Involvement of tyrosine phosphorylation in endothelin-1-induced calcium-sensitization in rat small mesenteric arteries

Role of src-family kinases in hypoxic vasoconstriction of rat pulmonary artery

Aims

We investigated the role of src-family kinases (srcFKs) in hypoxic pulmonary vasoconstriction (HPV) and how this relates to Rho-kinase-mediated Ca²⁺ sensitization and changes in intracellular Ca²⁺ concentration ([Ca²⁺]_i).

Methods and results

Intra-pulmonary arteries (IPAs) were obtained from male Wistar rats. HPV was induced in myograph-mounted IPAs. Auto-phosphorylation of srcFKs and phosphorylation of the regulatory subunit of myosin phosphatase (MYPT-1) and myosin light-chain (MLC₂₀) in response to hypoxia were determined by western blotting. Translocation of Rho-kinase and effects of siRNA knockdown of src and fyn were examined in cultured pulmonary artery smooth muscle cells (PASMCs). [Ca²⁺]_i was estimated in Fura-PE3-loaded IPA. HPV was inhibited by two blockers of srcFKs, SU6656 and PP2. Hypoxia enhanced phosphorylation of three srcFK proteins at Tyr-416 (60, 59, and 54 kDa, corresponding to src, fyn, and yes, respectively) and enhanced srcFK-dependent tyrosine phosphorylation of multiple target proteins. Hypoxia caused a complex, time-dependent enhancement of MYPT-1 and MLC₂₀ phosphorylation, both in the absence and presence of pre-constriction. The sustained component of this enhancement was blocked by SU6656 and the Rho-kinase inhibitor Y27632. In PASMCs, hypoxia caused translocation of Rho-kinase from the nucleus to the cytoplasm, and this was prevented by anti-src siRNA and to a lesser extent by anti-fyn siRNA. The biphasic increases in [Ca²⁺]_i that accompany HPV were also inhibited by PP2.

Conclusion

Hypoxia activates srcFKs and triggers protein tyrosine phosphorylation in IPA. Hypoxia-mediated Rho-kinase activation, Ca²⁺ sensitization, and [Ca²⁺]_i responses are depressed by srcFK inhibitors and/or siRNA knockdown, suggesting a central role of srcFKs in HPV.

Reactive oxygen species mediate RhoA/Rho kinase-induced Ca2+ sensitization in pulmonary vascular smooth muscle following chronic hypoxia

Recent evidence supports a prominent role for Rho kinase (ROK)-mediated pulmonary vasoconstriction in the development and maintenance of chronic hypoxia (CH)-induced pulmonary hypertension. Endothelin (ET)-1 contributes to the pulmonary hypertensive response to CH, and recent studies by our laboratory and others indicate that pulmonary vascular reactivity following CH is largely independent of changes in vascular smooth muscle (VSM) intracellular free calcium concentration ([Ca(2+)](i)). In addition, CH increases generation of reactive oxygen species (ROS) in pulmonary arteries, which may underlie the shift toward ROK-dependent Ca(2+) sensitization. Therefore, we hypothesized that ROS-dependent RhoA/ROK signaling mediates ET-1-induced Ca(2+) sensitization in pulmonary VSM following CH. To test this hypothesis, we determined the effect of pharmacological inhibitors of ROK, myosin light chain kinase (MLCK), tyrosine kinase (TK), and PKC on ET-1-induced vasoconstriction in endothelium-denuded, Ca(2+)-permeabilized small pulmonary arteries from control and CH (4 wk at 0.5 atm) rats. Further experiments examined ET-1-mediated, ROK-dependent phosphorylation of the regulatory subunit of myosin light chain phosphatase (MLCP), MYPT1. Finally, we measured ET-1-induced ROS generation in dihydroethidium-loaded small pulmonary arteries and investigated the role of ROS in mediating ET-1-induced, RhoA/ROK-dependent Ca(2+) sensitization using the superoxide anion scavenger, tiron. We found that CH increases ET-1-induced Ca(2+) sensitization that is sensitive to inhibition of ROK and MLCK, but not PKC or TK, and correlates with ROK-dependent MYPT1(Thr696) phosphorylation. Furthermore, tiron inhibited basal and ET-1-stimulated ROS generation, RhoA activation, and VSM Ca(2+) sensitization following CH. We conclude that CH augments ET-1-induced Ca(2+) sensitization through ROS-dependent activation of RhoA/ROK signaling in pulmonary VSM.

Phospholipase C-delta1 modulates sustained contraction of rat mesenteric small arteries in response to noradrenaline, but not endothelin-1

Vasoconstrictors activate phospholipase C (PLC), which hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP(2)), leading to calcium mobilization, protein kinase C activation, and contraction. Our aim was to investigate whether PLC-delta(1), a PLC isoform implicated in alpha(1)-adrenoreceptor signaling and the pathogenesis of hypertension, is involved in noradrenaline (NA) or endothelin (ET-1)-induced PIP(2) hydrolysis and contraction. Rat mesenteric small arteries were studied. Contractility was measured by pressure myography, phospholipids or inositol phosphates were measured by radiolabeling with (33)Pi or myo-[(3)H]inositol, and caveolae/rafts were prepared by discontinuous sucrose density centrifugation. PLC-delta(1) was localized by immunoblot analysis and neutralized by delivery of PLC-delta(1) antibody. The PLC inhibitor U73122, but not the negative control U-73342, markedly inhibited NA and ET-1 contraction but had no effect on potassium or phorbol ester contraction, implicating PLC activity in receptor-mediated smooth muscle contraction. PLC-delta(1) was present in caveolae/rafts, and NA, but not ET-1, stimulated a rapid twofold increase in PLC-delta(1) levels in these domains. PLC-delta(1) is calcium dependent, and removal of extracellular calcium prevented its association with caveolae/rafts in response to NA, concomitantly reducing NA-induced [(33)P]PIP(2) hydrolysis and [(3)H]inositol phosphate formation but with no effect on ET-1-induced [(33)P]PIP(2) hydrolysis. Neutralization of PLC-delta(1) by PLC-delta(1) antibody prevented its caveolae/raft association and attenuated the sustained contractile response to NA compared with control antibodies. In contrast, ET-1-induced contraction was not affected by PLC-delta(1) antibody. These results indicate the novel and selective role of caveolae/raft localized PLC-delta(1) in NA-induced PIP(2) hydrolysis and sustained contraction in intact vascular tissue.

Regulation of contractility by Hsp27 and Hic-5 in rat mesenteric small arteries

The regulation of small artery contractility by vasoconstrictors is important for vascular function, and actin cytoskeleton remodeling is required for contraction. p38 MAPK and tyrosine kinases are implicated in actin polymerization and contraction through heat shock protein 27 (Hsp27) and the cytoskeletal protein paxillin, respectively. We evaluated the roles of downstream targets of p38 MAPK and tyrosine kinases in cytoskeletal reorganization and contraction and whether the two signaling pathways regulate contraction independent of each other. We identified the expression of the paxillin homologue hydrogen peroxide-inducible clone-5 (Hic-5) and showed its activation by norepinephrine (NE) in a Src-dependent manner. Furthermore, we demonstrated a NE-induced interaction of proline-rich tyrosine kinase-2 (PYK2) but not Src or p125 focal adhesion kinase with Hic-5. This interaction was Src dependent, suggesting that Hic-5 was a substrate for PYK2 downstream from Src. The activation of Hic-5 induced its relocalization to the cytosol. The parallel activation of Hsp27 by NE was p38 MAPK dependent and led to its dissociation from actin filaments and translocation from membrane to cytosol and increased actin polymerization. Both Hsp27 and Hic-5 activation resulted in their association within the same time frame as NE-induced contraction, and the inhibition of either p38 MAPK or Src inhibited the interaction between Hsp27 and Hic-5 and the contractile response. Furthermore, combined p38 MAPK and Src inhibition had no greater effect on contraction than individual inhibition, suggesting that the two pathways act through a common mechanism. These data show that NE-induced activation and the association of Hsp27 and Hic-5 are required for the reorganization of the actin cytoskeleton and force development in small arteries.

