toxin. The detection limit of this sensor for alpha toxin was found to be 0.1 ng/ml. Cell monolayers were stained with silver nitrate to quantify the formation of intercellular gaps as well as to study the effect of this toxin on HUVECs morphology. A strong positive correlation was observed between the response obtained from the biosensor and the area of the intercellular gaps. Silver staining also revealed the tendency of cells to round up upon being exposed to alpha toxin.

Inositol 1,4,5-trisphosphate supports the arrhythmogenic action of endothelin-1 on ventricular cardiac myocytes

Although ventricular cardiomyocytes express inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] receptors, it is unclear how these Ca2+ channels contribute to the effects of Gq-coupled agonists. Endothelin-1 augmented the amplitude of pacing-evoked Ca2+ signals (positive inotropy), and caused an increasing frequency of spontaneous diastolic Ca2+-release transients. Both effects of endothelin-1 were blocked by an antagonist of phospholipase C, suggesting that Ins(1,4,5)P3 and/or diacylglycerol production was necessary. The endothelin-1-mediated spontaneous Ca2+ transients were abolished by application of 2-aminoethoxydiphenyl borate (2-APB), an antagonist of Ins(1,4,5)P3 receptors. Incubation of electrically-paced ventricular myocytes with a membrane-permeant Ins(1,4,5)P3 ester provoked the occurrence of spontaneous diastolic Ca2+ transients with the same characteristics and sensitivity to 2-APB as the events stimulated by endothelin-1. In addition to evoking spontaneous Ca2+ transients, stimulation of ventricular myocytes with the Ins(1,4,5)P3 ester caused a positive inotropic effect. The effects of endothelin-1 were compared with two other stimuli, isoproterenol and digoxin, which are known to induce inotropy and spontaneous Ca2+ transients by overloading intracellular Ca2+ stores. The events evoked by isoproterenol and digoxin were dissimilar from those triggered by endothelin-1 in several ways. We propose that Ins(1,4,5)P3 receptors support the development of both inotropy and spontaneous pro-arrhythmic Ca2+ signals in ventricular myocytes stimulated with a Gq-coupled agonist.

Clostridium perfringens alpha toxin affects electrophysiological properties of isolated jejunal mucosa of laying hens

Bacteria that colonize the intestinal tract can invade epithelial cells or produce toxins that cause diarrhoeal diseases. Proliferation of Clostridium perfringens and production of alpha-toxin, a phospholipase C, is the major factor for necrotic enteritis in poultry. However, little is known about the functional importance of luminal alpha-toxin during intestinal infection. The purpose of this study was to investigate the effects of purified alpha toxin of Clostridium perfringens on the electrophysiology of the laying hen's stripped jejunum in Ussing chambers. The effects were investigated in Experiment 1 after toxin addition to the mucosal and serosal side of the tissue, and a second experiment was performed to study the effect of the toxin on sodium-dependent glucose transport. Mucosal exposure of jejunal tissue sheets to 100 units of alpha toxin/L did not elicit electrophysiologic changes. The addition of purified alpha toxin to the serosal side induced a biphasic increase in short-circuit current (ISC) after 15 and 100 min. The magnitude of the increase of ISC of both peaks was similar, but the second phase response lasted longer. The tissue conductivity tended (P = 0.07) to be lower after 2 h of toxin addition compared with basal value when no toxin was added. In the second experiment, adding D-glucose on the mucosal side of the jejunum increased (P < 0.05) the ISC from a baseline value of 42 +/- 28 microA/cm2 to a maximal value of 103 +/- 27 microA/cm2. Preincubation with alpha-toxin almost fully inhibited this stimulation of ISC by D-glucose. The conductance of the tissues was not affected by the toxin addition. These findings indicate that alpha toxin not only causes electrogenic secretion of anions, probably due to the stimulation of chloride secretion, but also diminishes electrogenic Na+/glucose cotransport from the mucosal to serosal side in the small intestine of poultry.

Calcium sensitivity of vasospastic basilar artery after experimental subarachnoid hemorrhage

Arteries that develop vasospasm after subarachnoid hemorrhage (SAH) may have altered contractility and compliance. Whether these changes are due to alterations in the smooth muscle cells or the arterial wall extracellular matrix is unknown. This study elucidated the location of such changes and determined the calcium sensitivity of vasospastic arteries. Dogs were placed under general anesthesia and underwent creation of SAH using the double-hemorrhage model. Vasospasm was assessed by angiography performed before and 4, 7, or 21 days after SAH. Basilar arteries were excised from SAH or control dogs ( n = 8–52 arterial rings from 2–9 dogs per measurement) and studied under isometric tension in vitro before and after permeabilization of smooth muscle with α-toxin. Endothelium was removed from all arteries. Vasospastic arteries demonstrated significantly reduced contractility to KCl with a shift in the EC50toward reduced sensitivity to KCl 4 and 7 days after SAH ( P < 0.05, ANOVA). There was reduced compliance that persisted after permeabilization ( P < 0.05, ANOVA). Calcium sensitivity was decreased during vasospasm 4 and 7 days after SAH, as assessed in permeabilized arteries and in those contracted with BAY K 8644 in the presence of different concentrations of extracellular calcium ( P < 0.05, ANOVA). Depolymerization of actin with cytochalasin D abolished contractions to KCl but failed to alter arterial compliance. In conclusion, it is shown for the first time that calcium sensitivity is decreased during vasospasm after SAH in dogs, suggesting that other mechanisms are involved in maintaining the contraction. Reduced compliance seems to be due to an alteration in the arterial wall extracellullar matrix rather than the smooth muscle cells themselves because it cannot be alleviated by depolymerization of smooth muscle actin.

Urocortin-induced decrease in Ca2+ sensitivity of contraction in mouse tail arteries is attributable to cAMP-dependent dephosphorylation of MYPT1 and activation of myosin light chain phosphatase

Urocortin, a vasodilatory peptide related to corticotropin-releasing factor, may be an endogenous regulator of blood pressure. In vitro, rat tail arteries are relaxed by urocortin by a cAMP-mediated decrease in myofilament Ca2+ sensitivity through a still unclear mechanism. Here we show that contraction of intact mouse tail arteries induced with 42 mmol/L KCl or 0.5 micromol/L noradrenaline was associated with a approximately 2-fold increase in the phosphorylation of the regulatory subunit of myosin phosphatase (SMPP-1M), MYPT1, at Thr696, which was reversed in arteries relaxed with urocortin. Submaximally (pCa 6.1) contracted mouse tail arteries permeabilized with alpha-toxin were relaxed with urocortin by 39+/-3% at constant [Ca2+], which was associated with a decrease in myosin light chain (MLC20Ser19), MYPT1Thr696, and MYPT1Thr850 phosphorylation by 60%, 28%, and 52%, respectively. The Rho-associated kinase (ROK) inhibitor Y-27632 decreased MYPT1 phosphorylation by a similar extent. Inhibition of PP-2A with 3 nmol/L okadaic acid had no effect on MYPT1 phosphorylation, whereas inhibition of PP-1 with 3 micromol/L okadaic acid prevented dephosphorylation. Urocortin increased the rate of dephosphorylation of MLC20Ser19 approximately 2.2-fold but had no effect on the rate of contraction under conditions of, respectively, inhibited kinase and phosphatase activities. The effect of urocortin on MLC20Ser19 and MYPT1 phosphorylation was blocked by Rp-8-CPT-cAMPS and mimicked by Sp-5,6-DCl-cBIMPS. In summary, these results provide evidence that Ca(2+)-independent relaxation by urocortin can be attributed to a cAMP-mediated increased activity of SMPP-1M which at least in part is attributable to a decrease in the inhibitory phosphorylation of MYPT1.

