Na(+)-H+ exchange inhibitors decrease neointimal formation after rat carotid injury. Effects on smooth muscle cell migration and proliferation

Rho kinase and Na+ /H+ exchanger mediate endothelin-1-induced pulmonary arterial smooth muscle cell proliferation and migration

Excessive production of endothelin‐1 (ET‐1) has been observed in almost all forms of pulmonary hypertension. ET‐1, a highly potent vasoconstrictor, can also potentiate pulmonary arterial smooth muscle cell (PASMC) growth and migration, both of which contribute to the vascular remodeling that occurs during the development of pulmonary hypertension. Increasing evidence indicates that alkalinization of intracellular pH (pH_i), typically due to activation of Na⁺/H⁺ exchange (NHE), is associated with enhanced PASMC proliferation and migration. We recently demonstrated that application of exogenous ET‐1 increased NHE activity in murine PASMCs via a mechanism requiring Rho kinase (ROCK). However, whether ROCK and/or increased NHE activity mediate ET‐1‐induced migration and proliferation in PASMCs remains unknown. In this study, we used fluorescent microscopy in transiently cultured PASMCs from distal pulmonary arteries of the rat and the pH‐sensitive dye, BCECF‐AM, to measure changes in resting pH_i and NHE activity induced by exposure to exogenous ET‐1 (10⁻⁸ mol/L) for 24 h. Cell migration and proliferation in response to ET‐1 were also measured using Transwell assays and BrdU incorporation, respectively. We found that application of exogenous ET‐1 had no effect on NHE1 expression, but increased pH_i, NHE activity, migration, and proliferation in rat PASMCs. Pharmacologic inhibition of NHE or ROCK prevented the ET‐1‐induced changes in cell function (proliferation and migration). Our results indicate that ET‐1 modulates PASMC migration and proliferation via changes in pH_i homeostasis through a pathway involving ROCK.

The Effect and Underlying Mechanism of Ethanol on Intracellular H(+) -Equivalent Membrane Transporters in Human Aorta Smooth Muscle Cells

BACKGROUND

The presence of intracellular pH (pHi ) regulators, including Na(+) -H(+) exchanger (NHE), Na(+) -HCO3- co-transporter (NBC), Cl(-) /OH(-) exchanger (CHE), and Cl(-) /HCO3- exchanger (AE), have been confirmed in many mammalian cells. Alcohol consumption is associated with increased risk of cardiovascular disorder. The aims of the study were to identify the possible transmembrane pHi regulators and to explore the effects of ethanol (EtOH) (10 to 300 mM) on the resting pHi and pHi regulators in human aorta smooth muscle cells (HASMCs).

METHODS

HASMCs were obtained from patients undergoing heart transplant. The pHi was measured by microspectrofluorimetry with the pH-sensitive dye, BCECF-AM.

RESULTS

The following results are obtained. (i) In cultured HASMCs, the resting pHi was 7.19 ± 0.04 and 7.13 ± 0.02 for HEPES- and CO2 /HCO3--buffered solution, respectively. (ii) Two different Na(+) -dependent acid-equivalent extruders, including NHE and Na(+) -coupled HCO3- transporter, functionally coexisted. (iii) Two different Cl(-) -dependent acid loaders (CHE and AE) were functionally identified. (iv) EtOH induced a biphasic, concentration-dependent change in resting pHi (+0.25 pH unit at 100 mM but only +0.05 pH unit at 300 mM) in bicarbonate-buffered solution, while caused a concentration-dependent decrease in resting pHi (-0.06 pH unit at 300 mM) in HEPES-buffered solution. (v) The effect of EtOH on NHE activity was also biphasic: increase of 40% at lower concentration of 10 mM, followed by decrease of 30% at higher concentration of 300 mM. (vi) The increase in Na(+) -coupled HCO3- transporter activity by EtOH was concentration dependent. (vii) The effect of EtOH on CHE and AE activities was both biphasic: increase of ~25% at 30 mM, followed by decrease of 10 to 25% at 100 mM, and finally increase of 15 to 20% at 300 mM.

CONCLUSIONS

This study demonstrated that 2 acid extruders and 2 acid loaders coexisted functionally in HASMCs and that EtOH induced a biphasic, concentration-dependent change in resting pHi by altering the activity of the 2 acid extruders, NHE and Na(+) -coupled HCO3- transporter, and the 2 acid loaders, CHE and AE.