Vasorelaxing effect of the Rho-kinase inhibitor, Y-27632, in isolated canine basilar arteries

OBJECTIVES

Increased calcium sensitization mediated by Rho/Rho-kinase may be important in the pathogenesis of cerebral vasospasm. The effects of a highly selective Rho-kinase inhibitor, Y-27632, were investigated on spasmogen-induced contractions of canine basilar artery.

METHODS

Typical spasmogenic substances present after subarachnoid hemorrhage (SAH), including prostaglandin F2a (PGF2a), 12-deoxyphorbol 13-isobutyrate (DPB), sphingosylpho-sphorylcholine (SPC) and high K+, were used in the study. Isometric tension was recorded in canine basilar artery rings in vitro. Intracellular calcium concentration ([Ca2+]i) and contraction force were measured simultaneously in fura-2-loaded canine basilar artery strips. The myosin light chain (MLC) phosphorylation levels were measured by glycerol gel electrophoresis followed by Western blotting.

RESULTS

Isometric tension recording revealed that the Rho-kinase inhibitor, Y-27632, dose-dependently inhibited vasocontraction induced by PGF2a and SPC, but not that induced by DPB. Simultaneous recordings of [Ca2+]i and tension revealed that the vasorelaxing effect of Y-27632 was not associated with changes in [Ca2+]i, suggesting that Y-27632 may inhibit calcium sensitization. Vasocontraction induced by DPB was not inhibited by Y-27632, but was inhibited by staurosporine. Phosphorylation of MLC was increased by PGF2a and SPC, and significantly inhibited by Y-27632, whereas such phosphorylation was increased by DPB, but not significantly inhibited by Y-27632.

DISCUSSION

Several spasmogenic mediators released after SAH may cause vasospasm through Rho-kinase-mediated increase in calcium sensitization. Rho-kinase inhibitors, including Y-27632, may be effective for the prevention of cerebral vasospasm after SAH.

Interaction between src family kinases and rho-kinase in agonist-induced Ca2+-sensitization of rat pulmonary artery

Aims

We investigated the role of src family kinases (srcFK) in agonist-mediated Ca²⁺-sensitization in pulmonary artery and whether this involves interaction with the rho/rho-kinase pathway.

Methods and results

Intra-pulmonary arteries (IPAs) and cultured pulmonary artery smooth muscle cells (PASMC) were obtained from rat. Expression of srcFK was determined at the mRNA and protein levels. Ca²⁺-sensitization was induced by prostaglandin F_2α (PGF_2α) in α-toxin-permeabilized IPAs. Phosphorylation of the regulatory subunit of myosin phosphatase (MYPT-1) and of myosin light-chain-20 (MLC₂₀) and translocation of rho-kinase in response to PGF_2α were also determined. Nine srcFK were expressed at the mRNA level, including src, fyn, and yes, and PGF_2α enhanced phosphorylation of three srcFK proteins at tyr-416. In α-toxin-permeabilized IPAs, PGF_2α enhanced the Ca²⁺-induced contraction (pCa 6.9) approximately three-fold. This enhancement was inhibited by the srcFK blockers SU6656 and PP2 and by the rho-kinase inhibitor Y27632. Y27632, but not SU6656 or PP2, also inhibited the underlying pCa 6.9 contraction. PGF_2α enhanced phosphorylation of MYPT-1 at thr-697 and thr-855 and of MLC₂₀ at ser-19. This enhancement, but not the underlying basal phosphorylation, was inhibited by SU6656. Y27632 suppressed both basal and PGF_2α-mediated phosphorylation. The effects of SU6656 and Y27632, on both contraction and MYPT-1 and MLC₂₀ phosphorylation, were not additive. PGF_2α triggered translocation of rho-kinase in PASMC, and this was inhibited by SU6656.

Conclusions

srcFK are activated by PGF_2α in the rat pulmonary artery and may contribute to Ca²⁺-sensitization and contraction via rho-kinase translocation and phosphorylation of MYPT-1.

Norepinephrine and endothelin activate diacylglycerol kinases in caveolae/rafts of rat mesenteric arteries: agonist-specific role of PI3-kinase

The phosphatidylinositol (PI) signaling pathway mediates norepinephrine (NE)- and endothelin-1 (ET-1)-stimulated vascular smooth muscle contraction through an inositol-trisphosphate-induced rise in intracellular calcium and diacylglycerol (DG) activation of protein kinase C (PKC). Subsequent activation of DG kinases (DGKs) metabolizes DG to phosphatidic acid (PA), potentially regulating PKC activity. Because precise regulation and spatial restriction of the PI pathway is necessary for specificity, we have investigated whether this occurs within caveolae/rafts, specialized plasma membrane microdomains implicated in vascular smooth muscle contraction. We show that components of the PI signaling cascade-phosphatidylinositol 4,5-bisphosphate (PIP(2)), PA, and DGK-theta are present in caveolae/rafts prepared from rat mesenteric small arteries. Stimulation with NE or ET-1 induced [(33)P]PIP(2) hydrolysis solely within caveolae/rafts. NE stimulated an increase in DGK activity in caveolae/rafts alone, whereas ET-1 activated DGK in caveolae/rafts and noncaveolae/rafts; however, [(33)P]PA increased in all fractions with both agonists. Previously, we reported that NE activated DGK-theta in a phosphatidylinositol 3-kinase (PI3-kinase)-dependent manner; here, we describe PI3-kinase-dependent DGK activation and [(33)P]PA production in caveolae/rafts in response to NE but not ET-1. Additionally, PKB, a potential activator of DGK-theta, translocated to caveolae/rafts in response to NE but not ET-1, and PI3-kinase inhibition prevented this. Furthermore, PI3-kinase inhibition reduced the sensitivity of contraction to NE but not ET-1. Our study shows that caveolae/rafts are major sites of vasoconstrictor hormone activation of the PI pathway in intact small arteries and suggest a link between lipid signaling events within caveolae/rafts and contraction.

Signal transduction of bombesin-induced circular smooth muscle cell contraction in cat esophagus

AIM: To investigate the mechanism of bombesin-induced circular smooth muscle cell contraction in cat esophagus.

METHODS: Specific G protein or phospholipase C involved in cat esophagus contraction was identified, muscle cells were permeabilized with saponin. After permeabilization of muscle cells, the Gi3 antibody inhibited bombesin-induced smooth muscle cell contraction.

RESULTS: Incubation of permeabilized circular muscle cells with PLC-β3 antibody could inhibit bombesin-induced contraction. H-7, chelerythrine (PKC inhibitor) and genistein (protein tyrosine kinase inhibitor) inhibited bombesin-induced contraction, but DAG kinase inhibitor, R59949, could not inhibit it. To examine which mitogen-activated protein kinase (MAPK) was involved in bombesin-induced contraction, the specific MAPK inhibitors (MEK inhibitor, PD98059 and p38 MAPK inhibitor, SB202190) were used. Preincubation of PD98059 blocked the contraction induced by bombesin in a concentration-dependent manner. However, SB202190 had no effects on contraction.

CONCLUSION: Bombesin-induced circular muscle cell contraction in cat esophagus is madiated via a PKC or a PTK-dependent pathway or p44/p42 MAPK pathway.