Neurodegenerative illness in transgenic mice expressing a transmembrane form of the prion protein

Although PrP(Sc) is thought to be the infectious form of the prion protein, it may not be the form that is responsible for neuronal cell death in prion diseases. (Ctm)PrP is a transmembrane version of the prion protein that has been proposed to be a neurotoxic intermediate underlying prion-induced pathogenesis. To investigate this hypothesis, we have constructed transgenic mice that express L9R-3AV PrP, a mutant prion protein that is synthesized exclusively in the (Ctm)PrP form in transfected cells. These mice develop a fatal neurological illness characterized by ataxia and marked neuronal loss in the cerebellum and hippocampus. (Ctm)PrP in neurons cultured from transgenic mice is localized to the Golgi apparatus, rather than to the endoplasmic reticulum as in transfected cell lines. Surprisingly, development of the neurodegenerative phenotype is strongly dependent on coexpression of endogenous, wild-type PrP. Our results provide new insights into the cell biology of (Ctm)PrP, the mechanism by which it induces neurodegeneration, and possible cellular activities of PrP(C).

Sphingosylphosphorylcholine-induced vasoconstriction of pulmonary artery: activation of non-store-operated Ca2+ entry

OBJECTIVE

Sphingosylphosphorylcholine (SPC) is an important lipid mediator that has been implicated in vascular disease. As it has not been studied in the pulmonary circulation, we examined its mechanisms of action in rat small intrapulmonary arteries (IPA).

METHODS

IPA were mounted on a myograph for recording tension and intracellular Ca2+ concentration ([Ca2+]i). Ca2+ sensitisation was examined in alpha-toxin permeabilized IPA, and by Western blot analysis of MYPT1 phosphorylation.

RESULTS

SPC induced a slow but powerful vasoconstriction in IPA associated with an elevation in [Ca2+]i, with an EC50 for vasoconstriction of 12+/-2 microM. Removal of extracellular Ca2+ increased the EC50 to 76+/-33 microM (p<0.01) and abolished the rise in [Ca2+]i. Endothelial denudation or inhibition of NO synthase with L-NAME enhanced vasoconstriction. Treatment with pertussis toxin or the PLC inhibitor U731223 had no effect on SPC-induced vasoconstriction. The Rho kinase inhibitor Y27632 reduced SPC-induced vasoconstriction by approximately 70% and abolished both SPC-induced Ca2+ sensitisation in permeabilized IPA and the associated increase in MYPT1 phosphorylation; Ca2+ sensitisation was substantially inhibited by GDPbetaS. La3+ and 2-APB, at concentrations previously shown to block capacitative Ca2+ entry in IPA, suppressed SPC-induced vasoconstriction to the same extent as removal of extracellular Ca2+; residual tension was abolished by Y27632. Diltiazem was relatively ineffective. 2-APB also abolished the SPC-induced rise in [Ca2+]i. However, treatment with thapsigargin to empty intracellular stores had no effect on the elevation of [Ca2+]i induced by SPC.

CONCLUSION

We present evidence that SPC is a powerful vasoconstrictor of IPA and the novel finding that SPC-induced vasoconstriction in IPA is dependent on activation of a Ca2+ entry pathway with a similar sensitivity to La3+ and 2-APB as capacitative Ca2+ entry, although its activation is not dependent on emptying of PLC/IP3 or thapsigargin-sensitive intracellular stores.

Peptidases and gp63-like proteins in Herpetomonas megaseliae: possible involvement in the adhesion to the invertebrate host

The cell-associated and extracellular peptidases of Herpetomonas megaseliae grown in brain-heart infusion and in modified Roitman's complex media were analyzed by measuring peptidase activity on gelatin, casein and hemoglobin in zymograms. Casein was the best proteinaceous substrate for the peptidase detection on both growth conditions. However, no proteolytic activity was detected when hemoglobin was used. Our results showed that cellular cysteine peptidase (115-100, 40 and 35 kDa) and metallopeptidase (70 and 60 kDa) activities were detected on both media in casein and gelatin zymograms. Additionally, the use of casein in the gel revealed a distinct acidic metallopeptidase of 50 kDa when the parasite was cultured in the modified Roitman's complex medium. Irrespective of the culture medium composition, H. megaseliae released metallopeptidases exclusively in the extracellular environment. The presence of gp63-like molecules on the H. megaseliae surface was shown by flow cytometry using anti-gp63 antibody raised against recombinant gp63 from Leishmania mexicana. The pre-treatment of parasites with phospholipase C reduced the number of gp63-positive cells, suggesting that these molecules were glycosylphosphatidylinositol-anchored to the surface. Additionally, the supernatant obtained from phospholipase C-treated cells and probed with anti-cross-reacting determinant confirmed that at least a 52 kDa gp63-like molecule is glycosylphosphatidylinositol-anchored. Furthermore, we assessed a possible function for the gp63-like molecules in H. megaseliae on the interaction with explanted guts of its original host, Megaselia scalaris, and with an experimental model employing Aedes aegypti. Parasites pre-treated with either anti-gp63 antibody or phospholipase C showed a significant reduction in the adhesion to M. scalaris and A. aegypti guts. Similarly, the pre-treatment of the explanted guts with purified gp63 diminished the interaction process. Collectively, these results corroborate the ubiquitous existence of gp63 homologues in insect trypanosomatids and the potential adhesion of these molecules to invertebrate host tissues.