High sodium augments angiotensin II-induced vascular smooth muscle cell proliferation through the ERK 1/2-dependent pathway

Angiotensin II (Ang II)-induced vascular injury is exacerbated by high-salt diets. This study examined the effects of high-sodium level on Ang II-induced cell proliferation in rat vascular smooth muscle cells (VSMCs). The cells were cultured in a standard medium containing 137.5 mmol l(-1) of sodium. The high-sodium medium (140 mmol l(-1)) contained additional sodium chloride. Extracellular signal-regulated kinase (ERK) 1/2 phosphorylation was determined by western blot analysis. Cell proliferation was evaluated by [(3)H]-thymidine incorporation. Ang II (100 nmol l(-1)) significantly increased ERK 1/2 phosphorylation and cell proliferation in the both medium containing standard sodium and high sodium. High-sodium level augmented Ang II-induced ERK 1/2 phosphorylation and cell proliferation compared with standard sodium. Pre-treatment with candesartan (1 μmol l(-1), Ang II type 1 receptor blocker) or PD98095 (10 μmol l(-1), ERK kinase iinhibitor) abolished the proliferative effect induced by high sodium/Ang II. Pre-treatment with 5-N,N-hexamethylene amiloride (30 μmol l(-1), Na(+)/H(+) exchanger type 1 (NHE-1) inhibitor), but not SN-6 (10 μmol l(-1), Na(+)/Ca(2+) exchanger inhibitor) or ouabain (1 mmol l(-1), Na(+)/K(+)-ATPase inhibitor) attenuated ERK 1/2 phosphorylation or cell proliferation. Osmotic pressure or chloride had no effect on Ang II-induced proliferative changes. High-sodium level did not affect Ang II receptor expression. Ang II increased intracellular pH via NHE-1 activation, and high-sodium level augmented the pH increase induced by Ang II. These data suggest that high-sodium level directly augments Ang II-induced VSMC proliferation through NHE-1- and ERK 1/2-dependent pathways and may offer new insights into the mechanisms of vascular remodeling by high-sodium/Ang II.

Endothelin-1 augments Na⁺/H⁺ exchange activity in murine pulmonary arterial smooth muscle cells via Rho kinase

Excessive production of endothelin-1 (ET-1), a potent vasoconstrictor, occurs with several forms of pulmonary hypertension. In addition to modulating vasomotor tone, ET-1 can potentiate pulmonary arterial smooth muscle cell (PASMC) growth and migration, both of which contribute to the vascular remodeling that occurs during the development of pulmonary hypertension. It is well established that changes in cell proliferation and migration in PASMCs are associated with alkalinization of intracellular pH (pH_i), typically due to activation of Na⁺/H⁺ exchange (NHE). In the systemic vasculature, ET-1 increases pH_i, Na⁺/H⁺ exchange activity and stimulates cell growth via a mechanism dependent on protein kinase C (PKC). These results, coupled with data describing elevated levels of ET-1 in hypertensive animals/humans, suggest that ET-1 may play an important role in modulating pH_i and smooth muscle growth in the lung; however, the effect of ET-1 on basal pH_i and NHE activity has yet to be examined in PASMCs. Thus, we used fluorescent microscopy in transiently (3–5 days) cultured rat PASMCs and the pH-sensitive dye, BCECF-AM, to measure changes in basal pH_i and NHE activity induced by increasing concentrations of ET-1 (10⁻¹⁰ to 10⁻⁸ M). We found that application of exogenous ET-1 increased pH_i and NHE activity in PASMCs and that the ET-1-induced augmentation of NHE was prevented in PASMCs pretreated with an inhibitor of Rho kinase, but not inhibitors of PKC. Moreover, direct activation of PKC had no effect on pH_i or NHE activity in PASMCs. Our results indicate that ET-1 can modulate pH homeostasis in PASMCs via a signaling pathway that includes Rho kinase and that, in contrast to systemic vascular smooth muscle, activation of PKC does not appear to be an important regulator of PASMC pH_i.