Protein kinases in vascular smooth muscle tone--role in the pulmonary vasculature and hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) is an adaptive mechanism that in the normal animal diverts blood away from poorly ventilated areas of the lung, thereby maintaining optimal ventilation-perfusion matching. In global hypoxia however, such as in respiratory disease or at altitude, it causes detrimental increases in pulmonary vascular resistance and pulmonary artery (PA) pressure. The precise intracellular pathways and mechanisms underlying HPV remain unclear, although it is now recognised that both an elevation in smooth muscle intracellular [Ca2+] and a concomitant increase in Ca2+ sensitivity are involved. Several key intracellular protein kinases have been proposed as components of the signal transduction pathways leading to development of HPV, specifically Rho kinase, non-receptor tyrosine kinases (NRTK), p38 mitogen activated protein (MAP) kinase, and protein kinase C (PKC). All of these have been implicated to a greater or lesser extent in pathways leading to Ca2+ sensitisation, and in some cases regulation of intracellular [Ca2+] as well. In this article, we review the role of these key protein kinases in the regulation of vascular smooth muscle (VSM) constriction, applying what is known in the systemic circulation to the pulmonary circulation and HPV. We conclude that the strongest evidence for direct involvement of protein kinases in the mechanisms of HPV concerns a central role for Rho kinase in Ca2+ sensitisation, and a potential role for Src-family kinases in both modulation of Ca2+ entry via capacitative Ca2+ entry (CCE) and activation of Rho kinase, though others are likely to have indirect or modulatory influences. In addition, we speculate that Src family kinases may provide a central interface between the proposed hypoxia-induced generation of reactive oxygen species by mitochondria and both the elevation in intracellular [Ca2+] and Rho kinase mediated Ca2+ sensitisation.

Cellular mechanisms of thromboxane A2-mediated contraction in pulmonary veins

Our objectives were to identify the relative contributions of [Ca2+]i and myofilament Ca2+ sensitivity in the pulmonary venous smooth muscle (PVSM) contractile response to the thromboxane A2 mimetic U-46619 and to assess the roles of PKC, tyrosine kinases (TK), and Rho-kinase (ROK) in that response. We tested the hypothesis that U-46619-induced contraction in PVSM is mediated by both increases in [Ca2+]i and myofilament Ca2+ sensitivity and that the PKC, TK, and ROK signaling pathways are involved. Isometric tension was measured in isolated endothelium-denuded (E-) canine pulmonary venous (PV) rings. In addition, [Ca2+]i and tension were simultaneously measured in fura-2-loaded E- PVSM strips. U-46619 (0.1 nM-1 microM) caused dose-dependent (P < 0.001) contraction in PV rings. U-46619 contraction was attenuated by inhibitors of L-type voltage-operated Ca2+ channels (nifedipine, P < 0.001), inositol 1,4,5-trisphosphate-mediated Ca2+ release (2-aminoethoxydiphenylborate, P < 0.001), PKC (bisindolylmaleimide I, P < 0.001), TK (tyrphostin A-47, P = 0.014), and ROK (Y-27632, P = 0.008). In PV strips, U-46619 contraction was associated with increases in [Ca2+]i and myofilament Ca2+ sensitivity. Both Ca2+ influx and release mediated the early transient increase in [Ca2+]i, whereas the late sustained increase in [Ca2+]i only involved Ca2+ influx. Inhibition of both PKC and ROK (P = 0.006 and P = 0.002, respectively), but not TK, attenuated the U-46619-induced increase in myofilament Ca2+ sensitivity. These results suggest that U-46619 contraction is mediated by Ca2+ influx, Ca2+ release, and increased myofilament Ca2+ sensitivity. The PKC, TK, and ROK signaling pathways are involved in U-46619 contraction.

Differential action of a protein tyrosine kinase inhibitor, genistein, on the positive inotropic effect of endothelin-1 and norepinephrine in canine ventricular myocardium

Experiments were carried out in isolated canine ventricular trabeculae and acetoxymethylester of indo-1-loaded single myocytes to elucidate the role of protein tyrosine kinase (PTK) in the inotropic effect of endothelin-1 (ET-1) induced by crosstalk with norepinephrine (NE). The PTK inhibitor genistein was used as a pharmacological tool. Genistein but not daidzein inhibited the positive inotropic effect and the increase in Ca(2+) transients induced by ET-1 by crosstalk with NE at low concentrations. Genistein and daidzein antagonized the negative inotropic effect and the decrease in Ca(2+) transients induced by ET-1 by crosstalk with NE at high concentrations, but genistein did not affect the antiadrenergic effect of carbachol. Genistein but not daidzein enhanced the positive inotropic effect and the increase in Ca(2+) transients induced by NE via beta-adrenoceptors, while the enhancing effect of genistein was abolished by the protein tyrosine phosphatase inhibitor vanadate. These findings indicate that genistein (1) induces a positive inotropic effect in association with an increase in Ca(2+) transients, (2) inhibits the positive inotropic effect of ET-1 induced by crosstalk with NE, and (3) enhances the positive inotropic effect of NE induced via beta-adrenoceptors by inhibition of PTK. In addition, genistein inhibits the negative inotropic effect of ET-1 induced by crosstalk with NE through a PTK-unrelated mechanism. PTK may play a crucial role in the receptor-mediated regulation of cardiac contractile function in canine ventricular myocardium.

Role of the actin cytoskeleton in G-protein-coupled receptor activation of PYK2 and paxillin in vascular smooth muscle

Dynamic remodeling of the actin cytoskeleton occurs during agonist-induced smooth muscle contraction. Tyrosine phosphorylation of the adaptor protein paxillin has been implicated in regulation of actin filament formation and force development. We have investigated the role of the actin cytoskeleton in noradrenaline (NA)-induced and endothelin (ET)-induced activation of the calcium-dependent nonreceptor tyrosine kinase PYK2 and subsequent phosphorylation of paxillin in rat small mesenteric arteries. NA and ET induced a rapid and prolonged activation of PYK2, as shown by increased phosphorylation at Y402 and Y881, and a concomitant association of the kinase with a Triton X-100 insoluble membrane (cytoskeleton) compartment. Both agonists also increased phosphorylation of paxillin at Y31 and Y118 with a similar time course as PYK2 phosphorylation, and induced its association with the same membrane compartment as PYK2. Treatment of arteries with cytochalasin D disrupted stress fibers and inhibited NA-induced and ET-induced force in a myosin light chain 20 phosphorylation independent and reversible manner. However, cytochalasin D treatment had no effect on NA-induced and ET-induced phosphorylation of either PYK2 or paxillin but did prevent their association with the TritonX-100 insoluble membrane compartment. These results show that in mesenteric arteries an intact cytoskeleton and force development are not prerequisites for G-protein--coupled receptor--induced activation of PYK2 and paxillin, by tyrosine phosphorylation, in vascular tissue, but are necessary for the translocation of PYK2 and paxillin to the membrane.

Acidosis-induced protein tyrosine phosphorylation depends on Ca2+ influx via voltage-dependent Ca2+ channels in SHR aorta

The contractile response to acidosis in isolated aorta from spontaneously hypertensive rat (SHR) depends upon tyrosine phosphorylation of phosphatidylinositol 3 kinase (PI3-kinase) and Ca2+ influx via voltage-dependent Ca2+ channels (VDCC). In this study, verapamil, a VDCC inhibitor, was shown to markedly inhibit acidic pH-induced contraction, whereas the residual contraction in the presence of verapamil was unaffected by the PI3-kinase inhibitor, 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one hydrochloride (LY-294002). Interestingly, the LY-294002-insensitive component of contraction was further inhibited by verapamil in the presence of LY-294002. Western blotting revealed that acidosis stimulated tyrosine phosphorylation of p85, which was abolished when tissues were pretreated with tyrphostin 23, a tyrosine kinase inhibitor, verapamil or EGTA. In fura-2-loaded aortic strips, acidosis induced a rise in intracellular Ca2+ ([Ca2+]i) that was partially inhibited by LY-294002. The residual increase in [Ca2+]i caused by acidosis in the presence of LY-294002 was abolished by verapamil. These findings suggest that acidosis-induced Ca2+ influx through VDCC is the upstream event leading to the tyrosine phosphorylation of PI3-kinase, which in turn contributes to the enhancement of Ca2+ entry to some extent in SHR aorta.

p38 Mitogen-activated protein kinase regulates vasoconstriction in spontaneously hypertensive rats

We investigated whether p42/p44 mitogen-activated protein kinase (MAPK) and/or p38 MAPK participates in the regulation of vascular smooth muscle contraction by endothelin-1 (ET-1) in Wistar-Kyoto rat (WKY) and spontaneously hypertensive rat (SHR). ET-1 (10 nM) induced a sustained contraction in WKY and SHR aortas. PD98059 (100 microM), an inhibitor of p42/p44 MAPK kinase, partially attenuated the ET-1-induced contraction in WKY and SHR. However, SB203580 (10 microM), an inhibitor of p38 MAPK, relaxed the ET-1-induced contraction to the resting levels in SHR, but not in WKY. ET-1 (10 nM) increased phosphorylation of both p42/p44 MAPK and p38 MAPK in WKY and SHR. However, in SHR, p38 MAPK phosphorylation in response to ET-1 stimulation was increased more than in WKY. PD98059 (100 microM) and SB203580 (10 microM) abolished the phosphorylation of p42/p44 MAPK and p38 MAPK in response to ET-1 stimulation in WKY and SHR, respectively. On the other hand, SB203580 (10 microM) did not affect myosin light chain (MLC) phosphorylation in response to ET-1 (10 nM) stimulation in WKY and SHR. From these results, it is concluded that p42/p44 MAPK and/or p38 MAPK partially regulates the ET-1-induced vasoconstriction in WKY. However, p38 MAPK, rather than p42/p44 MAPK, activation plays an important role for the maintenance of ET-1-induced vasoconstriction in SHR through a MLC phosphorylation-independent pathway.