Sphingosine 1-phosphate is released from the cytosol of rat platelets in a carrier-mediated manner

Sphingosine 1-phosphate (S1P) is accumulated in platelets and released on stimulation by thrombin or Ca(2+). Thrombin-stimulated S1P release was inhibited by staurosporin, whereas Ca(2+)-stimulated release was not. When the platelet plasma membrane was permeabilized with streptolysin O (SLO), S1P leaked out with cytosol markers, whereas granular markers remained in the platelets. The SLO-induced S1P leakage required BSA, probably for solubilization of S1P in the medium. These results indicate that S1P is localized in the inner leaflet of the plasma membrane and that its release is a carrier-mediated process. We also used alpha-toxin (ATX), which makes smaller pores in the plasma membrane than SLO and depletes cytosolic ATP without BSA-dependent S1P leakage. The addition of ATP drove S1P release from ATX platelets. The ATP-driven S1P release from ATX platelets was greatly enhanced by thrombin. An ATP binding cassette transporter inhibitor, glyburide, prevents ATP- and thrombin-induced S1P release from platelets. Ca(2+) also stimulated S1P release from ATX platelets without ATP, whereas the Ca(2+)-induced release was not inhibited by glyburide. Our results indicate that two independent S1P release systems might exist in the platelet plasma membrane, an ATP-dependent system stimulated by thrombin and an ATP-independent system stimulated by Ca(2+).

Mechanisms of the prostaglandin F2alpha-induced rise in [Ca2+]i in rat intrapulmonary arteries

The mechanisms by which prostaglandin F(2alpha) (PGF(2alpha)) increases intracellular Ca2+ concentration [Ca2+]i in vascular smooth muscle remain unclear. We examined the role of store-, receptor- and voltage-operated Ca2+ influx pathways in rat intrapulmonary arteries (IPA) loaded with Fura PE-3. Low concentrations (0.01-1 microM) of PGF(2alpha) caused a transient followed by a plateau rise in [Ca2+]i. Both responses became maximal at 0.1 microM PGF(2alpha). At higher concentrations of PGF(2alpha), a further slower rise in [Ca2+]i was superimposed on the plateau. The [Ca2+]i response to 0.1 microM PGF(2alpha) was mimicked by the FP receptor agonist fluprostenol, whilst the effect of 10 microM PGF(2alpha) was mimicked by the TP receptor agonist U-46619. The plateau rise in [Ca2+]i in response to 0.1 microM PGF(2alpha) was insensitive to diltiazem, and was abolished in Ca2+-free physiological salt solution, and by pretreatment with La3+, 2-APB, thapsigargin or U-73122. The rises in [Ca2+]i in response to 10 microM PGF(2alpha) and 0.01 microM U-46619 were partially inhibited by diltiazem. The diltiazem-resistant components of both of these responses were inhibited by 2-APB and La3+ to an extent which was significantly less than that seen for the response to 0.1 microM PGF(2alpha), and were also much less sensitive to U-73122. The U-46619 response was also relatively insensitive to thapsigargin. When Ca2+ was replaced with Sr2+, the sustained increase in the Fura PE-3 signal to 0.1 microM PGF(2alpha) was abolished, whereas 10 microM PGF(2alpha) and 0.05 microM U-46619 still caused substantial increases. These results suggest that low concentrations of PGF(2alpha) act via FP receptors to cause IP3-dependent Ca2+ release and store operated Ca2+ entry (SOCE). U-46619 and 10-100 microM PGF(2alpha) cause a TP receptor-mediated Ca2+ influx involving both L-type Ca2+ channels and a receptor operated pathway, which differs from SOCE in its susceptibility to La3+, 2-APB and thapsigargin, does not require phospholipase C activation, and is Sr2+ permeable.

Fish somatostatin sst3 receptor: comparison of radioligand and GTPgammaS binding, adenylate cyclase and phospholipase C activities reveals different agonist-dependent pharmacological signatures

1 The fish somatostatin receptor 3 (fsst3) is one of the few somatostatin (SRIF) receptors cloned from a non-mammalian species so far. Here we extended our earlier characterization of this receptor by investigating the guanine nucleotide sensitivity of agonist radioligand binding at the fsst3 receptor recombinantly expressed in CCL39 (Chinese hamster lung fibroblast) cells. Further, we measured somatostatin (SRIF) and cortistatin (CST) analogues stimulated GTPgammaS binding, inhibition of forskolin-stimulated adenylate cyclase (FSAC) and stimulation of phospholipase C (PLC) activities. The present transductional data were then compared with previous radioligand binding and/or second messenger features determined for fsst3 and/or human SRIF receptors (hsst2, hsst3 and hsst5). 2 The GTP analogue guanylylimidodiphosphate (GppNHp) inhibited binding of [125I]CGP 23996 and [125I][Tyr3octreotide by 72 and 83% suggesting preferential labelling of G-protein-coupled fsst3 receptors. By contrast, [125I]LTT-SRIF28 and [125I][Tyr10]CST14 binding was rather GppNHp insensitive (42 and 35% inhibition) suggesting labelling of both coupled and non-coupled receptor states. These results might explain the apparent higher receptor densities determined in saturation experiments with [125I]LTT-SRIF28 and [125I][Tyr10]CST14 (4470 and 4030 fmol mg(-1)) compared with [125I]CGP 23996 and [125I][Tyr3]octreotide (3420 and 1520 fmol mg(-1)). 3 SRIF14 (10 microm)-stimulated specific [35S]GTPgammaS binding by three-fold; SRIF28 and octreotide displayed full agonism, whereas most other ligands displayed 60-80% intrinsic activity compared with SRIF14. SRIF14 and SRIF28 inhibited forskolin-stimulated AC (FSAC) activity by 60%; all tested ligands except BIM 23056 inhibited FSAC with comparable high intrinsic activities. SRIF14 stimulated PLC activity five- to six-fold, as determined by measuring total [3H] IP(x) accumulation; it was rather insensitive to pertussis toxin (PTX, 100 ng ml(-1), 21% inhibition), which suggests the G(q)-family proteins couple to PLC activity. SRIF14, SRIF28 and [Tyr10]CST14 showed full agonism at PLC, whereas all other ligands behaved as partial agonists (20-70% intrinsic activity). BIM 23056, which showed weak partial or no agonism, antagonized SRIF14-induced total [3H]-IP(x) production (pK(B) = 6.83), but failed to block competitively agonist-stimulated [35S]GTPgammaS binding or agonist-induced inhibition of FSAC activity. 4 Comparison of the pharmacological profiles of fsst3 receptors established in GTPgammaS binding, FSAC inhibition and PLC stimulation resulted in low correlations (r = 0.410-0.594). Both rank orders of potency and rank orders of relative efficacy varied in the three second messenger experiments. Significant, although variable correlations were obtained comparing GTPgammaS binding and inhibition of FSAC activity with previously reported affinity profiles of [125I]LTT-SRIF28, [125I][Tyr10]CST14, [125I]CGP 23996, [125I][Tyr3]octreotide (r = 0.75-0.83; 0.68-0.89). By contrast, the PLC stimulation and radioligand-binding profiles did not correlate. 5 Comparison of the functional data (GTPgammaS binding, FSAC inhibition, PLC stimulation) of fsst3 receptors with those of human sst2, sst3, sst5 receptors expressed in CCL39 cells resulted in highest correlation with the hsst5 receptor (r = 0.94, 0.97, 0.49) > hsst2 (0.80, 0.50, n.d.) > hsst3 (0.25, 0.19, 0.17). 6 In summary, fsst3 receptors expressed in CCL39 cells are involved in signalling cascades similar to those reported for mammalian SRIF receptors, suggesting SRIF receptors to be highly conserved in evolution. Binding and functional data showed highest similarity of fsst3 receptors with the human sst5 receptor subtype. Different affinities, receptor densities and GppNHp-sensitivities determined with the four radioligands (agonists) are assumed to results from ligand-specific states of the fsst3-ligand complex. The differences in the rank orders of potency and relative efficacy in the various signalling cascades may be explained by agonist-induced receptor trafficking.