The amiloride derivative phenamil attenuates pulmonary vascular remodeling by activating NFAT and the bone morphogenetic protein signaling pathway

Pulmonary artery hypertension (PAH) is characterized by elevated pulmonary artery resistance and increased medial thickness due to deregulation of vascular remodeling. Inactivating mutations of the BMPRII gene, which encodes a receptor for bone morphogenetic proteins (BMPs), are identified in ∼60% of familial PAH (FPAH) and ∼30% of idiopathic PAH (IPAH) patients. It has been hypothesized that constitutive reduction in BMP signal by BMPRII mutations may cause abnormal vascular remodeling by promoting dedifferentiation of vascular smooth muscle cells (vSMCs). Here, we demonstrate that infusion of the amiloride analog phenamil during chronic-hypoxia treatment in rat attenuates development of PAH and vascular remodeling. Phenamil induces Tribbles homolog 3 (Trb3), a positive modulator of the BMP pathway that acts by stabilizing the Smad family signal transducers. Through induction of Trb3, phenamil promotes the differentiated, contractile vSMC phenotype characterized by elevated expression of contractile genes and reduced cell growth and migration. Phenamil activates the Trb3 gene transcription via activation of the calcium-calcineurin-nuclear factor of activated T cell (NFAT) pathway. These results indicate that constitutive elevation of Trb3 by phenamil is a potential therapy for IPAH and FPAH.

The effects of amiloride, a Na+-H+ exchange inhibitor, on iliac artery stenosis after balloon injury in rabbits

This study was designed to explore the effects of amiloride, a Na+-H+ exchange (NHE) inhibitor, on vessel stenosis by observing the expression of NHE-1 protein in vascular smooth muscle (VSM) after balloon injury and the effects of amiloride on VSM cell proliferation, migration, and excretion of extracellular matrices (ECMs). A total of 32 adult male New Zealand white rabbits were randomly divided into a balloon injury group (BG), an amiloride-treated group (AG), and a sham-operated group (SG). The left iliac artery was injured by inflating a 2.5 mm x 20 mm Foley catheter in BG and AG rabbits; in SG rabbits, the Foley catheter was inserted but not inflated. Amiloride (5 mg x kg(-1) x d(-1)) was injected intraperitoneally in AG and the same volume of distilled water was used in BG 3 days before balloon injury and for 28 days after the injury. The left iliac artery was stained by hematoxylin-eosin, alpha-actin, and Masson's trichrome to observe the vessel cava, neointima, media layer, and ECMs. NHE-1 proteins of the VSM were detected by Western blotting. A narrowing of the arterial cava, neointima formation, and thickened VSM layer were observed 28 days after balloon injury in BG and AG. However, in AG, the vessel cava was not as narrowed as that of BG and the intimal areas were to a lesser extent than in BG. In AG, the alpha-actin-positive areas and the ECM areas in the neointima were increased compared with SG, but to a lesser extent than in BG. The expression of NHE-1 protein in VSM was increased in BG and AG after balloon injury; however, the levels in AG were significantly less than in BG. In conclusion, VSM cell proliferation, migration, and excretion of ECMs contributed to vessel stenosis in the BG and AG rabbits. The expression of NHE-1 protein in VSM increased after balloon injury. Amiloride, an inhibitor of NHE-1, can limit the development of vessel stenosis through inhibition of VSM cell proliferation, migration, and excretion of ECMs.

Novel roles of intracrine angiotensin II and signalling mechanisms in kidney cells

Angiotensin II (Ang II) has powerful sodium-retaining, growth-promoting and pro- inflammatory properties in addition to its physiological role in maintaining body salt and fluid balance and blood pressure homeostasis. Increased circulating and local tissue Ang II is one of the most important factors contributing to the development of sodium and fluid retention, hypertension and target organ damage. The importance of Ang II in the pathogenesis of hypertension and target organ injury is best demonstrated by the effectiveness of angiotensin- converting enzyme (ACE) inhibitors and AT1-receptor antagonists in treating hypertension and progressive renal disease including diabetic nephropathy. The detrimental effects of Ang II are mediated primarily by the AT1-receptor, while the AT2-receptor may oppose the AT1-receptor. The classical view of the AT1-receptor-mediated effects of Ang II is that the agonist binds its receptors at the cell surface, and following receptor phosphorylation, activates downstream signal transduction pathways and intracellular responses. However, evidence is emerging that binding of Ang II to its cell surface AT1-receptors also activates endocytotic (or internalisation) processes that promote trafficking of both the effector and the receptor into intracellular compartments. Whether internalised Ang II has important intracrine and signalling actions is not well understood. The purpose of this article is to review recent advances in Ang II research with focus on the mechanisms underlying high levels of intracellular Ang II in proximal tubule cells and the contribution of receptor-mediated endocytosis of extracellular Ang II. Further attention is devoted to the question whether intracellular and/or internalised Ang II plays a physiological role by activating cytoplasmic or nuclear receptors in proximal tubule cells. This information may aid future development of drugs to prevent and treat Ang II-induced target organ injury in cardiovascular and renal diseases by blocking intracellular and/or nuclear actions of Ang II.

