Analysis of angiotensin-stimulated sodium transport in cultured smooth muscle cells from rat aorta

Sodium-activated potassium channels moderate excitability in vascular smooth muscle

KEY POINTS

We report that a sodium-activated potassium current, IKNa , has been inadvertently overlooked in both conduit and resistance arterial smooth muscle cells. IKNa is a major K+ resting conductance and is absent in cells of IKNa knockout (KO) mice. The phenotype of the IKNa KO is mild hypertension, although KO mice react more strongly than wild-type with raised blood pressure when challenged with vasoconstrictive agents. IKNa is negatively regulated by angiotensin II acting through Gαq protein-coupled receptors. In current clamp, KO arterial smooth muscle cells have easily evoked Ca2+ -dependent action potentials.

ABSTRACT

Although several potassium currents have been reported to play a role in arterial smooth muscle (ASM), we find that one of the largest contributors to membrane conductance in both conduit and resistance ASMs has been inadvertently overlooked. In the present study, we show that IKNa , a sodium-activated potassium current, contributes a major portion of macroscopic outward current in a critical physiological voltage range that determines intrinsic cell excitability; IKNa is the largest contributor to ASM cell resting conductance. A genetic knockout (KO) mouse strain lacking KNa channels (KCNT1 and KCNT2) shows only a modest hypertensive phenotype. However, acute administration of vasoconstrictive agents such as angiotensin II (Ang II) and phenylephrine results in an abnormally large increase in blood pressure in the KO animals. In wild-type animals Ang II acting through Gαq protein-coupled receptors down-regulates IKNa , which increases the excitability of the ASMs. The complete genetic removal of IKNa in KO mice makes the mutant animal more vulnerable to vasoconstrictive agents, thus producing a paroxysmal-hypertensive phenotype. This may result from the lowering of cell resting K+ conductance allowing the cells to depolarize more readily to a variety of excitable stimuli. Thus, the sodium-activated potassium current may serve to moderate blood pressure in instances of heightened stress. IKNa may represent a new therapeutic target for hypertension and stroke.

Role of miR-145 in cardiac myofibroblast differentiation

Following a myocardial infarction (MI), fibroblasts differentiate to myofibroblasts, which possess some of the characteristics of smooth muscle cells (SMCs) and contribute to wound healing. Previous studies suggested that the miR-143/-145 cluster plays a critical role in SMC differentiation. Therefore, we determined whether miR-145 promoted differentiation of cardiac fibroblasts to myofibroblasts. Following coronary occlusion in mice, myocardial miR-145 expression was downregulated at 3 days but was restored at 7 days. In vitro studies showed that hypoxia also downregulated miR-145 in cardiac fibroblasts. The number of α-smooth muscle actin (α-SMA) positive cells in fibroblast cultures was employed to determine their transdifferentiation to cardiac myofibroblasts and was increased by 73.5% after transient transfection with miR-145. Ultrastructural analysis of α-SMA stress fibers revealed that ~95% of the α-SMA(+) cells treated with miR-145 organized their actin-filament bundles with a specific orientation compared to only 15% in the scrambled control group. This orientation of the SMA bundles and their integration with the filamentous actin fibers of the cytoskeleton permit infarct wound contraction. Structural and functional studies showed that miR-145 induced a myofibroblast phenotype, and miR-145 also potentiated the production of mature collagen by myofibroblasts. Repression of KLF5, a target of miR-145, was validated by a chimeric luciferase construct tagged with the full-length 3'-UTR of KLF5. A dramatic decrease in KLF5 and a corresponding increase in myocardin expression were observed after transfecting cultured fibroblasts with miR-145. Similar results were found in vivo: the transient decrease in miR-145 expression 3 days post-MI was associated with an increase in KLF5 and a decrease in myocardin. In addition, in vivo delivery of a miR-145 antagomir 1 day prior to and 2 and 6 days after MI decreased myofibroblast formation and increased scar size. The antagomir also reversed the suppressed expression of KLF5 protein in the scar region at day 7 after MI. In summary, we describe a novel association between miR-145 and fibroblast differentiation toward myofibroblasts. These observations provide a new approach to promote endogenous scar healing and contracture by stimulating the transdifferentiation of cardiac fibroblasts to myofibroblasts.