Effect of cigarette smoke exposure in vivo on bronchial smooth muscle contractility in vitro in rats

Cigarette smoking is a risk factor for the development of airway hyperresponsiveness and chronic obstructive pulmonary disease. Little is known concerning the effect of cigarette smoking on the contractility of airway smooth muscle. The current study was performed to determine the responsiveness of bronchial smooth muscles isolated from rats that were subacutely exposed to mainstream cigarette smoke in vivo. Male Wistar rats were exposed to diluted mainstream cigarette smoke for 2 h/d every day for 2 wk. Twenty-four hours after the last cigarette smoke exposure, a marked airway inflammation (i.e., increases in numbers of neutrophils, lymphocytes, and macrophages in bronchoalveolar lavage fluid and peribronchial tissues) was observed. In these subacutely cigarette smoke-exposed animals, the responsiveness of isolated intact (nonpermeabilized) bronchial smooth muscle to acetylcholine, but not to high K+ -depolarization, was significantly augmented when compared with the air-exposed control group. In alpha-toxin-permeabilized bronchial smooth muscle strips, the acetylcholine-induced Ca2+ sensitization of contraction was significantly augmented in rats exposed to cigarette smoke, although the contraction induced by Ca2+ was control level. Immunoblot analyses revealed an increased expression of RhoA protein in the bronchial smooth muscle of rats that were exposed to cigarette smoke. Taken together, these findings suggest that the augmented agonist-induced, RhoA-mediated Ca2+ sensitization may be responsible for the enhanced bronchial smooth muscle contraction induced by cigarette smoking, which has relevance to airway hyperresponsiveness in patients with chronic obstructive pulmonary disease.

An electrophysiological study of excitatory purinergic neuromuscular transmission in longitudinal smooth muscle of chicken anterior mesenteric artery

1. The object of the present study was to clarify the neurotransmitters controlling membrane responses to electrical field stimulation (EFS) in the longitudinal smooth muscle cells of the chicken anterior mesenteric artery. 2. EFS (5 pulses at 20 Hz) evoked a depolarization of amplitude 19.7+/-2.1 mV, total duration 29.6+/-3.1 s and latency 413.0+/-67.8 ms. This depolarization was tetrodotoxin (TTX)-sensitive and its amplitude was partially decreased by atropine (0.5 microM); however, its duration was shortened by further addition of prazosin (10 microM). 3. Atropine/prazosin-resistant component was blocked by the nonspecific purinergic antagonist, suramin, in a dose-dependent manner, indicating that this component is mediated by the neurotransmitter adenosine 5'-triphosphate (ATP). 4. Neither desensitization nor blocking of P2X receptor with its putative receptor agonist alpha,beta-methylene ATP (alpha,beta-MeATP, 1 microM) and its antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic (PPADS, up to 50 microM), had significant effect on the purinergic depolarization. In contrast, either desensitization or blocking of P2Y receptor with its putative agonist 2-methylthioATP (2-MeSATP, 1 microM) and its antagonist Cibacron blue F3GA (CBF3GA, 10 microM) abolished the purinergic depolarization, indicating that this response is mediated through P2Y but not P2X receptor. 5. The purinergic depolarization was inhibited by pertussis toxin (PTX, 600 ng ml(-1)). Furthermore, it was significantly inhibited by a phospholipase C (PLC) inhibitor, U-73122 (10 microM), indicating that the receptors involved in mediating the purinergic depolarization are linked to a PTX-sensitive G-protein, which is involved in a PLC-mediated signaling pathway. 6. Data of the present study suggest that the EFS-induced excitatory membrane response occurring in the longitudinal smooth muscle of the chicken anterior mesenteric artery is mainly purinergic in nature and is mediated via P2Y purinoceptors.

Src homology domains in phospholipase C-gamma1 mediate its anti-apoptotic action through regulating the enzymatic activity

Phospholipase-gamma1 (PLC-gamma1) prevents programmed cell death, for which the enzymatic activity has been implicated. However, the biological function of Src homology (SH) domains of PLC-gamma1 in promoting cell survival remains elusive. Here, we showed that deletion of the N-SH2 domain or both N-SH2 and C-SH2 domains, but not the SH3 domain, abolished the anti-apoptotic activity of PLC-gamma1. Surprisingly, removal of the whole SH domain inhibited apoptosis. The lipase-inactive PLC-gamma1 mutant (LIM) failed to suppress apoptosis. Moreover, the phospholipase activity in SH3- or whole SH domain-deleted cells was comparable to that of wild-type cells. By contrast, the enzymatic activity was substantially ablated in SH2 domain-deleted or LIM cells. A pharmacological inhibitor of PLC-gamma1 robustly diminished the anti-apoptotic action in wild-type, SH3- or whole SH domain-deleted cells, whereas pretreatment of SH2 domain-deleted or LIM cells with agents activating PKC and calcium mobilization markedly promoted cell survival. These results indicate that SH domains in PLC-gamma1 might mediate its anti-apoptotic action by regulating the enzymatic activity.

A cellular deficiency of gangliosides causes hypersensitivity to Clostridium perfringens phospholipase C

Clostridium perfringens phospholipase C (Cp-PLC), also called alpha-toxin, is the major virulence factor in the pathogenesis of gas gangrene. Previously, a cellular UDP-Glc deficiency was related with a hypersensitivity to the cytotoxic effect of Cp-PLC. Because UDP-Glc is required in the synthesis of proteoglycans, N-linked glycoproteins, and glycosphingolipids, the role of these gly-coconjugates in the cellular sensitivity to Cp-PLC was studied. The cellular sensitivity to Cp-PLC was significantly enhanced by glycosphingolipid synthesis inhibitors, and a mutant cell line deficient in gangliosides was found to be hypersensitive to Cp-PLC. Gangliosides protected hypersensitive cells from the cytotoxic effect of Cp-PLC and prevented its membrane-disrupting effect on artificial membranes. Removal of sialic acids by C. perfringens sialidase increases the sensitivity of cultured cells to Cp-PLC and intramuscular co-injection of C. perfringens sialidase, and Cp-PLC in mice potentiates the myotoxic effect of the latter. This work demonstrated that a reduction in gangliosides renders cells more susceptible to the membrane damage caused by Cp-PLC and revealed a previously unrecognized synergism between Cp-PLC and C. perfringens sialidase, providing new insights toward understanding the pathogenesis of clostridial myonecrosis.