Inhibition of Human Pulmonary Artery Smooth Muscle Cell Proliferation and Migration by Sabiporide, a New Specific NHE-1 Inhibitor

Abnormal growth of vascular smooth muscle cells is seen in various pathological conditions such as hypertension, atherosclerosis, and restenosis. Na/H exchanger (NHE) activation appears to play a permissive role in vascular smooth muscle cell proliferation and vascular remodeling. The present study investigated the effect of a new specific NHE-1 inhibitor, sabiporide, on human pulmonary artery smooth muscle cell proliferation and migration. Concentrations of sabiporide as low as 20 micromol/L in the culture medium containing growth factors inhibited cell proliferation, as measured by cell counting, and also inhibited the rate of DNA synthesis, as examined by measuring BrdU incorporation into DNA. Cell growth inhibition was not caused by cell death, as demonstrated by the measurement of intracellular lactate dehydrogenase release and by the reversibility of inhibition upon washing. By fluorescent-activated cell sorting analysis, we are the first to demonstrate that NHE-1 inhibition arrests the cell cycle progression at G0/G1 phase, suggesting that NHE activation plays a permissive role in entrance of cells into the cell cycle. Sabiporide also concentration-dependently inhibited human pulmonary artery smooth muscle cell migration. The present study showed that sabiporide inhibits vascular smooth muscle cell proliferation and migration by blocking the cell cycle progression at G0/G1 phase.

Functional role of Na+-HCO3- cotransport in migration of transformed renal epithelial cells

Cell migration is crucial for immune defence, wound healing or formation of tumour metastases. It has been shown that the activity of the Na(+)-H(+) exchanger (NHE1) plays an important role in cell migration. However, so far it is unknown whether Na(+)- HCO(3)(-) cotransport (NBC), which has similar functions in the regulation of intracellular pH (pH(i)) as NHE1, is also involved in cell migration. We therefore isolated NHE-deficient Madin-Darby canine kidney (MDCK-F) cells and tested whether NBC compensates for NHE in pH(i) and cell volume regulation as well as in migration. Intracellular pH was measured with the fluorescent pH indicator 2'7'-bis(carboxyethyl)-5-carboxyfluorescein (BCECF). The expression of NBC isoforms was determined with semiquantitative PCR. Migration was monitored with time-lapse video microscopy and quantified as the displacement of the cell centre. We found that MDCK-F cells express the isoform NBC1 (SLCA4A gene product) at a much higher level than the isoform kNBC3 (SLCA4A8 gene product). This difference is even more pronounced in NHE-deficient cells so that NBC1 is likely to be the major acid extruder in these cells and the major mediator of propionate-induced cell volume increase. NHE-deficient MDCK-F cells migrate more slowly than normal MDCK-F cells. NBC activity promotes migration during an acute intracellular acid load and increases migratory speed and displacement on a short timescale (< 30 min) whereas it has no effect on the long-term behaviour of migrating MDCK-F cells. Taken together, our results show that NBC actvity, despite many functional similarities, does not have the same importance for cell migration as NHE1 activity.

Chronic hypoxia elevates intracellular pH and activates Na+/H+ exchange in pulmonary arterial smooth muscle cells

Chronic hypoxia (CH), caused by many lung diseases, results in pulmonary hypertension due, in part, to increased muscularity of small pulmonary vessels. Pulmonary arterial smooth muscle cell (PASMC) proliferation in response to growth factors requires increased intracellular pH (pHi) mediated by activation of Na+/H+ exchange (NHE); however, the effect of CH on PASMC pHi homeostasis is unknown. Thus we measured basal pHi and NHE activity and expression in PASMCs isolated from mice exposed to normoxia or CH (3 wk/10% O2). pHi was measured using the pH-sensitive fluorescent dye BCECF-AM. NHE activity was determined from Na+-dependent recovery from NH4-induced acidosis, and NHE expression was determined by RT-PCR and immunoblot. PASMCs from chronically hypoxic mice exhibited elevated basal pHi and increased NHE activity. NHE1 was the predominate isoform present in mouse PASMCs, and both gene and protein expression of NHE1 was increased following exposure to CH. Our findings indicate that exposure to CH caused increased pHi, NHE activity, and NHE1 expression, changes that may contribute to the development of pulmonary hypertension, in part, via pH-dependent induction of PASMC proliferation.