Evidence for a functional calcium-sensing receptor that modulates myogenic tone in rat subcutaneous small arteries

Myogenic tone of small arteries is dependent on the presence of extracellular calcium (Ca(o)(2+)), and, recently, a receptor that senses changes in Ca(2+), the calcium-sensing receptor (CaR), has been detected in vascular tissue. We investigated whether the CaR is involved in the regulation of myogenic tone in rat subcutaneous small arteries. Immunoblot analysis using a monoclonal antibody against the CaR demonstrated its presence in rat subcutaneous arteries. To determine whether the CaR was functionally active, segments of artery (< 250 microm internal diameter) mounted in a pressure myograph with an intraluminal pressure of 70 mmHg were studied after the development of myogenic tone. Increasing Ca(o)(2+) concentration ([Ca(2+)](o)) cumulatively from 0.5 to 10 mM induced an initial constriction (0.5-2 mM) followed by dilation (42 +/- 5% loss of tone). The dose-dependent dilation was mimicked by other known CaR agonists including magnesium (1-10 mM) and the aminoglycosides neomycin (0.003-10 mM) and kanamycin (0.003-3 mM). PKC activation with the phorbol ester phorbol-12,13-dibutyrate (20nM) inhibited the dilation induced by high [Ca(2+)](o) or neomycin, whereas inhibition of PKC with GF109203X (10 microM) increased the responses to Ca(o)(2+) or neomycin, consistent with the role of PKC as a negative regulator of the CaR. We conclude that rat subcutaneous arteries express a functionally active CaR that may be involved in the modulation of myogenic tone and hence the regulation of peripheral vascular resistance.

Rho/Rho kinase signaling mediates increased basal pulmonary vascular tone in chronically hypoxic rats

Recent evidence suggests that Rho/Rho kinase signaling plays an important role in the sustained vasoconstriction induced by many agonists and is involved in the pathogenesis of systemic vascular diseases. However, little is known about its role in increased vascular tone in hypoxic pulmonary hypertension (PH). The purpose of this study was to examine whether Rho/Rho kinase-mediated Ca2+ sensitization contributed to sustained vasoconstriction and increased vasoreactivity in hypoxic PH in rats. Acute intravenous administration of Y-27632, a Rho kinase inhibitor, nearly normalized the high pulmonary arterial blood pressure and total pulmonary resistance in chronically hypoxic rats. In contrast to nifedipine, Y-27632 also markedly decreased elevated basal vascular tone in hypertensive blood-perfused lungs and isolated pulmonary arteries. Y-27632 and another Rho kinase inhibitor, HA-1077, completely reversed nitro-L-arginine-induced vasoconstriction in physiological salt solution-perfused hypertensive lungs, whereas inhibitors of myosin light chain kinase (ML-9), protein kinase C (GF-109203X), phosphatidylinositol 3-kinase (LY-294002), and tyrosine kinase (tyrphostin A23) caused only partial or no reversal of the vasoconstriction. Vasoconstrictor responses to KCl were augmented in hypertensive physiological salt solution-perfused lungs and pulmonary arteries, and the augmentation was eliminated by Y-27632. These results suggest that Rho/Rho kinase-mediated Ca2+ sensitization plays a central role in mediating sustained vasoconstriction and increased vasoreactivity in hypoxic PH.

ET-1 activates Ca2+ sparks in PASMC: local Ca2+ signaling between inositol trisphosphate and ryanodine receptors

Ca+ sparks originating from ryanodine receptors (RyRs) are known to cause membrane hyperpolarization and vasorelaxation in systemic arterial myocytes. By contrast, we have found that Ca2+ sparks of pulmonary arterial smooth muscle cells (PASMCs) are associated with membrane depolarization and activated by endothelin-1 (ET-1), a potent vasoconstrictor that mediates/modulates acute and chronic hypoxic pulmonary vasoconstriction. In this study, we characterized the effects of ET-1 on the physical properties of Ca2+ sparks and probed the signal transduction mechanism for spark activation in rat intralobar PASMCs. Application of ET-1 at 0.1-10 nM caused concentration-dependent increases in frequency, duration, and amplitude of Ca2+ sparks. The ET-1-induced increase in spark frequency was inhibited by BQ-123, an ETA-receptor antagonist; by U-73122, a PLC inhibitor; and by xestospongin C and 2-aminoethyl diphenylborate, antagonists of inositol trisphosphate (IP3) receptors (IP3Rs). However, it was unrelated to sarcoplasmic reticulum Ca2+ content, activation of L-type Ca2+ channels, PKC, or cADP ribose. Photorelease of caged-IP3 indicated that Ca2+ release from IP3R could cross-activate RyRs to generate Ca2+ sparks. Immunocytochemistry showed that the distributions of IP3Rs and RyRs were similar in PASMCs. Moreover, inhibition of Ca2+ sparks with ryanodine caused a significant rightward shift in the ET-1 concentration-tension relationship in pulmonary arteries. These results suggest that ET-1 activation of Ca2+ sparks is mediated via the ETA receptor-PLC-IP3 pathway and local Ca2+ cross-signaling between IP3Rs and RyRs; in addition, this novel signaling mechanism contributes significantly to the ET-1-induced vasoconstriction in pulmonary arteries.

Delayed arteriolar relaxation after prolonged agonist exposure: functional remodeling involving tyrosine phosphorylation

Although arteriolar contraction is dependent on Ca2+-induced myosin phosphorylation, other mechanisms including Ca2+ sensitization and time-dependent phenomena such as cytoskeletal and cellular reorganization may contribute to contractile events. We hypothesized that if arteriolar smooth muscle exhibits time-dependent behavior this may be manifested in differences in relaxation after short- and long-term exposure to contractile agonists. Studies were conducted in isolated arterioles pressurized to 70 mmHg. In initial experiments (n = 10), rate of relaxation was measured after acute (5 min) or prolonged (4 h) exposure to 5 microM norepinephrine (NE). Prolonged exposure to NE resulted in significantly (P < 0.05) increased time for relaxation in physiological salt solution. Rapid relaxation of vessels exposed to NE for 4 h was observed after superfusion with 0 mM Ca2+ buffer, indicating that the alteration in relaxation was reversible and Ca2+ dependent. A similarly impaired dilation was not observed with 4-h exposure to KCl (75 mM). To determine mechanisms contributing to the effects of prolonged NE exposure, studies were performed in the presence of the microtubule depolymerizing agent demecolcine (10 microM) or a series of tyrosine phosphorylation inhibitors. Although demecolcine caused significant vasoconstriction (P < 0.05) and potentiated NE vasoconstriction, it did not prevent the effect of long-term NE exposure on relaxation. Genistein, although having no effect on acute NE-induced contraction, concentration-dependently inhibited prolonged NE constriction. Similarly, Src (PP1) and p42/44 MAP kinase (PD-98059) inhibitors prevented maintenance of long-term NE contraction. The data indicate that prolonged exposure to NE induces biochemical alterations that impair relaxation after removal of the agonist. The contractile effects are Ca2+ dependent and involve tyrosine phosphorylation but do not appear to involve the polymerization state of the microtubule network.

