Increase in tone and intracellular Ca2+ in rabbit isolated ear artery by platelet-derived growth factor

The potential effect of imatinib against hypercholesterolemia induced atherosclerosis, endothelial dysfunction and hepatic injury in rabbits

AIMS

Imatinib is an effective tyrosine kinase inhibitor which has different therapeutic actions. The recent work demonstrated the possible beneficial effects of imatinib on the progression of atherosclerosis, endothelial dysfunction, and hypercholesterolemia-associated liver damage in rabbits.

MAIN METHODS

Animals had been distributed in 4 groups: group 1 (non-treated): animals fed regular diet; group 2 high cholesterol [HC]: animals fed 1% cholesterol supplemented diet for 30 days; group 3 (HC-Imatinib): animals fed 1% cholesterol supplemented diet+imatinib (0.01 g/kg daily, p.o) for 30 days; group 4 (Imatinib): animals fed regular diet with imatinib (0.01 g/kg daily, p.o). After thirty days, tissue samples and blood were isolated to be detected biochemically, histologically, and for in vitro analysis.

KEY FINDINGS

HC exhibited significant elevations in serum lipid parameters, CRP, ALT, AST and ALP. Additionally, HC induced significant increases for aortic and hepatic MDA, aortic NO and hepatic PDGFR-β, while significantly exhibited reductions in aortic and hepatic GSH, SOD and hepatic PPARγ1. Moreover, HC produced impairment in ACh-enhanced aortic relaxation and aortic pathological changes. Histopathological examination of HC-fed rabbits revealed hepatic steatosis compared with non-treated group. Imatinib administration exhibited significant decreases in serum lipid parameters, CRP, ALT, AST and ALP. Additionally, imatinib induced significant decreases for aortic and hepatic MDA, aortic NO and hepatic PDGFR-β, while significantly exhibited elevations in aortic and hepatic GSH, SOD and hepatic PPARγ1 compared with HC animals. Furthermore, imatinib significantly protected against HC produced attenuation in ACh-induced aortic relaxation and pathological changes in aortic and hepatic tissues. Interestingly, imatinib could return serum CRP, ALP, hepatic SOD and PDGFR-β to basal values.

SIGNIFICANCE

The recent observation reports that imatinib could have beneficial effect against atherosclerosis progression, vascular malfunction, and liver damage in high cholesterol diet (HCD)-fed rabbits.

Tyrosine kinase inhibitors relax pulmonary arteries in human and murine precision-cut lung slices

BACKGROUND

Tyrosine kinase inhibitors (TKIs) inhibit the platelet derived growth factor receptor (PDGFR) and gain increasing significance in the therapy of proliferative diseases, e.g. pulmonary arterial hypertension (PAH). Moreover, TKIs relax pulmonary vessels of rats and guinea pigs. So far, it is unknown, whether TKIs exert relaxation in human and murine pulmonary vessels. Thus, we studied the effects of TKIs and the PDGFR-agonist PDGF-BB in precision-cut lung slices (PCLS) from both species.

METHODS

The vascular effects of imatinib (mice/human) or nilotinib (human) were studied in Endothelin-1 (ET-1) pre-constricted pulmonary arteries (PAs) or veins (PVs) by videomicroscopy. Baseline initial vessel area (IVA) was defined as 100%. With regard to TKI-induced relaxation, K⁺-channel activation was studied in human PAs (PCLS) and imatinib/nilotinib-related changes of cAMP and cGMP were analysed in human PAs/PVs (ELISA). Finally, the contractile potency of PDGF-BB was explored in PCLS (mice/human).

RESULTS

Murine PCLS: Imatinib (10 μM) relaxed ET-1-pre-constricted PAs to 167% of IVA. Vice versa, 100 nM PDGF-BB contracted PAs to 60% of IVA and pre-treatment with imatinib or amlodipine prevented PDGF-BB-induced contraction. Murine PVs reacted only slightly to imatinib or PDGF-BB. Human PCLS: 100 μM imatinib or nilotinib relaxed ET-1-pre-constricted PAs to 166% or 145% of IVA, respectively, due to the activation of K_ATP-, BK_Ca²⁺- or K_v-channels. In PVs, imatinib exerted only slight relaxation and nilotinib had no effect. Imatinib and nilotinib increased cAMP in human PAs, but not in PVs. In addition, PDGF-BB contracted human PAs/PVs, which was prevented by imatinib.

CONCLUSIONS

TKIs relax pre-constricted PAs/PVs from both, mice and humans. In human PAs, the activation of K⁺-channels and the generation of cAMP are relevant for TKI-induced relaxation. Vice versa, PDGF-BB contracts PAs/PVs (human/mice) due to PDGFR. In murine PAs, PDGF-BB-induced contraction depends on intracellular calcium. So, PDGFR regulates the tone of PAs/PVs. Since TKIs combine relaxant and antiproliferative effects, they may be promising in therapy of PAH.

PDGF-BB regulates the pulmonary vascular tone: impact of prostaglandins, calcium, MAPK- and PI3K/AKT/mTOR signalling and actin polymerisation in pulmonary veins of guinea pigs

Background

Platelet-derived growth factor (PDGF)-BB and its receptor PDGFR are highly expressed in pulmonary hypertension (PH) and mediate proliferation. Recently, we showed that PDGF-BB contracts pulmonary veins (PVs) and that this contraction is prevented by inhibition of PDGFR-β (imatinib/SU6668). Here, we studied PDGF-BB-induced contraction and downstream-signalling in isolated perfused lungs (IPL) and precision-cut lung slices (PCLS) of guinea pigs (GPs).