ERK Is Regulated by Sodium-Proton Exchanger in Rat Aortic Vascular Smooth Muscle Cells

The purposes of this study were to test 1) the relationship between two widely studied mitogenic effector pathways, and 2) the hypothesis that sodium-proton exchanger type 1 (NHE-1) is a regulator of extracellular signal-regulated protein kinase (ERK) activation in rat aortic smooth muscle (RASM) cells. Angiotensin II (Ang II) and 5-hydroxytryptamine (5-HT) stimulated both ERK and NHE-1 activities, with activation of NHE-1 preceding that of ERK. The concentration-response curves for 5-HT and Ang II were superimposable for both processes. Inhibition of NHE-1 with pharmacological agents or by isotonic replacement of sodium in the perfusate with choline or tetramethylammonium greatly attenuated ERK activation by 5-HT or Ang II. Similar maneuvers significantly attenuated 5-HT- or Ang II-mediated activation of MEK and Ras but not transphosphorylation of the epidermal growth factor (EGF) receptor. EGF receptor blockade attenuated ERK activation, but not NHE-1 activation by 5-HT and Ang II, suggesting that the EGF receptor and NHE-1 work in parallel to stimulate ERK activity in RASM cells, converging distal to the EGF receptor but at or above the level of Ras in the Ras-MEK-ERK pathway. Receptor-independent activation of NHE-1 by acute acid loading of RASM cells resulted in the rapid phosphorylation of ERK, which could be blocked by pharmacological inhibitors of NHE-1 or by isotonic replacement of sodium, closely linking the proton transport function of NHE-1 to ERK activation. These studies identify NHE as a new regulator of ERK activity in RASM cells.

Ethyl isopropyl amiloride inhibits smooth muscle cell proliferation and migration by inducing apoptosis and antagonizing urokinase plasminogen activator activity

Amiloride inhibits activation of the Na(+)-H+ exchanger (NHE), a critical step in smooth muscle cell (SMC) growth. While amiloride treatment reduces SMC proliferation and migration, as well as experimental lesion formation, these effects are not exclusively due to NHE inhibition and remain incompletely understood. The purpose of this study was to examine the mechanisms involved in amiloride-induced attenuation of SMC proliferation and migration, looking specifically at the potential role of apoptosis and urokinase plasminogen activator (uPA) activity in these processes. Rabbit SMCs in tissue culture were exposed to 10-80 microM of the amiloride analogue ethyl isopropyl amiloride (EIPA). Compared with controls, EIPA reduced DNA synthesis, cell number, and mitochondrial respiration, but without toxic effects on quiescent or proliferating cells. In a Boyden chamber assay, EIPA reduced uPA-induced SMC migration. Moreover, in a SMC scratch assay EIPA treatment resulted in a 66% reduction in the number of repopulating cells, a 92% decrease in the number of proliferating cells, and a 37-fold increase in the number of apoptotic cells. SMC apoptosis was frequently localized to the scratch edges, where cell proliferation and bcl-2 expression were absent. Finally, uPA enzymatic activity in the cell culture media was lower for EIPA-treated versus control SMCs. Therefore, EIPA inhibits both SMC proliferation and migration by inducing apoptosis and antagonizing uPA activity, respectively, and requires further study as an agent for reducing vascular lesion formation.