Selenium suppressed hydrogen peroxide-induced vascular smooth muscle cells calcification through inhibiting oxidative stress and ERK activation

Atherosclerosis is frequently associated with vascular calcification. Increasing evidences underline that the essential micronutrient selenium may prevent atherosclerosis, but the role of selenium in vascular calcification remains unknown. In this study, we assessed the effect of sodium selenite (Na(2)SeO(3)) on H(2)O(2)-enhanced vascular smooth muscle cells (VSMCs) calcification and examined the involvement of extracellular signal-regulated kinase (ERK) signaling pathway. Hydrogen peroxide enhanced vascular calcification by inducing osteoblastic differentiation of VSMCs, as showed by up-regulating the mRNA expression of type I collagen, osteocalcin, and Runx2, a key transcription factor for osteoblastic differentiation, increasing alkaline phosphatase activity, and calcium deposition. These effects of H(2)O(2) were suppressed by pretreatment of the cells with selenite (0.1-1 µM) for 24 h. In addition, H(2)O(2) activated the phosphorylation of ERK1/2 and inhibition of H(2)O(2)-activated ERK signaling by MEK inhibitor PD98059 blocked the effect of H(2)O(2) on osteoblastic differentiation of VSMCs. Furthermore, H(2)O(2) induced oxidative stress in calcifying VSMCs, as evidenced by the increase of intracellular reactive oxygen species production and malondialdehyde level, and the decrease of total protein thiols content and the activity of antioxidant selenoenzyme glutathione peroxidases. Selenite pretreatment also attenuated H(2)O(2)-induced oxidative stress and ERK activation. These results suggested that selenite suppressed H(2)O(2)-enhanced osteoblastic differentiation and calcification of VSMCs through inhibiting oxidative stress and ERK activation, indicating a potential preventive role for selenium in vascular calcification.

Increased static pressure promotes migration of vascular smooth muscle cells: involvement of the Rho-kinase pathway

Vascular smooth muscle cell (VSMC) migration plays a pivotal role in the pathogenesis of arteriosclerosis, under influences of various mechanical factors. Thus, we examined whether static pressure promotes VSMC migration and if so, whether Rho-kinase is involved. Rat VSMCs were cultured on chambers coated on fibronectin, vitronectin, laminin, or type IV collagen, under pressure-free conditions and at 90 and 180 mm Hg. In monolayer-wounding assay, VSMC migration was significantly increased after 72 hours at 180 mm Hg on both fibronectin (11.3 +/- 3.4-fold vs. pressure-free conditions) and vitronectin (10.6 +/- 0.7-fold; both P < 0.05). In Boyden chamber assay, the VSMC migration was again significantly increased at 180 mm Hg on both fibronectin (4.0 +/- 0.5-fold) and vitronectin (5.0 +/- 0.8-fold; both P < 0.05). Neutralizing antibodies against beta1-, beta3- and beta5-integrins, all of which play an important role in cell migration, significantly inhibited the pressure-promoted VSMC migration. Static pressure also significantly increased Rho-kinase activity in VSMC, as evaluated by the extent of phosphorylation of its downstream substrate, ezrin-radixin-moesin. Fasudil, a selective Rho-kinase inhibitor, significantly suppressed the pressure-promoted VSMC migration with reduced Rho-kinase activity. These results indicate that increased static pressure promotes VSMC migration through the integrin/Rho-kinase signaling, suggesting the therapeutic importance of this mechanism for the treatment of hypertensive vascular diseases.