Methods

In IPLs, PDGF-BB was perfused after or without pre-treatment with imatinib (perfused/nebulised), the effects on the pulmonary arterial pressure (P_PA), the left atrial pressure (P_LA) and the capillary pressure (P_cap) were studied and the precapillary (R_pre) and postcapillary resistance (R_post) were calculated. Perfusate samples were analysed (ELISA) to detect the PDGF-BB-induced release of prostaglandin metabolites (TXA₂/PGI₂). In PCLS, the contractile effect of PDGF-BB was evaluated in pulmonary arteries (PAs) and PVs. In PVs, PDGF-BB-induced contraction was studied after inhibition of PDGFR-α/β, L-Type Ca²⁺-channels, ROCK/PKC, prostaglandin receptors, MAP2K, p38-MAPK, PI3K-α/γ, AKT/PKB, actin polymerisation, adenyl cyclase and NO. Changes of the vascular tone were measured by videomicroscopy. In PVs, intracellular cAMP was measured by ELISA.

Results

In IPLs, PDGF-BB increased P_PA, P_cap and R_post. In contrast, PDGF-BB had no effect if lungs were pre-treated with imatinib (perfused/nebulised). In PCLS, PDGF-BB significantly contracted PVs/PAs which was blocked by the PDGFR-β antagonist SU6668. In PVs, inhibition of actin polymerisation and inhibition of L-Type Ca²⁺-channels reduced PDGF-BB-induced contraction, whereas inhibition of ROCK/PKC had no effect. Blocking of EP_1/3- and TP-receptors or inhibition of MAP2K-, p38-MAPK-, PI3K-α/γ- and AKT/PKB-signalling prevented PDGF-BB-induced contraction, whereas inhibition of EP₄ only slightly reduced it. Accordingly, PDGF-BB increased TXA₂ in the perfusate, whereas PGI₂ was increased in all groups after 120 min and inhibition of IP-receptors did not enhance PDGF-BB-induced contraction. Moreover, PDGF-BB increased cAMP in PVs and inhibition of adenyl cyclase enhanced PDGF-BB-induced contraction, whereas inhibition of NO-formation only slightly increased it.

Conclusions

PDGF-BB/PDGFR regulates the pulmonary vascular tone by the generation of prostaglandins, the increase of calcium, the activation of MAPK- or PI3K/AKT/mTOR signalling and actin remodelling. More insights in PDGF-BB downstream-signalling may contribute to develop new therapeutics for PH.

Concurrent rho-kinase and tyrosine kinase platelet-derived growth factor inhibition in experimental pulmonary hypertension

BACKGROUND

We hypothesized that inhibition of Rho-kinase by fasudil, together with tyrosine kinase platelet-derived growth factor (PDGF) receptor inhibition by imatinib, results in greater pulmonary arterial hypertension (PAH) improvement.

METHODS

The effects of such regimens were investigated on hemodynamics, right ventricle hypertrophy, PDGF and ROCK in experimental monocrotaline (MCT)-induced pulmonary hypertension. Fourteen days after MCT injection, male rats were treated orally for another 14 days with imatinib, fasudil or their combination.

RESULTS

Concurrent imatinib and fasudil administration reversed an MCT-induced increase in right ventricular pressure more than either drug alone and decreased right ventricle hypertrophy (right ventricle weight to left ventricle plus septum weight ratio) significantly. The simultaneous administration of fasudil and imatinib caused a further decrease in plasma PDGF-BB levels compared to either drug alone.

CONCLUSIONS

Inhibition of Rho-kinase by fasudil in addition to tyrosine kinase PDGF inhibition by imatinib can result in further PAH improvement. Such outcome may result from additional impact of the Rho-kinase inhibitor on the decrease in PDGF-induced effects.

Imatinib is partially effective for the treatment of pulmonary capillary hemangiomatosis

A 43-year-old man presented with dyspnea on exertion. Right heart catheterization demonstrated pulmonary arterial hypertension (PAH). He was treated with bosentan, sildenafil and intravenous epoprostenol. Despite the administration of such intensive therapy, the patient's condition deteriorated to a World Health Organization functional class (WHO-FC) of IV. He participated in a clinical trial of imatinib for PAH. After three months of treatment with imatinib, the chest X-ray and echocardiography findings improved, and the WHO-FC class was III. One year after, however, the PAH worsened again, and the patient died 2.6 years after the first diagnosis. At autopsy, patchy capillary proliferation was observed in the lungs. The definitive diagnosis was pulmonary capillary hemangiomatosis.

Analysis of erectile responses to imatinib in the rat

OBJECTIVE

To investigate the erectile and cardiovascular responses to the tyrosine kinase inhibitor imatinib in the rat.

MATERIALS AND METHODS

The effect of intracavernosal injection of imatinib on the intracavernosal pressure (ICP), ICP/mean arterial pressure (MAP) ratio, area under the curve, and duration of the increase in ICP and the effect of intravenous injection of imatinib on the MAP, cardiac output, and total peripheral resistance were investigated. The effect of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester on the responses to imatinib was investigated.

RESULTS

Intracavernosal injection of imatinib produced significant dose-related increases in the ICP, ICP/MAP ratio, area under the curve, and duration of the increase in ICP and decreases in the MAP. The erectile responses to imatinib were rapid in onset and short in duration. The erectile responses to imatinib were not significantly altered by NG-nitro-L-arginine methyl ester or cavernosal nerve crush injury, and imatinib was significantly less potent than the nitric oxide donor sodium nitroprusside in inducing erection. Intravenous injection of imatinib produced significant dose-related decreases in the MAP without significantly changing the cardiac output, and imatinib was significantly less potent than sodium nitroprusside in decreasing the MAP. Systemic vascular resistance was decreased in a significant dose-related manner, and the vasodilator responses to imatinib were not altered by NG-nitro-L-arginine methyl ester.