Rho-Rho kinase is involved in smooth muscle cell migration through myosin light chain phosphorylation-dependent and independent pathways

Although Rho, a small GTPase, has been demonstrated to play an important role in the smooth muscle contraction and relaxation, little is known about the involvement of Rho protein in smooth muscle cell (SMC) migration. In this study the role of Rho-Rho kinase pathway was examined in SMC migration induced by platelet-derived growth factor (PDGF) and lysophosphatidic acid (LPA). C3 transferase, a specific inhibitor of Rho, blocked SMC migration induced by PDGF and LPA. Y-27632, a specific inhibitor of Rho kinase, a direct target molecule of Rho, inhibited PDGF and LPA-induced SMC migration in a concentration dependent manner. Although rapid increase in myosin light chain (MLC) phosphorylation in SMC treated with LPA was observed, no enhanced MLC phosphorylation was detected in response to PDGF. Y-27632 suppressed LPA-induced as well as basal level of MLC phosphorylation. ML-9, a specific inhibitor of myosin light chain kinase (MLCK), inhibited PDGF and LPA-induced SMC migration without the suppression of MLC phosphorylation at 5 min incubation, suggesting that MLCK may contribute to SMC migration via mechanism other than MLC phosphorylation. These results suggest that Rho-Rho kinase pathway is implicated in SMC migration and that different signaling pathways downstream of Rho-Rho kinase may be involved in LPA and PDGF-induced SMC migration. MLC phosphorylation via Rho-Rho kinase pathway appears to be implicated in LPA-dependent SMC migration. Whereas PDGF-mediated SMC migration is independent of increased MLC phosphorylation and other target molecules downstream of Rho-Rho kinase seem to be involved.

Heme oxygenase-1 attenuates vascular remodeling following balloon injury in rat carotid arteries

The heme oxygenase-1 (HO-1) system of heme catabolism has been proposed to exert protective actions upon the cardiovascular system. This investigation examined the influence of HO-1 induction on vascular remodeling following arterial injury. Rats were subjected to left carotid artery (LCA) balloon injury following pre-treatment with either vehicle, the HO-1 inducer hemin (50 mg/kg, SC), or concomitant treatment with hemin and the HO-1 inhibitor tin-protoporphyrin IX (SnPP-IX; 50 micromol/kg, IP). Animals were injected daily for 14 days post-injury, after which animals were sacrificed and tissues obtained. Western blot analyses revealed vascular HO-1 induction after 2 and 16 days of hemin treatment. Positive immunostaining for HO-1 was detected in the endothelial and adventitial layers following 48 h of hemin treatment and positive medial staining for HO-1 after 16 days of hemin treatment. The injured LCA of hemin-treated animals demonstrated significantly attenuated neointimal (NI) area (-57%), NI thickness (-58%), and NI area/medial wall area ratio (-40%) compared to the injured LCA of vehicle controls. The cross-sectional medial wall areas of both LCA and uninjured RCA were also significantly reduced in the hemin-treated animals. SnPP-IX treatment, however, completely restored the NI area, NI thickness, NI area/medial wall area ratio, and partially restored the medial wall area towards control levels. These results directly implicate HO-1 and the products of heme catabolism in attenuating the arterial response to injury and ensuing vascular wall remodeling.

Abnormal proliferative response of the carotid artery of spontaneously hypertensive rats after angioplasty may be related to the depolarized state of its smooth muscle cells

Hypertension is one of the major precursors of atherosclerotic vascular disease, and vascular smooth muscle abnormal cell replication is a key feature of plaque formation. The present study was conducted to examine the relationship between hypertension and smooth muscle cell proliferation after balloon injury and to correlate neointima formation with resting membrane potential of uninjured smooth muscle cells, since it has been suggested that altered vascular function in hypertension may be related to the resetting of the resting membrane potential in spontaneously hypertensive rats (SHR). Neointima formation was induced by balloon injury to the carotid arteries of SHR and renovascular hypertensive rats (1K-1C), as well as in their normotensive controls, i.e., Wistar Kyoto (WKY) and normal Wistar (NWR) rats. After 14 days the animals were killed and the carotid arteries were submitted to histomorphometric and immunohistochemical analyses. Resting membrane potential measurements showed that uninjured carotid arteries from SHR smooth muscle cells were significantly depolarized (-46.5 +/- 1.9 mV) compared to NWR (-69 +/- 1.4 mV), NWR 1K-1C (-60.8 +/- 1.6 mV), WKY (-67.1 +/- 3.2 mV) and WKY 1K-1C (-56.9 +/- 1.2 mV). The SHR arteries responded to balloon injury with an enhanced neointima formation (neo/media = 3.97 +/- 0.86) when compared to arteries of all the other groups (NWR 0.93 +/- 0.65, NWR 1K-1C 1.24 +/- 0.45, WKY 1.22 +/- 0.32, WKY 1K-1C 1.15 +/- 0.74). Our results indicate that the increased fibroproliferative response observed in SHR is not related to the hypertensive state but could be associated with the resetting of the carotid smooth muscle cell resting membrane potential to a more depolarized state.