Movement of acid equivalents across the mammalian smooth muscle cell membrane

Factors affecting intracellular pH (pHi) in the smooth muscle of guinea pig ureter have been investigated using pH-sensitive microelectrodes. Associated acids and bases appear to have free passage across the cell membrane but results suggest very low permeability to charged acid equivalents, thus implicating carrier-mediated movements in many of the observed pHi transients. Recovery from acidosis in the nominal absence of CO2 was inhibited by removal of Na+ and by the presence of amiloride, indicating that Na+/H+ exchange was responsible. The presence of CO2 resulted in a faster recovery from acidosis but, since intracellular buffering power was not increased, not a substantially faster effective extrusion of protons. Surprisingly, amiloride no longer caused discernable inhibition. Recovery from moderate acidosis remained Na+ dependent but was not inhibited by DIDS or acetazolamide or by the absence of Cl-, suggesting a dominant Na+-, and HCO3(-)-dependent mechanism unlike any hitherto described. Recovery from alkalosis was inhibited by DIDS and Cl(-)-free conditions, indicating that Cl-/HCO3- exchange was involved. Results suggest reversal of this mechanism on extreme acidosis. Experiments in vascular smooth muscle with fluorescent indicators confirm the presence of Na+/H+ exchange but provide conflicting evidence about the presence and properties of the HCO3(-)-dependent mechanism.

Glucose down-regulation of cGMP-dependent protein kinase I expression in vascular smooth muscle cells involves NAD(P)H oxidase-derived reactive oxygen species

Reduced levels of cGMP-dependent protein kinase I (PKG-I) in vasculature have been shown to contribute to diabetic vascular dysfunctions. However, the underlying mechanisms remain unknown. In this report, using primary rat aortic smooth muscle cells (VSMC), we investigated the mechanisms of glucose-mediated regulation of PKG-I expression. Our data showed that high glucose (30 mM glucose) exposure significantly reduced PKG-I production (protein and mRNA levels) as well as PKG-I activity in cultured VSMC. Glucose-mediated decreases in PKG-I levels were inhibited by a superoxide scavenger (tempol) or NAD(P)H oxidase inhibitors (diphenylene iodonium or apocynin). High glucose exposure time-dependently increased superoxide production in VSMC, which was abolished by tempol or apocynin treatment, but not by other inhibitors of superoxide-producing enzymes (L-NAME, rotenone, or oxypurinol). Total protein levels and phosphorylated levels of p47phox (an NADPH oxidase subunit) were increased in VSMC after high glucose exposure. Transfection of cells with siRNA-p47phox abolished glucose-induced superoxide production and restored PKG-I protein levels in VSMC. Treatment of cells with PKC inhibitor prevented glucose-induced p47phox expression/phosphorylation and superoxide production and restored the PKG-I levels. Decreased PKG-I protein levels were also found in femoral arteries from diabetic mice, which were associated with the decreased DEA-NONOate-induced vasorelaxation. Taken together, the present results suggest that glucose-mediated down-regulation of PKG-I expression in VSMC occurs through PKC-dependent activation of NAD(P)H oxidase-derived superoxide production, contributing to diabetes-associated vessel dysfunctions.

Ral-GTPase interacts with the β1 subunit of Na+/K+-ATPase and is activated upon inhibition of the Na+/K+pumpThis paper is one of a selection of papers published in this Special Issue, entitled The Cellular and Molecular Basis of Cardiovascular Dysfunction, Dhalla 70th Birthday Tribute

Na+/K+-ATPase functions as both an ion pump and a signal transducer. Cardiac glycosides partially inhibit Na+/K+-ATPase, causing activation of multiple interrelated growth pathways via the Na+/K+-ATPase/c-Src/epidermal growth factor receptor complex. Such pathways include Ras/MEK/ERK and Ral/RalGDS cascades, which can lead to cardiac hypertrophy. In search of novel Ral-GTPase binding proteins, we used RalB as the bait to screen a human testes cDNA expression library using the yeast 2-hybrid system. The results demonstrated that 1 of the RalB interacting clones represented the C-terminal region of the β1 subunit of Na+/K+-ATPase. Further analysis using the yeast 2-hybrid system and full-length β1 subunit of Na+/K+-ATPase confirmed the interaction with RalA and RalB. In vitro binding and pull-down assays demonstrated that the β1 subunit of Na+/K+-ATPase interacts directly with RalA and RalB. Ral-GTP pull-down assays demonstrated that short-term ouabain treatment of A7r5 cells, a rat aorta smooth muscle cell line, caused activation of Ral GTPase. Maximal activation was observed 10 min after ouabain treatment. Ouabain-mediated Ral activation was inhibited upon the stimulation of Na+/K+-ATPase activity by Ang II. We propose that Ral GTPase is involved in the signal transducing function of Na+/K+-ATPase and provides a possible molecular mechanism connecting Ral to cardiac hypertrophy during diseased conditions.