CONCLUSION

The present results have indicated that imatinib has significant erectile and systemic vasodilator activity in the rat that is not dependent on nitric oxide release. Another tyrosine kinase inhibitor, nilotinib, also increased the ICP and decreased the MAP in the rat. These data suggest that tyrosine kinases might play a constitutive role in maintaining penile tumescence and the baseline vasoconstrictor tone in the peripheral vascular bed.

Imatinib attenuates monocrotaline pulmonary hypertension and has potent vasodilator activity in pulmonary and systemic vascular beds in the rat

Cardiovascular responses to the tyrosine kinase inhibitor imatinib were investigated in the rat. Intravenous injections of 0.3-30 mg/kg imatinib produced small decreases in pulmonary arterial pressure, larger dose-dependent decreases in systemic arterial pressure, and no change or small increases in cardiac output, suggesting that the systemic vasodilator response is more pronounced under baseline conditions. When pulmonary arterial pressure was increased with U-46619 or N(ω)-nitro-L-arginine methyl ester (L-NAME), intravenous injections of imatinib produced larger dose-dependent decreases in pulmonary arterial pressure. Imatinib attenuated the acute hypoxic pulmonary vasoconstrictor response. Vasodilator responses to imatinib were not inhibited by meclofenamate, glybenclamide, or rolipram, suggesting that cyclooxygenase, ATP-sensitive K(+) (KATP) channels, and cAMP were not involved in mediating the response. In a 21-day prevention study, imatinib treatment (50 mg/kg ip) attenuated the increase in pulmonary arterial pressure, right ventricular hypertrophy, and small vessel remodeling induced by monocrotaline. Imatinib reduced PDGF receptor phosphorylation and PDGF-stimulated thymidine incorporation in rat pulmonary artery smooth muscle cells. These data suggest that the beneficial effect of imatinib in pulmonary hypertension may involve inhibition of PDGF tyrosine kinase receptor-mediated effects on smooth muscle cell proliferation and on vasoconstrictor tone. These results indicate that imatinib has nonselective vasodilator activity in the pulmonary and systemic vascular beds similar to the Rho kinase inhibitor fasudil and the calcium entry antagonist isradipine. The present results are consistent with the hypothesis that imatinib may inhibit a constitutively active tyrosine kinase vasoconstrictor pathway in the pulmonary and systemic vascular beds in the rat.

Tyrosine kinase inhibitors are potent acute pulmonary vasodilators in rats

Tyrosine kinase inhibitors are promising for the treatment of severe pulmonary hypertension. Their therapeutic effects are postulated to be due to inhibition of cell growth-related kinases and attenuation of vascular remodeling. Their potential vasodilatory activities have not been explored. Vasorelaxant effects of the tyrosine kinase inhibitors imatinib, sorafenib, and nilotinib were examined in isolated pulmonary arterial rings from normal and pulmonary hypertensive rats. Phosphorylation of myosin light chain phosphatase and myosin light chain was assessed by Western blots. Acute hemodynamic effects of imatinib were tested in the pulmonary hypertensive rats. In normal pulmonary arteries, imatinib reversed serotonin- and U46619-induced contractions in a concentration-dependent and endothelium-independent manner. Sorafenib and nilotinib relaxed U46619-induced contraction. Imatinib inhibited activation of myosin phosphatase induced by U46619 in normal pulmonary arteries. All three tyrosine kinase inhibitors concentration-dependently and completely reversed the spontaneous contraction of hypertensive pulmonary arterial rings unmasked by inhibition of nitric oxide synthase. Acute intravenous administration of imatinib reduced high right ventricular systolic pressure in pulmonary hypertensive rats, with little effect on left ventricular systolic pressure and cardiac output. We conclude that tyrosine kinase inhibitors have potent pulmonary vasodilatory activity, which could contribute to their long-term beneficial effect against pulmonary hypertension. Vascular smooth muscle relaxation mediated via activation of myosin light chain phosphatase (Ca(2+) desensitization) appears to play a role in the imatinib-induced pulmonary vasodilation.

Spatial association of the Cav1.2 calcium channel with α5β1-integrin

Engagement of α(5)β(1)-integrin by fibronectin (FN) acutely enhances Cav1.2 channel (Ca(L)) current in rat arteriolar smooth muscle and human embryonic kidney cells (HEK293-T) expressing Ca(L). Using coimmunoprecipitation strategies, we show that coassociation of Ca(L) with α(5)- or β(1)-integrin in HEK293-T cells is specific and depends on cell adhesion to FN. In rat arteriolar smooth muscle, coassociations between Ca(L) and α(5)β(1)-integrin and between Ca(L) and phosphorylated c-Src are also revealed and enhanced by FN treatment. Using site-directed mutagenesis of Ca(L) heterologously expressed in HEK293-T cells, we identified two regions of Ca(L) required for these interactions: 1) COOH-terminal residues Ser(1901) and Tyr(2122), known to be phosphorylated by protein kinase A (PKA) and c-Src, respectively; and 2) two proline-rich domains (PRDs) near the middle of the COOH terminus. Immunofluorescence confocal imaging revealed a moderate degree of wild-type Ca(L) colocalization with β(1)-integrin on the plasma membrane. Collectively, our results strongly suggest that 1) upon ligation by FN, Ca(L) associates with α(5)β(1)-integrin in a macromolecular complex including PKA, c-Src, and potentially other protein kinases; 2) phosphorylation of Ca(L) at Y(2122) and/or S(1901) is required for association of Ca(L) with α(5)β(1)-integrin; and 3) c-Src, via binding to PRDs that reside in the II-III linker region and/or the COOH terminus of Ca(L), mediates current potentiation following α(5)β(1)-integrin engagement. These findings provide new evidence for how interactions between α(5)β(1)-integrin and FN can modulate Ca(L) entry and consequently alter the physiological function of multiple types of excitable cells.