MAP kinases and vascular smooth muscle function

The mitogen-activated protein (MAP) kinase family members are ubiquitously expressed protein kinases activated in response to a variety of extracellular stimuli and shown to be involved in cell growth, transformation, differentiation and apoptosis. MAP kinases have been implicated in both growth and apoptosis of vascular smooth muscle cells (VSMC) which suggests that they play important roles in cardiovascular diseases such as essential hypertension, atherosclerosis, and restenosis followed angioplasty. The MAP kinases are themselves components of specific kinase cascades characterized by activation by specific stimuli, families of related serine and threonine kinases and downstream substrates that include other kinases, transcription factors, membrane receptors and other cell mediators. Cross-talk among the different MAP kinases results in direct modulation of signal transduction. In addition, increased expression and activation of MAP kinase phosphatases plays an important role in MAP kinase inactivation. Our laboratory has used angiotensin II (AngII), a potent activator of all MAP kinases in VSMC, to study mechanisms by which MAP kinases are regulated by vasoactive peptides. In this review, we describe the mechanisms by which AngII activates MAP kinases, and potential roles for MAP kinases in AngII-dependent effects on VSMC function.

Amiloride analogs inhibit chronic hypoxic pulmonary hypertension

Na+/H+ exchange regulation of intracellular pH may play a permissive role in pulmonary artery smooth muscle cell (PASM) proliferation. Our laboratory has demonstrated that dimethyl amiloride (DMA), an amiloride derivative with enhanced selectivity as an inhibitor of the Na+/H+ antiporter, can inhibit bovine PASM proliferation in vitro. We hypothesized that DMA would inhibit development of hypoxic pulmonary hypertension by interfering with PASM growth in vivo. Sprague-Dawley rats were exposed to 10% O2 for 14 d without (n 9) or with (n = 7) DMA continuous infusion 3 mg/ kg/d. The animals treated with DMA had significant reductions in pulmonary artery pressure and total pulmonary vascular resistance index (TPVRI) when compared with hypoxic control rats (p < 0.05). Pulmonary vascular remodeling was significantly reduced in animals treated with DMA as measured by percent wall thickness and percentage of thick-walled intra-acinous vessels (p < 0.05). We used a second Na+/H+ exchange inhibitor, ethylisopropyl amiloride (EIPA, 3 mg/kg/d, n = 9), and found similar reductions in pulmonary artery pressure, TPVRI, and pulmonary vascular remodeling. Polycythemia during hypoxia was unchanged by treatment with DMA or EIPA. In conclusion, despite the hypertensive effects of polycythemia, DMA and EIPA can significantly reduce pulmonary vascular remodeling induced by chronic hypoxia.

Effect of the Na+/H+ antiport inhibitor Hoe 694 on the angiotensin II-induced vascular smooth muscle cell growth

1. Hoe 694 (3-methylsulphonyl-4-piperidinobenzoyl)guanidine methanesulphonate) was characterized as a new, potent, non-amiloride inhibitor of the Na+/H+ exchanger. In order to elucidate the role of the Na+/H+ exchanger isoform 1 (NHE-1) in the regulation of vascular smooth muscle cell growth, we investigated the effects of different amiloride analogues and of Hoe 694 on angiotensin II-induced cell growth. Since intracellular pH, the intracellular free Ca2+ concentration and the expression of the transcription factor c-fos seem to be involved in the regulation of cell growth, the effects of the amiloride analogues and Hoe 694 on the angiotensin II-induced changes in these three parameters were examined. 2. Measurement of cytosolic Ca2+ and pH in cell monolayers was performed using fura-2/AM and BCECF/AM, respectively. The effect of angiotensin II on cell growth was examined using (1) [3H]-thymidine incorporation, (2) the bromo-2-deoxyuridine (BrdU) immunfluorescence assay, (3) the colorimetric determination of cell mitochondrial dehydrogenase activity and (4) determination of cell number. Total RNA was extracted from cells by the guanidinium isothiocyanate/CsCl procedure. The expression of c-fos was quantitated by Northern blotting. 3. Various amiloride analogues inhibited the angiotensin II-induced stimulation of the Na+/H+ exchanger, the increase in cytosolic Ca2+ and cell growth but not the induction of c-fos mRNA. Hoe 694 (1-25 microM) dose-dependently inhibited the angiotensin II-induced stimulation of the Na+/H+ exchanger but had no significant effects on cytosolic Ca2+, c-fos mRNA levels or cell growth. 4. Our findings support the concept that activation of the Na+/H+ exchanger is not essential for angiotensin II-induced vascular smooth muscle cell growth.