Mitogen-activated protein kinases partially regulate endothelin-1-induced contractions through a myosin light chain phosphorylation-independent pathway

Endothelin (ET), derived from the endothelium of blood vessels, is a potent vasoactive peptide. Although it has been reported to be involved in cardiovascular diseases, such as hypertension, the mechanism by which ET evokes vasoconstriction is still unclear. On the other hand, p42/p44 mitogen-activated protein kinase (MAPK) and p38 MAPK are activated by a variety of growth factors and cellular stresses, respectively. However, the role of p42/p44 MAPK and p38 MAPK on the ET-1-induced vasoconstriction is not fully understood. This study was undertaken to determine whether p42/p44 MAPK and p38 MAPK participate in the regulation of vascular smooth muscle contraction by ET-1. The isometric vasoconstriction and intracellular Ca(2+) ([Ca(2+)](i)) were simultaneously measured using CAF-100. Phosphorylation of myosin light chain (MLC) and p42/p44 MAPK, p38 MAPK were determined by Western blots. In rat thoracic aorta, ET-1 induced a sustained contraction. In contrast, [Ca(2+)](i) was decreased with time. Both PD98059, an inhibitor of p42/p44 MAPK, and SB203580, an inhibitor of p38 MAPK, partially attenuated ET-1-induced contractions in concentration-dependent manners. ET-1 increased phosphorylation of both p42/p44 MAPK and p38 MAPK, and PD98059 and SB203580 completely decreased phosphorylation of p42/p44 MAPK and p38 MAPK in response to ET-1 stimulation, respectively. On the other hand, PD98059 and SB203580 did not affect MLC phosphorylation in response to ET-1 stimulation. These results indicate that p38 MAPK, as well as p42/p44 MAPK, may partially regulate the ET-1-induced contraction through a MLC phosphorylation-independent pathway.

The signal transduction of endothelin-1-induced circular smooth muscle cell contraction in cat esophagus

It has been known that endothelin-1 (ET-1) exerts important actions in gastrointestinal smooth muscle motility, but its precise mechanism remains unsolved. We investigated the intracellular mechanism of ET-1-induced circular smooth muscle cell contraction in cat esophagus. ET-1 produced contraction of smooth muscle cells isolated by enzymatic digestion. The contraction in response to ET-1 was concentration-dependent. Pertussis toxin (PTX) blocked contraction induced by ET-1 in intact cells. To identify the specific G protein involved in the contraction, muscle cells were permeabilized with saponin. The G(i3) or G(beta) protein antibody inhibited the contraction. Neomycin phospholipase C (PLC) inhibitor inhibited the contraction, but 7,7-dimethyleicosadienoic acid (phospholipase A(2) inhibitor) and p-chloromercuribenzoic acid (phospholipase D inhibitor) had no effects. Incubation of permeabilized cells with PLC-beta(3) isozyme antibody inhibited the contraction. 1-(5-Isoquinolinesulfonyl)-2-methylpiperazine, chelerythrine [protein kinase C (PKC) inhibitor], or genistein (protein tyrosine kinase inhibitor) inhibited the contraction, but not by diacylglycerol (DAG) kinase inhibitor, R59949. To test whether the contraction may be PKC isozyme-specific, we examined the effect of PKC isozymes antibodies on the contraction. PKC-epsilon antibody inhibited the contraction. To characterize further the specific PKC isozymes that mediate the contraction, we used, as an inhibitor, N-myristoylated peptides (myr-PKC) derived from the pseudosubstrate sequences of PKC-alphabetagamma, -alpha, -delta, or -epsilon. myr-PKC-epsilon inhibited the contraction, confirming that PKC-epsilon isozyme is involved in the contraction. To examine whether mitogen-activated protein kinases (MAPKs) mediate the contraction, specific MAPK inhibitors [MAPK kinase inhibitor, PD98059, (2'-amino-3'-methoxy-flavone), and p38 MAPK inhibitor, SB202190 (4-4-fluorophenyl) 2-(4-hydroxyphenyl)-5-(4-pyridyl)1H-imidazole)] were used. PD98059 or SB202190 blocked the contraction. ET-1 increased the intensity of the detection bands identified by immunological methods as MAPK monoclonal p44/p42 peptides. PD98059 decreased the intensity of the detection bands compared with ET-1. In conclusion, ET-1-induced contraction in cat esophageal circular muscle cells depends on PTX-sensitive G(i3) protein and PLC-beta(3) isozyme, resulting in the activation of PKC-epsilon- or protein-tyrosine kinase-dependent pathway, subsequently mediating the activation of p44/p42 MAPK or p38 MAPK pathway.

Mechanism of RhoA/Rho kinase activation in endothelin-1- induced contraction in rabbit basilar artery

This study was undertaken to demonstrate the role of the RhoA/Rho kinase pathway in endothelin-1 (ET-1)-induced contraction of the rabbit basilar artery. Isometric tension and Western blot were used to examine ET-1-induced contraction and RhoA activation. The upstream effect on ET-1-induced RhoA activity was determined by using ET(A) and ET(B) receptor antagonists, protein kinase C (PKC), tyrosine kinase, and phosphatidylinositol-3 kinase inhibitors. The downstream effect of ET-1-induced contraction and RhoA activity was studied in the presence of the Rho kinase inhibitor Y-27632. The effect of Rho kinase inhibitor on ET-1-induced myosin light chain (MLC) phosphorylation was investigated by using urea-glycerol-PAGE immunoblotting. We found 1) ET-1 increased RhoA activity (membrane binding RhoA) in a concentration-dependent manner; 2) ET(A), but not ET(B), receptor antagonist abolished the effect of ET-1 on RhoA activation; 3) phosphodylinositol-3 kinase inhibitor, but not PKC and tyrosine kinase inhibitors, reduced ET-1-induced RhoA activation; 4) Rho kinase inhibitor Y-27632 (10 microM) inhibited ET-1-induced contraction; and 5) ET-1 increased the level of MLC phosphorylation. Rho kinase inhibitor Y-27632 reduced the effect of ET-1 on MLC phosphorylation. This study demonstrated that RhoA/Rho kinase activation is involved in ET-1-induced contraction in the rabbit basilar artery. Phosphodylinositol-3 kinase and MLC might be the upstream and downstream factors of RhoA activation.

Tyrosine kinase inhibition attenuates vasopressin-induced contraction of mesenteric resistance arteries: alterations in spontaneously hypertensive rats

This study examined the role of tyrosine kinase-dependent signaling pathways in arginine vasopressin (AVP)-induced contractile responses in resistance arteries from spontaneously hypertensive rats (SHR). Systolic blood pressure was measured in conscious 6- and 21-week old SHR and Wistar Kyoto rats (WKY) by tail cuff measurements. Segments of third-order mesenteric arteries (about 200 microm in diameter, 2mm in length) were mounted in a pressurized chamber with the intraluminal pressure maintained at 45 mmHg. Contractile effects of AVP (10-12 to 10-7 mol/l) were determined in the absence and presence of the selective tyrosine kinase inhibitor tyrphostin A23 (10-5 mol/l) and the inactive analogue, tyrphostin A1 (10-5 mol/l). Systolic blood pressure was significantly higher in SHR compared with age-matched WKY (p < 0.01). AVP increased contraction in a dose-dependent manner with significantly greater responses in adult SHR (pD2 = 10.3 +/- 0.06) than age-matched WKY (pD2 = 9.4 +/- 0.04). Tyrphostin A23 shifted the AVP dose response curve to the right in 6- and 21-week WKY and 6-week SHR, but had little effect on AVP-induced responses in 21-week-old SHR. Tyrphostin A1 did not influence contraction in any groups. Protein tyrosine phosphorylation in VSMCs and mesenteric arteries was increased 2-3 fold in 21-week SHR compared with WKY counterparts. AVP significantly increased tyrosine phosphorylation in VSMCs, with enhanced effects in SHR compared with WKY (p < 0.05). These effects were inhibited by tyrphostin A23. Our findings demonstrate that protein tyrosine kinases contribute to AVP-induced contraction of resistance arteries from WKY and SHR during the phase of developing hypertension. These processes do not seem to play an important role in AVP-induced hypercontractility in SHR with established hypertension.