Enhanced contractile response of the basilar artery to platelet-derived growth factor in subarachnoid hemorrhage

BACKGROUND AND PURPOSE

The level of platelet-derived growth factor (PDGF) in cerebrospinal fluid is elevated in subarachnoid hemorrhage (SAH). Therefore, the contractile effect of PDGF on the basilar artery was examined in SAH.

METHODS

A rabbit double-hemorrhage SAH model was used. In the medial layers of the control basilar artery, PDGF had no effect on contraction up to 1 nmol/L, whereas 3 nmol/L PDGF induced slight contraction. In SAH, PDGF induced an enhanced contraction with an increase in [Ca(2+)](i) at 1 nmol/L and higher concentrations. The levels of [Ca(2+)](i) and tension induced by 1 nmol/L PDGF in SAH were 17% and 20%, respectively, of those obtained with 118 mmol/L K(+) depolarization. The PDGF-induced elevation of [Ca(2+)](i) and contraction seen in SAH were abolished in the absence of extracellular Ca(2+). In alpha-toxin-permeabilized strips of SAH animals, PDGF induced no further development of tension during contraction induced by 300 nmol/L Ca(2+), suggesting no direct effect on myofilament Ca(2+) sensitivity. Genistein at 10 micromol/L completely inhibited the tension induced by 1 nmol/L PDGF. The level of myosin light-chain phosphorylation was significantly increased by 1 nmol/L PDGF.

CONCLUSIONS

These results show that the contractile response to PDGF of the basilar artery was enhanced in SAH. The PDGF-induced contraction depended mostly on tyrosine phosphorylation and Ca(2+)-dependent myosin light-chain phosphorylation. The enhancement of the responsiveness to PDGF may therefore contribute to the development of cerebral vasospasm after SAH.

Src family tyrosine kinases mediate contraction of rat isolated tail arteries in response to a hyposmotic stimulus

OBJECTIVE

Hypotonic solutions cause vasoconstriction in rat tail arteries, due largely to activation of L-type calcium channels (CaV1.2). We studied possible roles of tyrosine kinases, particularly src family kinases (SFK) and extracellular signal-related kinases (ERK1/2), in this response.

METHODS

Rat tail arteries were mounted on a myograph for measurement of isometric force. Arteries were bathed in isosmotic physiological saline solution (300 mOsm/l) containing 50 mmol/l mannitol and were stimulated by a hyposmotic solution containing 0 mmol/l mannitol (PSS-M). Activation of tyrosine kinases and ERK1/2 by hyposmotic solution was examined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and western blotting on rat tail artery lysates with specific phospho-antibodies.

RESULTS

Western blotting showed SFK src and yes present in rat tail artery. PSS-M increased tyrosine phosphorylation of several proteins, including SFK and ERK1/2. Genistein blocked phosphorylation of SFK and ERK1/2 by PSS-M. In isolated arteries PSS-M caused a contraction inhibited by the tyrosine kinase inhibitor, genistein, and three structurally different selective SFK inhibitors, herbimycin-A, PP1 and SU6656. Mitogen-activated protein kinase kinase inhibitor PD98059 or selective inhibitors of platelet-derived growth factor receptor (AG1296) and epidermal growth factor receptor (AG1478) had no effect on contraction induced by a hypotonic solution.

CONCLUSIONS

Hyposmotic conditions activate SFK, src and yes, and contract rat tail artery by a SFK-dependent mechanism. ERK1/2 are activated by the hypotonic solution, but do not play a role in the contractile response. SFK modulation of CaV1.2 may be an important mechanism mediating vasoconstriction to mechanical stimuli in vascular smooth muscle.

Involvement of Src tyrosine kinase and mitogen-activated protein kinase in the facilitation of calcium channels in rat nucleus of the tractus solitarius by angiotensin II

It is recognized that brain contains all the components of the renin-angiotensin systems (RAS). The nucleus of the tractus solitarius (NTS) is known to play a major role in the regulation of cardiovascular, respiratory, gustatory, hepatic and swallowing functions. Voltage-dependent Ca2+ channels (VDCCs) serve as crucial mediators of membrane excitability and Ca2+-dependent functions such as neurotransmitter release, enzyme activity and gene expression. The purpose of this study was to investigate the effects of angiotensin II (Ang II) on VDCC currents (I(Ca)) in the NTS using patch-clamp recording methods. An application of Ang II caused facilitation of L-type I(Ca) in a concentration-dependent manner with an EC50 of 167 nm and a Hill coefficient of 1.73. AT1 receptor antagonist losartan antagonized the Ang II-induced facilitation of I(Ca). Intracellular dialysis of the Galpha(i)-protein antibody attenuated the Ang II-induced facilitation of I(Ca). Both Src tyrosine kinase inhibitor and mitogen-activated protein kinase (MAPK) inhibitor attenuated the Ang II-induced facilitation of I(Ca). p38 MAPK inhibitor also attenuated the Ang II-induced facilitation of I(Ca). These results indicate that Ang II facilitates L-type VDCCs via Galpha(i)-proteins involving Src tyrosine kinase and p38 MAPK kinase mediated by AT1 receptors in NTS.

PDGF and cardiovascular disease

Platelet-derived growth factor (PDGF) was identified in a search for serum factors that stimulate smooth muscle cell (SMC) proliferation. During the development of lesions of atherosclerosis that can ultimately lead to vessel occlusion, SMC are stimulated by inflammatory factors to migrate from their normal location in the media. They accumulate within the forming lesion where they contribute to lesion expansion by proliferation and deposition of extracellular matrix. Different genetic manipulations in vascular cells combined with various inhibitory strategies have provided strong evidence for PDGF playing a prominent role in the migration of SMC into the neointima following acute injury and in atherosclerosis. Other activities of PDGF identified in vivo suggest additional functions for PDGF in the pathogenesis of cardiovascular disease.