Growth phenotype of cultured skin fibroblasts from IDDM patients with and without nephropathy and overactivity of the Na+/H+ antiporter

An increased activity of the Na+/H+ antiporter in cells from patients with insulin-dependent diabetes mellitus (IDDM) has been proposed as a potential marker of nephropathy. We evaluated Na+/H+ antiporter activity and its relationship to DNA and protein synthesis in cultured skin fibroblasts from patients with IDDM classified as having either overt nephropathy or absence of nephropathy on the basis of urinary albumin excretion and kidney biopsy findings. In IDDM patients with overt nephropathy, Na+/H+ antiporter activity in serum stimulated cells was increased as compared to cells from control subjects (9.62 +/- 0.89 vs. 5.67 +/- 0.97 mmol H+/min, P < 0.005, respectively) and cells from IDDM patients without nephropathy (7.22 +/- 0.67 mmol H+/min, P < 0.025). By contrast, in cells made quiescent by serum deprivation Na+/H+ antiporter activity was lower than in serum-stimulated cells and there were no significant differences between the three groups. DNA synthesis assessed by [3H] thymidine incorporation was increased in the IDDM group with nephropathy as compared to the group without nephropathy (138 +/- 14 vs. 105 +/- 13 cpm/1000 cells, respectively, P < 0.05) and as compared to control subjects (65 +/- 11 cpm/1000 cells, P < 0.001). By contrast, protein synthesis assessed by [14C] L-leucine incorporation was not increased in fibroblasts from IDDM patients with nephropathy, suggesting that cellular hypertrophy is not a feature of their altered growth phenotype. After chronic inhibition of the Na+/H+ antiporter using EIPA (25 microM), [3H] thymidine incorporation was reduced by about 20% both in cells from IDDM patients and controls. This parameter therefore remained higher in cells from IDDM patients with nephropathy than in those from controls (81 +/- 16 vs. 40 +/- 6 cpm/1000 cells, P < 0.05), while in cells from IDDM patients without nephropathy [3H] thymidine incorporation after EIPA (56 +/- 7.0 cpm/1000 cells) was intermediate between cells from controls and IDDM patients with nephropathy. We argue that cultured skin fibroblasts from IDDM patients, with nephropathy display an abnormal growth phenotype characterized by cell hyperplasia. This growth phenotype is associated with overactivity of the Na+/H+ antiporter during serum stimulation but not when cells are made quiescent and persists after inhibition of the Na+/H+ antiporter. Our data, therefore, further shows that overactivity of the Na+/H+ antiporter is not required for the expression of the altered growth phenotype of cultured skin fibroblasts from IDDM patients with nephropathy.

Tranilast suppresses intimal hyperplasia in the balloon injury model and cuff treatment model in rabbits

Intimal hyperplasia is a serious problem after percutaneous transluminal coronary angioplasty (PTCA). In this study, we investigated the effects of tranilast on intimal hyperplasia in both in vivo and in vitro experiments. For the in vivo experiments, we used the balloon injury model and the cuff treatment model of rabbits fed regular chow. In the balloon injury model, tranilast decreased intimal area, intima/media ratio, stenosis ratio and vascular DNA content after endothelial injury. Also in the cuff treatment model, tranilast suppressed the intimal hyperplasia. In the in vitro experiments, we assessed the effects of tranilast on platelet-derived growth factor-induced rabbit vascular smooth muscle cell (VSMC) migration and proliferation and on collagen synthesis by VSMCs. Tranilast inhibited VSMC migration, proliferation and collagen synthesis. These results suggest that tranilast has a suppressive effect on intimal hyperplasia after a vascular injury such as PTCA.