Inhibition of carbachol-evoked oscillatory currents by the NO donor sodium nitroprusside in guinea-pig ileal myocytes

The effect of sodium nitroprusside (SNP) on carbachol (CCh)-evoked inward cationic current (Icat) oscillations in guinea-pig ileal longitudinal myocytes was investigated using the whole-cell patch-clamp technique and permeabilized longitudinal muscle strips. SNP (10 microm) completely inhibited I(cat) oscillations evoked by 1 microm CCh. 1H-(1,2,4) Oxadiazole [4,3-a] quinoxaline-1-one (ODQ; 1 microm) almost completely prevented the inhibitory effect of SNP on Icat oscillations. 8-Bromo-guanosine 3',5'-cyclic monophosphate (8-Br-cGMP; 30 microm) in the pipette solution completely abolished Icat oscillations. However, a pipette solution containing Rp-8-Br-cGMP (30 microm) almost completely abolished the inhibitory effect of SNP on Icat oscillations. When the intracellular calcium concentration ([Ca2+]i) was held at a resting level using BAPTA (10 mm) and Ca2+ (4.6 microm) in the pipette solution, CCh (1 microm) evoked only the sustained component of Icat without any oscillations and SNP did not affect the current. A high concentration of inositol 1,4,5-trisphosphate (IP3; 30 microm) in the patch pipette solutions significantly reduced the inhibitory effect of SNP (10 microm) on Icat oscillations. SNP significantly inhibited the Ca2+ release evoked by either CCh or IP3 but not by caffeine in permeabilized preparations of longitudinal muscle strips. These results suggest that the inhibitory effects of SNP on Icat oscillations are mediated, in part, by functional modulation of the IP3 receptor, and not by the inhibition of cationic channels themselves or by muscarinic receptors in the plasma membrane. This inhibition seems to be mediated by an increased cGMP concentration in a protein kinase G-dependent manner.

Acetylcholine-induced phosphorylation of CPI-17 in rat bronchial smooth muscle: the roles of Rho-kinase and protein kinase C

It has been demonstrated that CPI-17 provokes an inhibition of myosin light chain phosphatase to increase myosin light chain phosphorylaton and Ca2+sensitivity during contraction of vascular smooth muscle. However, expression and agonist-mediated regulation of CPI-17 in bronchial smooth muscle have not been documented. Thus, expression and phosphorylation of CPI-17 mediated by PKC and ROCK were investigated using rat bronchial preparations. Acetylcholine (ACh)-induced contraction and Ca2+sensitization were both attenuated by 10–6mol Y-27632 /L, a ROCK inhibitor, 10–6mol calphostin C/L, a PKC inhibitor, and their combination. A PKC activator, PDBu, induced a Ca2+sensitization in α-toxin-permeabilized bronchial smooth muscle. In this case, the Ca2+sensitizing effect was significantly inhibited by caphostin C but not by Y-27632. An immunoblot study demonstrated CPI-17 expression in the rat bronchial smooth muscle. Acetylcholine induced a phosphorylation of CPI-17 in a concentration-dependent manner, which was significantly inhibited by Y-27632 and calphostin C. In conclusion, these data suggest that both PKC and ROCK are involved in force development, Ca2+sensitization, and CPI-17 phosphorylation induced by ACh stimulation in rat bronchial smooth muscle. As such, RhoA/ROCK, PKC/CPI-17, and RhoA/ROCK/CPI pathways may play important roles in the ACh-induced Ca2+sensitization of bronchial smooth muscle contraction.Key words: CPI-17, bronchial smooth muscle, acetylcholine, ROCK, protein kinase C.

G-protein-activated phospholipase C-β, new partners for cell polarity proteins Par3 and Par6

Cell polarity and asymmetric cell division are fundamental traits of all living cells and play an essential role in embryonic development, neuronal cell chirality formation, and maintenance of mammalian epithelial cell morphology. Heterotrimeric GTP-binding proteins (G proteins) are involved in directing cell polarity and asymmetric cell division in different organisms. However, the mechanism for G-protein-mediated cell polarity and asymmetric cell division is poorly understood. In this study, we have demonstrated that G-protein-activated phospholipase C-beta (PLC-beta) interacts with cell polarity proteins Par3 and Par6 (Par: partition-defective) to form protein complexes and to mediate downstream signal transduction. The interactions between PLC-beta and Par proteins are direct and require the extreme C-terminal-specific sequence motifs of PLC-beta and the PDZ (PSD95/Dlg/ZO-1) domains of Par proteins. Binding of Par proteins with PLC-beta stimulates PLC-beta enzymatic activity, leading to the hydrolysis of phosphatidylinositol-4,5-bisphosphate, and the production of diacylglycerol and inositol 1,4,5-triphosphate, important mediators in cell polarity and cell asymmetric division processes. Furthermore, we have shown that coexpression of PLC-beta with Par proteins induces transcriptional activation coupled to intracellular Ca2+ and the Wnt signaling pathway. Therefore, our data suggest that the interaction of PLC-beta with cell polarity Par proteins may serve as a nexus to transduce extracellular signals to transcriptional regulation through G-protein-mediated signaling pathway in cell polarity and cell asymmetric division.

Mechanotransduction by integrin is essential for IL-6 secretion from endothelial cells in response to uniaxial continuous stretch

We previously reported that uniaxial continuous stretch in human umbilical vein endothelial cells (HUVECs) induced interleukin-6 (IL-6) secretion via IkappaB kinase (IKK)/nuclear factor-kappaB (NF-kappaB) activation. The aim of the present study was to clarify the upstream signaling mechanism responsible for this phenomenon. Stretch-induced IKK activation and IL-6 secretion were inhibited by application of alpha(5)beta(1) integrin-inhibitory peptide (GRGDNP), phosphatidylinositol 3-kinase inhibitor (LY-294002), phospholipase C-gamma inhibitor (U-73122), or protein kinase C inhibitor (H7). Although depletion of intra- or extracellular Ca(2+) pool using thapsigargin (TG) or EGTA, respectively, showed little effect, a TG-EGTA mixture significantly inhibited stretch-induced IKK activation and IL-6 secretion. An increase in the intracellular Ca(2+) concentration ([Ca(2+)](i)) upon continuous stretch was observed even in the presence of TG, EGTA, or GRGDNP, but not in a solution containing the TG-EGTA mixture, indicating that both integrin activation and [Ca(2+)](i) rise are crucial factors for stretch-induced IKK activation and after IL-6 secretion in HUVECs. Furthermore, while PKC activity was inhibited by the TG-EGTA mixture, GRGDNP, LY-294002, or U-73122, PLC-gamma activity was retarded by GRGDNP or LY-294002. These results indicate that continuous stretch-induced IL-6 secretion in HUVECs depends on outside-in signaling via integrins followed by a PI3-K-PLC-gamma-PKC-IKK-NF-kappaB signaling cascade. Another crucial factor, [Ca(2+)](i) increase, may at least be required to activate PKC needed for NF-kappaB activation.