Fenamates stimulate BKCa channel osteoblast-like MG-63 cells activity in the human

BACKGROUND

The fenamates, a family of nonsteroidal anti-inflammatory drugs that are derivatives of N-phenylanthranilic acid, are the inhibitors of cyclo-oxygenase. The ionic mechanism of actions of these compounds in osteoblasts is not well understood.

METHODS

The effects of the fenamates on ionic currents were investigated in a human osteoblast-like cell line (MG-63) with the aid of the whole-cell and inside-out configurations of the patch-clamp technique.

RESULTS

In MG-63 cells, niflumic acid and meclofenamic acid increased K+ outward currents (IK). The niflumic acid-stimulated IK was reversed by subsequent application of iberiotoxin or paxilline, yet not by that of glibenclamide or apamin. In the inside-out configuration, niflumic acid (30 micromol/L) added to the bath did not modify single-channel conductance but increased the activity of large-conductance Ca2+-activated K+ (BKCa) channels. The EC50 values for niflumic acid- and meclofenamic acid-induced channel activity were 22 and 24 micromol/L, respectively. Niflumic acid (30 micromol/L) and meclofenamic acid (30 micromol/L) shifted the activation curve of BKCa channels to less positive membrane potentials. Membrane stretch potentiated niflumic acid-stimulated channel activity. The rank order of potency for the activation of BKCa channels in these cells was niflumic acid = meclofenamic acid > tolfenamic acid > flufenamic acid > nimesulide. Evans blue and nordihydroguaiaretic acid increased channel activity; however, indomethacin, piroxicam, and NS-398 had no effect on it.

CONCLUSIONS

The fenamates can stimulate BKCa channel activity in a manner that seems to be independent of the action of these drugs on the prostaglandin pathway. The activation of the BKCa channel may hyperpolarize the osteoblast, thereby modulating osteoblastic function.

Platelet-derived growth factor receptors expressed in response to injury of differentiated vascular smooth muscle in vitro: effects on Ca2+ and growth signals

Vascular smooth muscle cells (VSMCs) in the intact vascular wall are differentiated for contraction, whereas the response to vascular injury involves transition towards a synthetic phenotype, with increased tendency for proliferation. Platelet-derived growth factor (PDGF) is thought to be important for this process. We investigated expression and functional coupling of PDGF receptors (PDGFRs) alpha and beta in rat tail arterial rings kept in organ culture, in order to capture early events in the phenotypic transition. In freshly dissected rings no PDGFR immunoreactivity was found in medial VSMCs, whereas PDGFR alpha was detected in nerve fibres. After organ culture for 1-4 days PDGFR alpha and beta as well as phospholipase Cgamma2 (PLCgamma2), known to couple to PDGFR, were expressed in VSMCs within 100 microm of the cut ends. Calponin, a marker for the contractile phenotype, was decreased near the injured area, suggesting that cells were in transition towards synthetic phenotype. In these cells, which showed functional Ca2+-release from the sarcoplasmic reticulum, PDGF-AB (100 ng x mL(-1)) had no effect on [Ca2+]i, whereas cultured VSMCs obtained from explants of rat tail arterial rings responded to PDGF-AB with an increase in [Ca2+]i. However, PDGFR within the cultured rings coupled to growth signalling pathways, as PDGF-AB caused a tyrphostin AG1295-sensitive activation of extracellular signal-regulated kinases 1 and 2 and of [3H]-thymidine incorporation. Thus, early expression of PDGFR in VSMC adjacent to sites of vascular injury coincides with signs of dedifferentiation. These receptors couple to growth signalling, but do not activate intracellular Ca2+ release.

Platelet-derived growth factor causes endothelium-independent relaxation of rabbit mesenteric artery via the release of a prostanoid

Recent evidence has indicated that the mitogen platelet-derived growth factor (PDGF) can act acutely to regulate arterial tone. In this study we demonstrate that the BB isoform of PDGF (PDGF-BB) can cause endothelium-independent relaxation of rabbit isolated mesenteric arteries. In endothelium-denuded arteries, PDGF-BB (40 pM - 8.0 nM) caused concentration-dependent relaxation of noradrenaline-induced tone. The relaxation to PDGF-BB was abolished by a cyclo-oxygenase inhibitor, indomethacin (10 microM) and by the PDGF receptor-associated tyrosine kinase inhibitor, tyrphostin AG1295 (50 microM), but not by N:(G)-monomethyl-L-arginine (L-NMMA, 200 microM), an inhibitor of nitric oxide (NO) synthase. PDGF-BB (4.0 nM) significantly increased the release of prostacyclin (PGI(2)) in endothelium-denuded arteries. Exogenously applied iloprost (1 microM), a stable analogue of PGI(2), relaxed the endothelium-denuded artery. PDGF-BB (4.0 nM) significantly increased the cyclic AMP content. In the absence of Ca(2+), PDGF-BB (4.0 nM) failed to relax the artery, and the release of PGI(2) was almost completely suppressed. In addition, the release of PGI(2) by PDGF-BB (4.0 nM) was significantly reduced in the presence of endothelium. The effect of endothelium was eliminated by L-NMMA (200 microM) and PGI(2) release increased. These data indicate that in rabbit mesenteric arteries, PDGF-BB can evoke endothelium-independent relaxation by stimulating the synthesis of PGI(2). The PDGF-BB-induced prostaglandin synthesis is dependent on both Ca(2+) and tyrosine phosphorylation of the PDGF receptor, and is attenuated by endothelium-derived NO.