Involvement of p44/42 mitogen-activated protein kinases in regulating angiotensin II- and endothelin-1-induced contraction of rat thoracic aorta

In order to elucidate the signal transduction pathway of vascular smooth muscle contraction induced by the activation of receptors for angiotensin II and endothelin-1, we examined whether tyrosine kinases and mitogen-activated protein (MAP) kinases are involved in the development of force of contraction in the rat aorta. Isolated aortic smooth muscles without endothelium were incubated in a modified Krebs-Henseleit solution and stimulated with angiotensin II (100 nM) or endothelin-1 (10 nM). A tyrosine kinase inhibitor genistein (10 microM) reduced the angiotensin II- and endothelin-1-induced aortic contraction, while 10 microM of daidzein (an inactive analogue of genistein) did not. The K(+) depolarization-induced contraction was not attenuated by 10 microM of genistein. Selective inhibitors of MAP kinase/extracellular signal-regulated kinase (Erk) kinase (MEK) such as PD98059 [2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one] and U0126 [1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene] inhibited the angiotensin II- and endothelin-1-induced vasocontraction. The p44/42 MAP kinases were phosphorylated in cultured aortic smooth muscle cells and in physiologically contracted aortic vessels stimulated with angiotensin II and endothelin-1 for 5 min. The angiotensin II- and endothelin-1-induced phosphorylations of p44/42 MAP kinases were inhibited by PD98059 as well as U0126 in the intact aorta. These results suggest that the activation of genistein-sensitive tyrosine kinases and p44/42 MAP kinases is involved in the angiotensin II- and endothelin-1-induced rat aortic contraction.

Mechanisms underlying pervanadate-induced contraction of rat cremaster muscle arterioles

The current study examined the role of extracellular Ca2+, calmodulin and myosin light-chain kinase (MLCK) in pervanadate-induced constriction of cannulated, pressurized rat cremaster arterioles. Pervanadate (0.03-100 microM) induced a concentration-dependent constriction of arterioles that was significantly attenuated (P<0.05) by the tyrosine kinase inhibitor tyrphostin 47 (30 microM). The L-type voltage-sensitive Ca2+ channel antagonists verapamil (10 microM) and nifedipine (1 microM) dilated vessels possessing myogenic tone but had no demonstrable effect on pervanadate constriction, while a higher concentration of nifedipine (10 microM) reduced constriction by approximately 50%. Pervanadate-induced contractions were reduced by the calmodulin inhibitor W-7 (N-(6-aminohexyl)-chloro-1-naphtalene sulphonamide, 50 microM) and the MLCK inhibitor ML-7 (1-(5-iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine, 10 or 30 microM). Removal of extracellular Ca2+ abolished the contractile effect of pervanadate. Measurement of changes in arteriolar wall [Ca2+] using the Ca2+ sensitive dye Fura-2 showed that pervanadate did not increase [Ca2+] during arteriolar constriction. These observations suggest that pervanadate-induced contraction of smooth muscle in the cremaster arteriole involves Ca2+/calmodulin-dependent myosin phosphorylation and possibly sensitization of the contractile apparatus to Ca2+.

Bradykinin stimulates ceramide production by activating specific BK-B(1) receptor in rat small artery

Bradykinin (BK), a proinflammatory factor and vasodilator, causes functional change of the small artery. However, it is not clear whether any of these changes induced by BK are mediated by N-acetyl-D-sphingosine (ceramide). Therefore, we investigated whether BK affects the hydrolysis of sphingomyelin and generation of ceramide in the intact rat small artery. Our results suggest that BK induces sphingomyelin hydrolysis and increases ceramide production in a time- and dose-dependent manner. Relative to controls, BK causes a 50% decrease in sphingomyelin levels. Ceramide levels increase in response to BK with the highest level being obtained with 10(-8) M BK as well as similar amounts of ceramide are generated when exogenous sphingomyelinase (SMase) is added. We then determined which of the two BK receptors (BK-B(1) antagonist Lys-Des-Arg(9)-Leu(8)-BK or the BK-B(2) antagonist HOE-140) are implicated in the BK-induced generation of ceramide. The BK-B(2) antagonist did not alter the effect of BK on ceramide generation, whereas the BK-B(1) antagonist blocked the BK-induced production of ceramide. Although ceramide had no effect on KCl-induced constrictions, ceramide dilated preconstricted (phenylephrine) small pressurized rat mesenteric arteries by approximately 40%. These results suggest that the activation of the BK-B(1) receptor mediates the BK-induced activation of SMase and of the production of ceramide. In conclusion, BK-mediated effects on vascular tone may be due, at least in part, to the increased production of ceramide.

Activation of p38 mitogen-activated protein kinases by endothelin and noradrenaline in small arteries, regulation by calcium influx and tyrosine kinases, and their role in contraction

Small-artery responses to vasoconstrictor agonists are important for vascular function. To investigate the signaling pathways involved in contraction, we studied the activation and regulation of p38 mitogen-activated protein kinases (p38MAPKs) and heat shock protein (HSP) kinase by endothelin and noradrenaline in rat mesenteric arteries. Both vasoconstrictors activated p38alpha and/or p38beta but not p38gamma or p38delta, leading to increased HSP kinase activity. p38MAPK activation by noradrenaline was maximum between 2 and 10 minutes and was wholly dependent on calcium influx but insensitive to the tyrosine kinase inhibitor herbimycin A. In contrast, endothelin induced a biphasic response, with activation at 2 and 10 minutes. The early activity was wholly dependent on calcium influx and inhibited by herbimycin A. The later activity was only 50% calcium dependent, was insensitive to herbimycin A, but was 50% inhibited by genistein, a nonselective tyrosine kinase inhibitor. With both agonists, p38MAPK activity returned to basal by 30 minutes. SB203580, a p38MAPK inhibitor, blocked agonist-induced HSP kinase activity, and herbimycin A inhibited activation by endothelin but not by noradrenaline. In addition, SB203580 inhibited noradrenaline-induced contraction but had little effect on contraction to endothelin. These data show that vasoconstrictors use different upstream activators of p38MAPK in vascular tissue and that the p38MAPK pathway is selectively implicated in the contractile response to noradrenaline in small arteries.

Leukotriene D(4)-induced Rho-mediated actin reorganization in human bronchial smooth muscle cells

We investigated the role of cysteinyl leukotriene (CysLT) receptors on leukotriene D(4)-induced actin reorganization and the signaling pathways of the response in human bronchial smooth muscle cells. The effects of leukotriene D(4) on actin reorganization in human bronchial smooth muscle cells were evaluated by dual-fluorescence labeling of filamentous (F) and monomeric (G) actin with fluorescein isothiocyanate (FITC)-labeled phalloidin and Texas Red-labeled DNase I, respectively. Leukotriene D(4) (100 nM) induced actin reorganization in the presence and absence of extracellular Ca(2+). The CysLT type 1 (CysLT(1)) receptor antagonist ONO 1078 (4-oxo-8(-)[p-(4-phenylbutyloxy) benzoylamino]-2-(tetrazol-5-yl)-4H-1-benzopyran hemihydrate) inhibited leukotriene D(4)-induced actin reorganization. Pretreatment with pertussis toxin, C3 exoenzyme, or tyrosine kinase inhibitors significantly reduced leukotriene D(4)-induced actin reorganization. However, phosphatidylinositol-3-kinase and protein kinase C inhibitors had little effect on these responses. These results suggest that leukotriene D(4)-induced actin reorganization in human bronchial smooth muscle cells is extremely dependent on the CysLT(1) receptor coupled with pertussis toxin-sensitive G protein, Rho GTPases and tyrosine phosphorylation pathways.