Role for the Kunitz-3 domain of tissue factor pathway inhibitor-alpha in cell surface binding

BACKGROUND

Tissue factor pathway inhibitor (TFPI)-alpha, a key regulator of tissue factor-induced coagulation, contains 3 tandem Kunitz-type inhibitory domains. Kunitz-1 binds and inhibits factor VIIa in the factor VIIa/tissue factor complex, and Kunitz-2 binds and inhibits factor Xa. The role of the Kunitz-3 domain of TFPI-alpha, however, has remained an enigma.

METHODS AND RESULTS

To determine the structures within TFPI-alpha involved in its binding to cell surface, altered forms of TFPI-alpha were expressed in C127 (mouse mammary) cells: C-terminal truncated forms TFPI-alpha (252), TFPI-alpha (242), and TFPI-alpha (181), which also lacks the third Kunitz domain (K3); TFPI-alpha (desK3), which lacks only the K3 domain; and TFPI-alpha (R199L), in which the putative P1 site in K3 is changed from arginine to leucine. By flow cytometry (fluorescence-activated cell sorting), the altered forms 252, 242, and R199L showed significantly reduced binding, whereas the forms 181 and desK3 completely failed to bind to the cell surface. Transient expression of WT-, desK3-, and K3/K2-TFPI-alpha (in which K3 is replaced with K2) in another cell line (b-end3, mouse endothelial) produced comparable results. Exogenously added C-terminal truncated and R199L forms of TFPI-alpha bound poorly and desK3 did not bind at all to the surface of ECV304 cells in which TFPI-alpha expression had been "knocked down" by RNA interference.

CONCLUSIONS

Optimal cell binding of endogenously expressed TFPI-alpha requires its K3 and C-terminal domains, and within the K3 domain, the P1 (R199) residue plays an important role. Thus, one role of the K3 domain involves the cell surface localization of TFPI-alpha.

Lysophosphatidic acid induces hypertrophy of neonatal cardiac myocytes via activation of Gi and Rho

The effect of the lysophospholipid, lysophosphatidic acid (LPA), on signaling and hypertrophy of neonatal rat ventricular cardiomyocytes was examined. Myocytes express mRNA for all three G-protein-coupled LPA receptor subtypes (LPA(1)/Edg-2, LPA(2)/Edg-4, and LPA(3)/Edg-7) as indicated by RT-PCR analysis. LPA inhibits isoproterenol-stimulated cyclic AMP accumulation with an IC(50) approximately 40 nM and promotes phosphorylation of ERK-1/2. LPA also elicits a small, slow onset, and activation of phosphoinositide hydrolysis with EC(50) approximately 400 nM, and stimulates a marked increase in the extent of Rho activation. Longer-term treatment with LPA induces a hypertrophic response in myocytes as indicated by increases in cell size, actin organization, ANF staining of the perinuclear region and activation of ANF promoter-luciferase gene expression. Pretreatment of myocytes with pertussis toxin (PTX) not only blocks the capacity of LPA to inhibit cyclic AMP formation and stimulate ERK phosphorylation, but also inhibits hypertrophic changes in cell morphology and ANF-luciferase gene expression. Neither phospholipase C nor Rho activation is PTX sensitive. The hypertrophic effects of LPA on myocytes are also inhibited by treatment with C3 exoenzyme or by transfection of plasmids expressing either C3 exoenzyme or dominant-negative Rho to block Rho function. Inhibition of ERK activation with PD98059 blocks LPA-induced hypertrophy while inhibitors of phospholipase C (U73122), PKC (GF109203X), or p38MAPK (SB203580) do not. These data suggest that LPA induces cardiomyocyte hypertrophy via a pathway different from the conventional G(q) pathway utilized by phenylephrine, endothelin, and PGF2 alpha and involving activation of a PTX-sensitive G(i)/ERK pathway in conjunction with activation of Rho-mediated signals.

Clostridium perfringens alpha-toxin: characterization and mode of action

Clostridium perfringens type A strains that produce alpha-toxin cause gas gangrene, which is a life-threatening infection with fever, pain, edema, myonecrosis and gas production. Intramuscular injection of the toxin or Bacillus subtilis carrying the alpha-toxin gene causes myonecrosis and produces histopathological features of the disease. Immunization of mice with alpha-toxin or fragments of the toxin prevents gas gangrene caused by C. perfringens. The toxin possesses phospholipase C (PLC), sphingomyelinase (SMase) and biological activities causing hemolysis, lethality and dermonecrosis. These biological activities are closely related to PLC and/or SMase activities. However, there is yet some uncertainty about the biological activities induced by the PLC and SMase activities of alpha-toxin. Based on the isolation and characterization of the gene for alpha-toxin and a comparison of the toxin with enzymes of the PLC family, significant progress has been made in determining the function-structure of alpha-toxin and the mode of action of the toxin. To provide a better understanding of the role of alpha-toxin in tissue damage in gas gangrene, this article summarizes current knowledge of the characteristics and mode of action of alpha-toxin.

Contribution of lipid second messengers to the regulation of phosphatidylcholine synthesis during cell cycle re-entry

During entry into the cell cycle a phosphatidylcholine (PC) metabolic cycle is activated. We have examined the hypothesis that PC synthesis during the G(0) to G(1) transition is controlled by one or more lipid products of PC turnover acting directly on the rate-limiting enzyme in the synthesis pathway, CTP: phosphocholine cytidylyltransferase (CCT). The acceleration of PC synthesis was two- to threefold during the first hour after addition of serum to quiescent IIC9 fibroblasts. The rate increased to approximately 15-fold above the basal rate during the second hour. The production of arachidonic acid, diacylglycerol (DAG), and phosphatidic acid (PA) preceded the second, rapid phase of PC synthesis. However, an increase in the cellular content of these lipid mediators was detected only for DAG. CCT activation and translocation to membranes accompanied the second phase of the PC synthesis acceleration. Bromoenol lactone (BEL), an inhibitor of calcium-independent phospholipase A(2) and PA phosphatase, blocked production of fatty acids and DAG, inhibited both phases of the PC synthesis response to serum, and reduced CCT activity and membrane affinity. The effect of BEL on PC synthesis was partially reversed by in situ generation of DAG via exogenous PC-specific phospholipase C to generate approximately 2-fold elevation in PC-derived DAG. Exogenous arachidonic acid also partially reversed the inhibition by BEL, but only at a concentration that generated a supra-physiological cellular content of free fatty acid. 1-Butanol, which blocks PA production, had no effect on DAG generation, or on PC synthesis. We conclude that fatty acids and DAG could contribute to the initial slow phase of the PC synthesis response. DAG is the most likely lipid regulator of CCT activity and the rapid phase of PC synthesis. However, processes other than direct activation of CCT by lipid mediators likely contribute to the highly accelerated phase during entry into the cell cycle.