Effect of mitogens on growth and contractile responses of rat small arteries: In vitro studies

Rat mesenteric and epigastric small arteries were cultured to investigate influences of mitogens on contractility, proliferation and protein synthesis. Wistar rat arteries were cultured in serum-free Dulbecco's Modified Eagle Medium, first, for 24 h to equilibrate and then for a further 24-48 h either in the absence or presence of test substances: angiotensin II (AII), 1 microM; AII, 1 microM + platelet derived growth factor BB-chain (PDGF-BB), 1 ng mL-1; PDGF-BB, 1 ng mL-1; PDGF-BB, 30 ng mL-1. No mechanical stress was applied. Viability was assessed by myography, protein synthesis by 6-h incorporation of 35S-methionine and proliferation by both 48-h 3H-thymidine-incorporation and immunohistochemical analysis using the thymidine analogue 5-bromo-2'-deoxyuridine. After 3 days in culture, the contractile responses of arteries to phenylephrine, serotonin, AII and PDGF-BB were preserved. Stimulation with PDGF-BB (30 ng mL-1) increased protein synthesis 1.5- (mesenteric) and 1. 9-fold (epigastric). Similarly, stimulation with PDGF-BB (30 ng mL-1) increased 3H-thymidine incorporation of unstimulated arteries 3.4- (mesenteric) and 2.8-fold (epigastric). The other treatments affected neither protein synthesis nor proliferation. Immunohistochemical analysis showed that the proliferation was occurring primarily in the adventitia and that the levels of apoptosis were unaltered by culture. The effects of AII and PDGF-BB on remodelling did not correlate with their contractile effects: epigastric arteries responded strongly to AII and PDGF-BB, while mesenteric arteries responded weakly. The results suggest that organ culture conditions which preserve contractile function may not be sufficient to preserve trophic mechanisms.

Effects of protein tyrosine kinase inhibitors on voltage-operated calcium channel currents in vascular smooth muscle cells and pp60(c-src) kinase activity

1. Tyrosine kinases have been proposed as regulators of voltage-operated calcium channels. The effects of a range of structurally different inhibitors of protein tyrosine kinases (PTK) were examined on voltage-operated calcium channel currents (I(Ba)) and pp60(c-src) kinase (c-src) activity in vitro. 2. I(Ba) was measured in single myocytes isolated from rabbit ear artery by conventional whole cell voltage-clamp techniques. The activity of purified human c-src was measured in vitro using a non-radioactive assay. 3. Bath application of tyrphostin-23 and genistein (non-selective PTK inhibitors), bistyrphostin (a receptor-PTK-selective inhibitor) and PP1 (a src family-selective inhibitor) inhibited I(Ba) in a concentration-dependent manner over a range of test membrane potentials. Intracellular application of peptide-A, a peptide inhibitor of c-src also inhibited currents. Inhibitor potency series against I(Ba) was PP1 > genistein > tyrphostin 23 > bistyrphostin. 4. Tyrphostin-23, genistein, PP1, and peptide-A shifted the steady-state inactivation curves in a hyperpolarized direction without altering their slope. The inhibitors had no significant effects on I(Ba) activation calculated from current-voltage relationships. 5. The agents inhibited c-src activity in a concentration-dependent manner. The order of potency was PP1 > genistein > peptide-A > tyrphostin-23 > bistyrphostin. The IC(50) for inhibition of c-src activity was similar to the IC(50) for inhibition of I(Ba) in all cases. 6. Western blot analysis with a specific antibody to c-src showed the presence of this cytoplasmic tyrosine kinase in rabbit ear artery cells. 7. A range of structurally dissimilar inhibitors of PTKs inhibit I(Ba) and c-src activity with similar potency. These data provide further evidence implicating endogenous c-src in the modulation of L-type calcium channels in vascular smooth muscle cells.

Mechanisms through which PDGF alters intracellular calcium levels in U-1242 MG human glioma cells

PDGF-BB induces a rapid, sustained increase in intracellular calcium levels in U-1242 MG cells. We used several calcium channel blockers to identify the types of channels involved. L channel blockers (verapamil, nimodipine, nicardipine, nitrendipine and taicatoxin) had no effect on PDGF-BB induced alterations in intracellular calcium. Blockers of P, Q and N channels (omega-agatoxin-IVA, omega-conotoxin MVIIC and omega-conotoxin GVIA) also had no effect. This indicates that these channels play an insignificant role in supplying the Ca2+ necessary for PDGF stimulated events in U-1242 MG cells. However, a T channel blocker (NDGA) and the non-specific (NS) calcium channel blockers (FFA and SK&F 9365) abolished PDGF-induced increases in intracellular calcium. This indicates that PDGF causes calcium influx through both non-specific cationic channels and T channels. To study the participation of intracellular calcium stores in this process, we used thapsigargin, caffeine and ryanodine, all of which cause depletion of intracellular calcium stores. The PDGF effect was abolished using both thapsigargin and caffeine but not ryanodine. Collectively, these data indicate that in these human glioma cells PDGF-BB induces release of intracellular calcium from caffeine- and thapsigargin-sensitive calcium stores which in turn lead to further calcium influx through both NS and T channels.

Symptomatic vasospasm after resection of a suprasellar pilocytic astrocytoma: case report and possible pathogenesis

BACKGROUND

Cerebral vasospasm from pathology other than subarachnoid hemorrhage is uncommon. A case of severe vasospasm after resection of a suprasellar pilocytic astrocytoma is reported.

METHODS

A 45-year-old male presented with headache, left facial numbness, bilateral visual loss, and ataxia. Evaluation revealed a large suprasellar tumor, which was resected. Pathologic examination showed pilocytic astrocytoma. The patient developed hemiparesis and aphasia on the fifth postoperative day. Vascular spasm was documented on angiography and by transcranial Doppler.

RESULTS

Intraarterial papaverine resulted in moderate angiographic improvement. Attempts to open middle cerebral artery branches with angioplasty were unsuccessful. The patient subsequently developed a left middle cerebral artery infarct.

CONCLUSIONS

To our knowledge, this is the first description of vasospasm after resection of an astrocytoma. Possible mechanisms contributing to this unusual complication after resection of tumors are discussed.