Tyrosine kinase involvement in renal arteriolar constrictor responses to angiotensin II

Experiments were performed to test the hypothesis that tyrosine kinase activity contributes to renal arteriolar contractile responses to angiotensin (Ang) II. Rats were subjected to short-term enalaprilat treatment to decrease endogenous Ang II formation before tissue was harvested for experiments with the in vitro blood-perfused juxtamedullary nephron technique. Acute surgical papillectomy was used to avoid the indirect afferent arteriolar effect of Ang II that arises through increased tubuloglomerular feedback sensitivity. Arteriolar lumen diameter responses to 1 and 10 nmol/L Ang II were monitored by videomicroscopic methods before and during treatment with various tyrphostin compounds: 100 micromol/L AG18 (broad-spectrum tyrosine kinase inhibitor), 100 nmol/L AG1478 (selective epidermal growth factor receptor tyrosine kinase inhibitor), or 100 micromol/L AG9 (inactive analog). Baseline afferent arteriolar lumen diameter averaged 23.5+/-1.2 micrometer and was not influenced by any tyrphostin. Ang II (10 nmol/L) decreased afferent diameter by 11.1+/-1.0 micrometer under untreated conditions, a response that was not altered by AG9 but significantly blunted by AG18 (34+/-9% inhibition) or AG1478 (52+/-8% inhibition). AG18 did not suppress afferent arteriolar contractile responses to membrane depolarization (20 to 55 mmol/L K(+ )bath). Efferent arteriolar baseline diameter averaged 24.1+/-0.8 micrometer and was unaltered by AG18 or AG1478; however, efferent diameter responses to 10 nmol/L Ang II were diminished 52+/-10% by AG18 and 51+/-13% by AG1478. These observations indicate that Ang II signaling in renal afferent and efferent arteriolar vascular smooth muscle is either mediated or modulated by tyrosine kinase activity, including that of the epidermal growth factor receptor tyrosine kinase.

Involvement of protein kinase C, tyrosine kinases, and Rho kinase in Ca(2+) handling of human small arteries

The mechanisms of Ca(2+) handling and sensitization were investigated in human small omental arteries exposed to norepinephrine (NE) and to the thromboxane A(2) analog U-46619. Contractions elicited by NE and U-46619 were associated with an increase in intracellular Ca(2+) concentration ([Ca(2+)](i)), an increase in Ca(2+)-independent signaling pathways, or an enhancement of the sensitivity of the myofilaments to Ca(2+). The two latter pathways were abolished by protein kinase C (PKC), tyrosine kinase (TK), and Rho-associated protein kinase (ROK) inhibitors. In Ca(2+)-free medium, both NE and U-46619 elicited an increase in tension that was greatly reduced by PKC inhibitors and abolished by caffeine or ryanodine. After depletion of Ca(2+) stores with NE and U-46619 in Ca(2+)-free medium, addition of CaCl(2) in the continuous presence of the agonists produced increases in [Ca(2+)](i) and contractions that were inhibited by nitrendipine and TK inhibitors but not affected by PKC inhibitors. NE and U-46619 induced tyrosine phosphorylation of a 42- or a 58-kDa protein, respectively. These results indicate that the mechanisms leading to contraction elicited by NE and U-46619 in human small omental arteries are composed of Ca(2+) release from ryanodine-sensitive stores, Ca(2+) influx through nitrendipine-sensitive channels, and Ca(2+) sensitization and/or Ca(2+)-independent pathways. They also show that the TK pathway is involved in the tonic contraction associated with Ca(2+) entry, whereas TK, PKC, and ROK mechanisms regulate Ca(2+)-independent signaling pathways or Ca(2+) sensitization.

Involvement of tyrosine phosphorylation in the positive inotropic effect produced by H(1)-receptors with histamine in guinea-pig left atrium

We investigated the effect of stimulation of H(1)-receptors with histamine on protein tyrosine phosphorylation levels in guinea-pig left atrium and evaluated the influences of tyrosine kinase inhibitors on the positive inotropic effect mediated by H(1)-receptors in this tissue. Histamine induced an increase in tyrosine phosphorylation in four main clusters of proteins with apparent molecular weights of 25, 35, 65 and 150 kDa. Tyrosine phosphorylation of these proteins attained a peak around 2 - 3 min following histamine stimulation and then declined to or below basal levels. Histamine-induced protein tyrosine phosphorylation was antagonized by the H(1)-receptor antagonists mepyramine (1 microM) and chlorpheniramine (1 microM), but not by the H(2)-receptor antagonist cimetidine (10 microM). The positive inotropic effect of histamine was depressed in a concentration-dependent manner by the tyrosine kinase inhibitors tyrphostin A25 (50 to 100 microM) and genistein (10 to 50 microM) but not by the inactive genistein analogue daidzein (50 microM). The positive inotropic effect of isoprenaline was unchanged by tyrphostin A25 and genistein. At a concentration of 1 microM histamine produced a dual-component positive inotropic response composed of an initial increasing phase and a second and late developing, greater positive inotropic phase. Treatment with tyrphostin A25 (100 microM) and genistein (50 microM), but not daidzein (50 microM), significantly attenuated the two components of the inotropic response, although genistein suppressed the initial component more markedly than the late component. We conclude that increased protein tyrosine phosphorylation may play an important role in initiating at least some part of the positive inotropic effect of H(1)-receptor stimulation in guinea-pig left atrium.

Attenuation of pressure-induced myogenic contraction and tyrosine phosphorylation by fasudil, a cerebral vasodilator, in rat cerebral artery

The mechanism by which fasudil inhibits pressure-induced myogenic contraction was studied with regard to tyrosine phosphorylation in rat cerebral artery. Intracellular Ca(2+) concentration ([Ca(2+)](i)) and vessel diameter were simultaneously measured. Total tyrosine phosphorylation level and phosphorylation of tyrosine 419 on pp60(src) required for its full catalytic activity were immunocytochemically detected in situ. Fasudil (1 - 100 microM) partially suppressed the increase in [Ca(2+)](i), and totally attenuated contraction elicited by pressurization from 10 to 60 mmHg. Furthermore, fasudil (100 microM) significantly attenuated tyrosine phosphorylation and the activity of pp60(src) augmented in situ by pressure. Herbimycin A (1 - 100 nM) and genistein (3 - 30 microM), tyrosine kinase inhibitors, effectively attenuated the pressure-induced increase in [Ca(2+)](i), contraction, tyrosine phosphorylation, and activation of pp60(src). Both fasudil and herbimycin A directly inhibited the pp60(src) activity in a cell free system. Orthovanadate (100 microM), a tyrosine phosphatase inhibitor, significantly potentiated the pressure-induced increase in [Ca(2+)](i) and contraction. Nicardipine (100 nM), a Ca(2+) antagonist, completely inhibited pressure-induced increase in [Ca(2+)](i) and contraction, but affected neither tyrosine phosphorylation nor activity of pp60(src) in the pressurized arteries. Arginine-glycine-aspartic acid-serine peptide (1 - 100 microM) concentration-dependently reduced the pressure-induced contraction. In addition to the hitherto reported vasodilatory actions of fasudil, the present results suggest the inhibition by fasudil of pressure-induced tyrosine phosphorylation and pp60(src) activation. The wide spectrum of inhibitory actions of fasudil may contribute to the effective attenuation of the pressure-induced contraction in the cerebral artery.