Mechanisms involved in the antiplatelet activity of rutin, a glycoside of the flavonol quercetin, in human platelets

The aim of this study was to systematically examine the inhibitory mechanisms of rutin, a well-known flavonoid in platelet aggregation. In this study, rutin concentration-dependently (250 and 290 microM) inhibited platelet aggregation in human platelets stimulated by agonists (i.e., collagen). Rutin (250 and 290 microM) did not significantly interfere with the binding of FITC-triflavin to the glycoprotein IIb/IIIa complex in human platelets. Rutin (250 and 290 microM) markedly inhibited intracellular Ca(2+) mobilization and thromboxane A(2) formation in human platelets stimulated by collagen. Rapid phosphorylation of a platelet protein of M(r) 47000 (P47), a marker of protein kinase C activation, was triggered by collagen (1 microg/mL). This phosphorylation was markedly inhibited by rutin (250 and 290 microM). On the other hand, rutin (250 and 290 microM) did not significantly increase the formations of cyclic AMP and nitric oxide/cyclic GMP in platelets. In conclusion, these results indicate that the antiplatelet activity of rutin may involve the following pathways: rutin inhibited the activation of phospholipase C, followed by inhibition of protein kinase C activity and thromboxane A(2) formation, thereby leading to inhibition of the phosphorylation of P47 and intracellular Ca(2+) mobilization, finally resulting in inhibition of platelet aggregation.

Calmodulin-mediated activation of Akt regulates survival of c-Myc-overexpressing mouse mammary carcinoma cells

c-Myc-overexpressing mammary epithelial cells are proapoptotic; their survival is strongly promoted by epidermal growth factor (EGF). We now demonstrate that EGF-induced Akt activation and survival in transgenic mouse mammary tumor virus-c-Myc mouse mammary carcinoma cells are both calcium/calmodulin-dependent. Akt activation is abolished by the phospholipase C-gamma inhibitor U-73122, by the intracellular calcium chelator BAPTA-AM, and by the specific calmodulin antagonist W-7. These results implicate calcium/calmodulin in the activation of Akt in these cells. In addition, Akt activation by serum and insulin is also inhibited by W-7. EGF-induced and calcium/calmodulin-mediated Akt activation occurs in both tumorigenic and non-tumorigenic mouse and human mammary epithelial cells, independent of their overexpression of c-Myc. These results imply that calcium/calmodulin may be a common regulator of Akt activation, irrespective of upstream receptor activator, mammalian species, and transformation status in mammary epithelial cells. However, only c-Myc-overexpressing mouse mammary carcinoma cells (but not normal mouse mammary epithelial cells) undergo apoptosis in the presence of the calmodulin antagonist W-7, indicating the vital selective role of calmodulin for survival of these cells. Calcium/calmodulin-regulated Akt activation is mediated directly by neither calmodulin kinases nor phosphatidylinositol 3-kinase (PI-3 kinase). Pharmacological inhibitors of calmodulin kinase kinase and calmodulin kinases II and III do not inhibit EGF-induced Akt activation, and calmodulin antagonist W-7 does not inhibit phosphotyrosine-associated PI-3 kinase activation. Akt is, however, co-immunoprecipitated with calmodulin in an EGF-dependent manner, which is inhibited by calmodulin antagonist W-7. We conclude that calmodulin may serve a vital regulatory function to direct the localization of Akt to the plasma membrane for its activation by PI-3 kinase.

Dependence of Ca2+-induced contraction on ATP in alpha-toxin-permeabilized preparations of rat femoral artery

Effects of various concentrations of ATP on Ca(2+)-induced contraction were studied in alpha-toxin-permeabilized preparations obtained from the rat femoral artery. The contractile magnitude was highest in the presence of 1 mM ATP and decreased with both increasing and decreasing the concentration, suggesting the presence of an optimum ATP concentration in inducing contraction. The magnitude of the contractions in various concentrations of ATP correlated with the extent of the phosphorylated myosin light chain (MLC). The rate of contractions in the presence of 1 mM ATP under an inhibition of MLC phosphatase was faster than in the presence of 4 mM ATP, suggesting that the increased phosphorylation of MLC at 1 mM ATP results from an increased activity of MLC kinase. On the other hand, MLC phosphatase activity appeared unchanged, because the rates of relaxations under the inhibition of MLC kinase were not different in the presence of either 1 or 4 mM ATP. The high sensitivity to 1 mM ATP was absent in the preparations that were permeabilized with beta-escin or Triton X-100, suggesting the existence of an intracellular factor required for the increased activity of MLC kinase to ATP in the alpha-toxin-permeabilized preparations of the rat femoral artery.

First chemical synthesis of a scorpion α-toxin affecting sodium channels: The Aah I toxin ofAndroctonus australis hector

Aah I is a 63-residue alpha-toxin isolated from the venom of the Buthidae scorpion Androctonus australis hector, which is considered to be the most dangerous species. We report here the first chemical synthesis of Aah I by the solid-phase method, using a Fmoc strategy. The synthetic toxin I (sAah I) was renatured in DMSO-Tris buffer, purified and subjected to thorough analysis and comparison with the natural toxin. The sAah I showed physico-chemical (CD spectrum, molecular mass, HPLC elution), biochemical (amino-acid composition, sequence), immunochemical and pharmacological properties similar to those of the natural toxin. The synthetic toxin was recognized by a conformation-dependent monoclonal anti-Aah I antibody, with an IC50 value close to that for the natural toxin. Following intracerebroventricular injection, the synthetic and the natural toxins were similarly lethal to mice. In voltage-clamp experiments, Na(v) 1.2 sodium channel inactivation was inhibited by the application of sAah I or of the natural toxin in a similar way. This work describes a simple protocol for the chemical synthesis of a scorpion alpha-toxin, making it possible to produce structural analogues in time.