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.

Contrasting effects of platelet-derived growth factor (PDGF) isomers on mitogenesis, contraction and intracellular calcium concentration in human vascular smooth muscle

The present study was aimed at characterizing the responses of human vascular smooth muscle to all three dimeric isomers of platelet-derived growth factor (PDGF-AA, -AB and -BB) in terms of mitogenesis, contraction and intracellular calcium concentration. The potential of interaction between PDGF and endothelin-1 (ET-1) was also investigated. All three PDGF isoforms (0.1-20 ng mL-1) stimulated DNA synthesis in cultured human coronary artery and saphenous vein vascular smooth muscle cells (VSMC), measured by [3H]thymidine incorporation. PDGF-AB and -BB elicited comparable large increases in DNA synthesis of maximum 595 +/- 149% (P = 0.001, n = 9) and 576 +/- 17% (P < 0.001, n = 5), respectively, whereas PDGF-AA was only weakly mitogenic (61 +/- 16% increase; P < 0.05, n = 3). At a threshold concentration, PDGF acted in synergy with ET-1 to enhance DNA synthesis (816 +/- 337% increase; P < 0.05, n = 7). In contrast to mitogenesis, none of the three PDGF isomers had any effect on contraction of human saphenous veins in vitro, nor did they affect the contractile response to ET-1, 5-HT or the thromboxane mimetic U46619. The effects of the three PDGF isomers on intracellular calcium ([Ca2+]i) rises in cultured human VSMC were heterogeneous, with PDGF-BB inducing the largest increase in [Ca2+]i (442 +/- 53 nmol L-1) vs. PDGF-AB (290 +/- 28 nmol L-1), whilst PDGF-AA had no effect. Both the responses to PDGF-AB and-BB relied upon intracellular calcium release, whilst only PDGF-AB showed additional dependence on influx of extracellular calcium. In summary, PDGF is strongly mitogenic and comitogenic with ET-1, despite not being a vasoconstrictor, for human VSMC. Also, human VSMC showed heterogeneous responses to the three PDGF isoforms. These results implicate PDGF, and in particular the PDGF receptor-beta, as important role players in the development of vascular smooth muscle-mediated intimal thickening in humans.

Differential effects of lovastatin on mitogen induced calcium influx in human cultured vascular smooth muscle cells

1. In this study the effect of lovastatin, an inhibitor of cholesterol and isoprenoid synthesis, on the rises in intracellular calcium concentration ([Ca2+]i) induced by platelet derived growth factor BB (PDGF-BB), angiotensin II (AII), low density lipoproteins (LDL) and foetal calf serum (FCS) was examined in human cultured vascular smooth muscle cells (VSMC) from saphenous vein. Changes in [Ca2+]i were measured in cell suspensions by the Ca2+ sensitive probe, fura 2. 2. Incubation with lovastatin for 24-26 h markedly reduced the peak rise and sustained phase of [Ca2+]i elevation in response to PDGF-BB but the responses to AII, LDL and FCS were unaffected. Further experiments showed that lovastatin pretreatment inhibited PDGF-BB induced Ca2+ influx but not intracellular Ca2+ release. This inhibition could be overcome by co-incubation with mevalonic acid. 3. Pretreatment of cells with the heterotrimeric G protein inhibitor pertussis toxin for up to 24 h completely abolished AII-induced [Ca2+]i rises but the response to PDGF-BB was unaffected. 4. The tyrosine kinase inhibitor genistein largely abolished PDGF-BB-induced [Ca2+]i elevation but had no significant effect on AII-induced responses. 5. Pre-incubation with lovastatin had no effect on the level of tyrosine phosphorylation of PDGF-beta receptors (as measured by Western blot) in response to the PDGF-BB ligand. 6. PDGF-BB elicits Ca2+ influx via a tyrosine kinase-dependent mechanism distinct from the heterotrimeric G protein coupled pathway utilized by AII. Lovastatin most likely acts by inhibition of isoprenylation (via blockade of isoprenoid synthesis) of an intermediate molecule involved in PDGF-BB-induced Ca2+ influx.

Interleukin-2 modulates the responsiveness to angiotensin II in cultured vascular smooth muscle cells

Preincubation with interleukin-2 (IL-2), a T cell-derived cytokine, enhanced the increase in intracellular Ca2+ ([Ca2+]i) induced by angiotensin II (AII) in vascular smooth muscle cells (VSMC). IL-2 itself did not affect the basal [Ca2+]i level or the maximal response of [Ca2+]i increase induced by AII. Furthermore, IL-2-induced enhancement was not observed in the absence of extracellular Ca2+, suggesting that IL-2 enhances Ca2+ influx induced by AII. IL-2 also enhanced the stimulation of DNA synthesis induced by AII, although IL-2 alone did not stimulate DNA synthesis. Genistein, an inhibitor of protein tyrosine kinases, significantly inhibited IL-2-induced enhancement of both Ca2+ influx and DNA synthesis induced by AII. A neutralizing antibody against heparin-binding epidermal growth factor-like growth factor (HB-EGF) partially inhibited IL-2-induced enhancement of DNA synthesis induced by AII. These findings suggest that autocrine HB-EGF is partially involved in the mechanism of IL-2-induced enhancement of DNA synthesis. On the other hand IL-2 stimulated both glycosaminoglycan (GAG) and prostacyclin syntheses and enhanced the stimulation of both GAG and prostacyclin syntheses induced by AII. Therefore, IL-2 may play important roles in the pathogenesis of atherosclerosis and vascular disease by modulating the responsiveness to AII in VSMC.