Agonist-dependent difference in the mechanisms involved in Ca2+ sensitization of smooth muscle of porcine coronary artery

This study was undertaken to explore possible signal-transduction mechanisms involved in the Ca2+-sensitizing effects of carbachol and endothelin-1 (ET-1) by using beta-escin-skinned smooth muscle of porcine coronary artery. Pretreatment with C3 exoenzyme of Clostridium botulinum, which selectively inactivates rho p21 by adenosine diphosphate (ADP) ribosylation, resulted in a significant inhibition of ET-1-induced Ca2+ sensitization, but had no effect on carbachol-induced Ca2+ sensitization. Whereas the protein kinase C (PKC) inhibitors calphostin C and staurosporine did not affect the Ca2+-sensitizing effect of carbachol, the tyrosine kinase inhibitors genistein and tyrphostin 25 greatly but incompletely suppressed it. In contrast, the Ca2+-sensitizing effect of ET-1 was significantly inhibited by either calphostin C or genistein. Although the inhibitory effect of calphostin C on ET-1-induced Ca2+ sensitization was less than that of genistein, the effects of calphostin C and genistein were additive. The genistein-sensitive component of ET-1-induced Ca2+ sensitization appeared to include the C3-sensitive one. However, a substantial enhancement by ET-1 of the Ca2+-induced contraction was observed even in the presence of the two inhibitors. In beta-escin-skinned smooth muscle of rabbit mesenteric artery, ET-1-induced Ca2+ sensitization was marginally affected by C3 pretreatment, calphostin C, and genistein. We conclude that, although PKC activation and rho p21 protein-dependent and -independent tyrosine phosphorylation each plays an important role in an increase in myofilament Ca2+ sensitivity, the contributions of these signaling pathways to Ca2+ sensitization are different depending on receptor agonists and tissues used. Furthermore, these data suggest the existence of an as yet undefined signal-transduction mechanism involved in Ca2+ sensitization caused by receptor agonists.

Differential effects of tyrosine kinase inhibitors on contraction and relaxation of the aortas of normotensive and hypertensive rats

The contribution of tyrosine kinase activity to vasoreactivity in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats was investigated on isolated aortic preparations by the use of two tyrosine kinase inhibitors: methyl-2,5-dihydroxycinnamate (30 microM) and genistein (30 microM). The pretreatment of endothelium denuded aorta with methyl-2,5-dihydroxycinnamate reduced the sensitivity of the rings to noradrenaline to a larger extent in SHR than in WKY. The relaxing effects evoked by methyl-2,5-dihydroxycinnamate and genistein on the sustained contraction induced by endothelin-1 were also more pronounced in SHR denuded rings. Furthermore, in presence of methyl-2,5-dihydroxycinnamate, the endothelium-independent contractile responses to equipotent doses of cyclopiazonic acid were more depressed in SHR than in WKY. In WKY and SHR endothelium-intact aortas contracted with either phenylephrine or endothelin-1, carbachol and cyclopiazonic acid evoked endothelium derived relaxing factor (EDRF)/nitric oxide (NO)-dependent relaxations which were reduced by pretreatment of the rings with methyl-2,5-dihydroxycinnamate or genistein. These inhibitory effects were larger in WKY rings and more important on the cyclopiazonic acid response. In addition, sodium orthovanadate (30 microM) potentiated the noradrenaline-mediated contractions of endothelium-denuded SHR rings and reduced the cyclopiazonic acid-induced relaxation of endothelium-intact WKY rings. The present study suggests a regulatory role for tyrosine kinase in the smooth muscle contraction and the endothelium-dependent relaxation in WKY and SHR aortas and demonstrates the existence of a different relationship in the effect of tyrosine kinase inhibitors on vasoreactivity between SHR and WKY. We propose that an increase in the tyrosine kinase activity in SHR could lead to an enhanced reactivity of Ca2+-linked contractile mechanisms. In addition, our results suggest a link between the loss of tyrosine kinase activity and the altered endothelium-dependent relaxation associated with hypertension.

ET(A) receptors are the primary mediators of myofilament calcium sensitization induced by ET-1 in rat pulmonary artery smooth muscle: a tyrosine kinase independent pathway

We have investigated the possibility that ET-1 can induce an increase in myofilament calcium sensitivity in pulmonary artery smooth muscle. Arterial rings were permeabilized using alpha-toxin (120 microg ml(-1)), in the presence of A23187 (10 microM) to 'knock out' Ca2+ stores, and pre-constricted with pCa 6.8 (buffered with 10 mM EGTA). In the presence of this fixed Ca2+ concentration, 1 microM ET-1 induced a sustained, reversible constriction of 0.15 mN. Pulmonary arterial rings were freeze-clamped at the peak of the induced constriction (time matched). Subsequent densitometric analysis revealed that ET-1 (1 microM) increased the level of phosphorylated myosin light chains by 34% compared to an 11% increase in the presence of pCa 6.8 alone. In contrast to ET-1, the selective ET(B) receptor agonist Sarafotoxin S6C (100 nM) failed to induce a significant constriction. The constriction induced by 1 microM ET-1 was reversibly inhibited when the preparation was preincubated (15 min) with the ETA receptor antagonist BQ 123 (100 microM). The constriction measured 0.13 mN in the absence and 0.07 mN in the presence of 100 microM BQ 123. In contrast, the constriction induced by 1 microM ET-1 measured 0.19 mN in the absence and 0.175 mN following a 15 min pre-incubation with the ET(B) antagonist BQ 788 (100 microM). The constriction induced by 1 microM ET-1 measured 0.14 mN in the presence and 0.13 mN following pre-incubation with the tyrosine kinase inhibitor Tyrphostin A23 (100 microM). We conclude that ET-1 induced an increase in myofilament calcium sensitivity in rat pulmonary arteries via the activation of ET(A) receptors and by a mechanism(s) independent of tyrosine kinase.

Lipid second messengers derived from glycerolipids and sphingolipids, and their role in smooth muscle function

The processes that link activation of an external receptor to the internal mechanisms that elicit a physiological response have been the subject of extensive investigation. It has been established that rather than just being an inert barrier to protect the cell from environmental damage, there are populations of phospholipids located within the plasma membrane that act as a reservoir for signalling molecules and when a receptor binds its appropriate activating ligand a chain of events is initiated which leads to the breakdown of these lipids and the release of second messengers. Such processes are rapid enough for physiological responses to be effected. The purpose of this review is to examine the profile of lipid second messengers derived from glycerophospholipids and sphingolipids. In the former class are included phosphoinositide and phosphatidylcholine and the latter includes sphingomyelin. Hydrolysis of such parent compounds is mediated by phospholipases and the profile of metabolites appears to be agonist specific and modulated by a number of mechanisms including heterotrimeric G-protein subunits, small G-proteins, alterations in intracellular calcium concentration, protein kinase C and tyrosine kinases. The recent interest in sphingolipids, particularly in vascular smooth muscle cells, has been provoked by the observation that ceramide and sphingoid base formation is observed in response to vasoconstrictor hormones.

Role of tyrosine phosphorylation in excitation-contraction coupling in vascular smooth muscle

Increasingly it is recognized that tyrosine phosphorylation plays an important part in the regulation of function in differentiated contractile vascular smooth muscle. Tyrosine kinases and phosphatases are present in large amounts in vascular smooth muscle and have been reported to influence a number of processes crucial to contraction, including ion channel gating, calcium homeostasis and sensitization of the contractile process to [Ca2+]i. This review summarizes current understanding regarding the role of tyrosine phosphorylation in excitation-contraction coupling in blood vessels.

Carbachol-induced actin reorganization involves Gi activation of Rho in human airway smooth muscle cells

To determine whether M2 muscarinic receptors are linked to the monomeric G protein Rho, we studied the effect of carbachol on actin reorganization (stress fiber formation) in cultured human airway smooth muscle cells that expressed mainly M2 muscarinic receptors by dual-fluorescence labeling of filamentous (F) and monomeric (G) actin. F-actin was labeled with FITC-labeled phalloidin, and G-actin was labeled with Texas Red-labeled DNase I. Carbachol stimulation induced stress fiber formation (increased F-actin staining) in the cells and increased the F- to G-actin ratio 3.6 +/- 0.4-fold (mean +/- SE; n = 5 experiments). Preincubation with pertussis toxin, Clostridium C3 exoenzyme, or tyrosine kinase inhibitors reduced the carbachol-induced increase in stress fiber formation and significantly decreased the F- to G-actin ratio, whereas a mitogen-activated protein kinase inhibitor, a phosphatidylinositol 3-kinase inhibitor, and a protein kinase C inhibitor were without effect. This study demonstrates that in cultured human airway smooth muscle cells, muscarinic-receptor activation induces stress fiber formation via a pathway involving a pertussis-sensitive G protein, Rho proteins, and tyrosine phosphorylation.