Inhibition of ENaC by intracellular Cl- in an MDCK clone with high ENaC expression

We examined the effects of intracellular Cl- concentration ([Cl-]i) on the epithelial Na channel (ENaC) in a line of Madin-Darby canine kidney (MDCK) cells (FL-MDCK) with a high rate of Na+ transport produced by stable retroviral transfection with rENaC subunits (Morris RG and Schafer JA. J Gen Physiol 120: 71-85, 2002). Treatment with cAMP (100 microM 8-cpt-cAMP plus 100 microM IBMX) stimulated ENaC-mediated Na+ absorption as well as Cl- secretion via cystic fibrosis transmembrane conductance regulator, which was characterized in alpha-toxin-permeabilized monolayers to have the anion selectivity sequence NO3- > Br- > Cl- > I-. With the use of FL-MDCK monolayers in which the basolateral membrane was permeabilized by nystatin, the ENaC conductance of the apical membrane [determined from the amiloride-sensitive short-circuit current (AS-Isc) driven by an apical-to-basolateral Na+ concentration gradient] was progressively inhibited by increasing the [Cl-] in the basolateral solution (and hence in the cytosol), but it was insensitive to the [Cl-] in the apical solution. This inhibitory effect of [Cl-]i occurred regardless of the presence or absence of net Cl- transport. However, from fluorometric measurements using the Cl(-)-sensitive dye 6-methoxy-N-(3-sulfopropyl)-quinolinium in intact FL-MDCK monolayers on permeable supports, cAMP, which activates both Na+ absorption and Cl- secretion, produced a decrease of [Cl-]i from 76 +/- 14 to 36 +/- 8 mM (P = 0.03). Thus it might be expected that activation of Cl- secretion by cAMP would lead to stimulation rather than inhibition of ENaC. In the nystatin-treated monolayers, an increase in [Cl-]i from 15 to 145 mM decreased AS-Isc from 24.5 +/- 1.0 to 10.2 +/- 1.6 microA/cm2. This inhibition of ENaC could be attributed to nearly proportional decreases in the density of ENaC in the apical membrane from 1.91 +/- 0.16 to 1.32 +/- 0.17 fmol/cm2 and in the intrinsic channel activity (the average current per ENaC subunit) from 13.3 +/- 1.2 to 8.2 +/- 1.4 microA/fmol.

Mechanisms involved in carbachol-induced Ca(2+) sensitization of contractile elements in rat proximal and distal colon

1. Mechanisms involved in Ca(2+) sensitization of contractile elements induced by the activation of muscarinic receptors in membrane-permeabilized preparations of the rat proximal and distal colon were studied. 2. In alpha-toxin-permeabilized preparations from the rat proximal and distal colon, Ca(2+) induced a rapid phasic and subsequent tonic component. After Ca(2+)-induced contraction reached a plateau, guanosine 5'-triphosphate (GTP) and carbachol (CCh) in the presence of GTP further contracted preparations of both the proximal and distal colon (Ca(2+) sensitization). Y-27632, a rho-kinase inhibitor, inhibited GTP plus CCh-induced Ca(2+) sensitization more significantly in the proximal colon than in the distal colon. 3. Y-27632 at 10 microm had no effect on Ca(2+)-induced contraction or slightly inhibited phorbol-12,13-dibutyrate-induced Ca(2+) sensitization in either proximal or distal colon. Chelerythrine, a protein kinase C inhibitor, inhibited GTP plus CCh-induced Ca(2+) sensitization in the distal colon, but not in the proximal colon. The component of Ca(2+) sensitization that persisted after the chelerythrine treatment was completely inhibited by Y-27632. 4. In beta-escin-permeabilized preparations of the proximal colon, C3 exoenzyme completely inhibited GTP plus CCh-induced Ca(2+) sensitization, but PKC(19-31) did not. In the distal colon, C3 exoenzyme abolished GTP-induced Ca(2+) sensitization. It inhibited CCh-induced sensitization by 50 % and the remaining component was inhibited by PKC(19-31). 5. These results suggest that both protein kinase C and rho pathways in parallel mediate the Ca(2+) sensitization coupled to activation of muscarinic receptors in the rat distal colon, whereas the rho pathway alone mediates this action in the proximal colon.

EphA/ephrin-A interactions during optic nerve regeneration: restoration of topography and regulation of ephrin-A2 expression

During visual system development, interactions between Eph tyrosine kinase receptors and their ligands, the ephrins, guide retinal ganglion cell (RGC) axons to their topographic targets in the optic tectum. Here we show that Eph/ephrin interactions are also involved in restoring topography during RGC axon regeneration in goldfish. Following optic nerve crush, EphA/ephrin-A interactions were blocked by intracranial injections of recombinant Eph receptor (EphA3-AP) or phospho-inositol phospholipase-C. Topographic errors with multiple inputs to some tectal loci were detected electrophysiologically and increased projections to caudal tectum demonstrated by RT-97 immunohistochemistry. In EphA3-AP-injected fish, ephrin-A2-expressing cells in the retino-recipient tectal layers were reduced in number compared to controls and their distribution was no longer graded. The findings, supported by in vitro studies, implicate EphA/ephrin-A interactions in restoring precise topography and in regulating ephrin-A2 expression during regeneration.

Evidence for the Involvement of Protein Kinase C in Acidic pH-Induced Contraction in Spontaneously Hypertensive Rat Aorta

This study was performed to test the hypothesis that activation of protein kinase C (PKC) is a mechanism underlying the acidic pH-induced contraction (APIC) in spontaneously hypertensive rat (SHR) aorta. Changing pH of the bathing solution from 7.4 to 6.5 induced a marked contraction of SHR aorta. PKC inhibitors, GF109203X and calphostin C markedly inhibited the APIC selectively, without having a marked effect on the KCl-induced contraction. Inhibitors of mitogen-activated protein kinase kinase, U0126 and PD98059 mildly but significantly attenuated the APIC. However, at the similar concentrations both U0126 and PD98059 inhibited the KCl-induced contraction in a manner similar to that observed in APIC. D-609, an inhibitor of phosphatidylcholine-specific phospholipase C (PC-PLC) markedly inhibited the APIC and the extent of inhibition by this compound was similar to that shown by PKC inhibitors. Whereas, U-73122 and propranolol, inhibitors of phosphatidylinositol-specific PLC and phosphatidate phosphohydrolase, respectively, had no affect on the APIC. A tyrosine kinase inhibitor, tyrphostin 23 and GF109203X inhibited the APIC in an additive manner, and together they abolished the contractile response. From all these results, it is suggested that a significant component of the contraction observed in response to acidosis in SHR aorta is dependent upon the activation of PKC that seems to be the downstream event of the activation of PC-PLC. Furthermore, PKC- and tyrosine kinase-dependent pathways underlying the APIC are independent of each other.