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

1. We have studied the effect of endothelin-1 stimulation on protein tyrosine phosphorylation levels in intact small mesenteric arteries of the rat and investigated the effects of tyrosine kinase inhibition on the contractile response to this agonist. 2. Endothelin-1 stimulated a rapid (20 s), sustained (up to 20 min) and concentration-dependent (1-100 nM) increase in protein tyrosine phosphorylation levels which coincided temporally with the contractile response in intact and alpha-toxin permeabilized small artery preparations. Tyrosine phosphorylation was increased in four main clusters of proteins of apparent molecular mass 28-33, 56-61, 75-85 and 105-115 kDa. Endothelin-1-induced protein tyrosine phosphorylation was independent of extracellular calcium, antagonized by the tyrosine kinase inhibitor tyrphostin A23 but not by the inactive tyrphostin A1. 3. In intact small arteries tyrphostin A23 inhibited the force developed to endothelin-1 at all concentrations studied; at higher concentrations (10 and 100 nM) the profile of contraction was altered from a sustained to a transient response. Tyrphostin A1 inhibited the contractile response to endothelin-1 at all concentrations except 100 nM; the profile of the response was not altered. Neither tyrphostin affected the transient phasic contraction induced by endothelin-1 (100 nM) in the absence of extracellular calcium. 4. In rat alpha-toxin permeabilized mesenteric arteries endothelin-1 caused a concentration-dependent increase in force in the presence of 10 microM GTP and low (pCa 6.7) constant calcium, demonstrating increased sensitivity of the contractile apparatus to calcium. Tyrphostin A23 inhibited this response by approximately 50%, tyrphostin A1 did not affect endothelin-1-induced calcium sensitization of force. 5. We conclude that increased tyrosine phosphorylation is important in the contractile response induced by endothelin-1 in intact small mesenteric arteries. Furthermore our data implicate activation of this signalling pathway in the tonic phase of contraction possibly through modulation of the sensitivity of the contractile apparatus to calcium.

Platelet-derived growth factor (PDGF): actions and mechanisms in vascular smooth muscle

1. PDGF is a highly hydrophilic cationic glycoprotein (M(r) 28-35kDa) produced by platelets, monocyte/macrophages, endothelial cells and vascular smooth muscle cells under some conditions. 2. Since its original description, PDGF has attracted much attention and it is currently believed to play a role in atherosclerosis and other vascular pathologies. 3. This review describes the vascular biology of PDGF. It particularly focuses on recent findings regarding the intracellular signals activated by PDGF in the context of vascular smooth muscle cell proliferation, migration and, contraction.

Tyrosine kinase signaling pathways modulate angiotensin II-induced calcium ([Ca2+]i) transients in vascular smooth muscle cells

Tyrosine kinases have been implicated in vascular smooth muscle cell proliferation and contraction. Underlying mechanisms may involve C(a2+) -dependent pathways. This study assesses relationships between angiotensin II (Ang II)-stimulated phospholipase C-mediated Ca2+ transients and tyrosine kinase-dependent pathways in vascular smooth muscle cells. Intracellular free Ca2+ concentration ([Ca2+]i) was measured in primary cultured unpassaged vascular smooth muscle cells derived from mesenteric resistance vessels of Wistar-Kyoto rats with the use of fura 2 methodology. [Ca2+]i effects of Ang II (1 nmol/L) were determined in vascular smooth muscle cells in which tyrosine kinase pathways were stimulated by insulin (70 muU/mL; 0.5 nmol/L), insulin-like growth factor-I (1 ng/mL; 0.13 nmol/L), or platelet-derived growth factor-BB (1 ng/mL; 0.04 nmol/L) and in cells in which tyrosine kinase was inhibited by specific inhibitors (1 mumol/L tyrphostin A-23 and genistein). Ang II elicited a rapid and transient [Ca2+]i response (from 94 +/- 8 to 239 +/- 5.8 nmol/L). Activation of the receptor tyrosine kinase by insulin, platelet-derived growth factor, and insulin-like growth factor-I significantly reduced (P < .01) Ang II-induced [Ca2+]i to 161 +/- 7, 189 +/- 3.7, and 183 +/- 5 nmol/L, respectively. In the presence of tyrphostin A-23 and genistein, Ang II-stimulated [Ca2+]i remained persistently elevated and failed to return to basal levels. Tyrphostin A-1, the inactive tyrphostin analogue, had not significant effect on Ang II-induced [Ca2+]i. This study demonstrates that activation of tyrosine kinase pathways reduces Ang II-elicited [Ca2+]i responses, whereas tyrosine kinase inhibition prevents [Ca2+]i recovery after agonist stimulation. Interaction between tyrosine kinase- and phospholipase C-dependent signaling pathways modulates vascular smooth muscle cell [Ca2+]i responses to Ang II.

Effect of platelet-derived growth factor on voltage-operated calcium channels in rabbit isolated ear artery cells

1. Platelet derived growth factor (PDGF), AB and BB isoforms (100 pM) increased calcium channel currents measured by whole cell voltage clamp technique in single vascular smooth muscle cells isolated from rabbit ear arteries. 2. Tyrphostin-23 (100 microM) a selective inhibitor of protein tyrosine kinases, reduced calcium channel currents. Pre-incubation with tyrphostin-23 prevented PDGF-AB induced increase in calcium channel currents. However, in these same cells 10 nM (+)-202791, a dihydropyridine calcium channel agonist, did increase calcium channel currents. 3. Bistyrphostin (10 microM), a selective inhibitor of epidermal growth factor (EGF)-kinase also reduced calcium channel currents and inhibited PDGF-AB-induced increases in calcium channel currents. 4. Genistein (100 microM) a selective inhibitor of tyrosine kinases, structurally unrelated to the tryphostins, also inhibited calcium channel currents and pre-incubation with genistein prevented the PDGF-AB-induced rise in calcium channel currents. 5. These results indicate that PDGF increases calcium channel currents in vascular smooth muscle. This action of PDGF probably involves a tyrosine kinase.