Fibronectin enhances in vitro vascular calcification by promoting osteoblastic differentiation of vascular smooth muscle cells via ERK pathway

The process of vascular calcification presents several features similar to osteogenesis in which fibronectin (FN) acts as a regulator of osteoblastic differentiation and the ERK signal pathway is involved. In order to find whether FN promotes the osteoblastic differentiation of vascular smooth muscle cells (VSMCs) through the ERK signal pathway, we investigated the effect of FN on the calcification of VSMCs by using an in vitro cell model. VSMCs cultured in plates with FN (0-20 microg/cm2) coating were induced to calcify by 10 mM sodium beta-glycerophosphate (beta-GP). FN exacerbated VSMC calcification in a dose- and time-dependent manner, as indicated by the number of calcifying nodules per slide and the amount of calcium in the deposition. Data from RT-PCR and immunoblotting assay revealed that FN also enhanced the expression of several phenotypic markers of osteoblasts, including alkaline phosphatase (ALP) activity, osteocalcin (OC), and Osf2/Cbfa1, a key transcription factor in osteoblastic differentiation. Furthermore, a specific inhibitor for ERK, PD98059 (10 microM), significantly suppressed the effect of FN on calcification and phenotypic marker expression. These findings seem to suggest that FN enhanced vascular calcification by promoting the osteoblastic differentiation of VSMCs via ERK signal pathway.

Cholestane-3β, 5α, 6β-triol promotes vascular smooth muscle cells calcification

Oxysterols found in atherosclerotic plaque may be associated with vascular calcification. We investigated the effect of oxysterol cholestane-3beta, 5alpha, 6beta-triol (Triol) on in vitro calcification of rat vascular smooth muscle cells (VSMCs). In vitro calcification was induced by incubation of VSMCs with beta-glycerophosphate. Calcifying nodule formation, calcium deposition in extracellular matrix, and alkaline phosphatase (ALP) activity were measured as indices of calcification. Because apoptotic bodies can serve as nucleation sites for calcification, apoptosis of calcifying VSMCs was determined by Hoechst 33258 staining, TUNEL, and FITC-labeled annexin V/PI double staining. The calcium deposition and ALP activity in calcifying VSMCs were much higher than those in non-calcifying VSMCs. Triol increased calcifying nodule formation, calcium deposition, ALP activity, and apoptosis of nodular cells in calcifying VSMCs. As determined by 2,7-dichlorofluorescein fluorescence, Triol induced the generation of reactive oxygen species (ROS) in calcifying VSMCs dose- and time-dependently. Triol-induced increases in calcium deposition, ALP activity, apoptosis, and ROS generation were all attenuated by antioxidant vitamin C plus vitamin E (VC + VE). The results demonstrated that Triol promoted VSMCs calcification through direct increase of ALP activity and apoptosis, probably by ROS-related mechanism.

Angiotensin II directly stimulates activity and alters the phosphorylation of Na-K-ATPase in rat proximal tubule with a rapid time course

We present evidence that Na-K-ATPase in the rat proximal tubule is directly activated by ANG II much faster than previously observed. Specifically, we show that a 2-min exposure to 0.1 and 1 nM ANG II slowed the rate of intracellular sodium accumulation in response to an increase in extracellular sodium added in the presence of gramicidin D. From these data, we show that ANG II directly stimulates Na-K-ATPase activity at rate-limiting concentrations of intracellular sodium. Under these same conditions, exposing proximal tubules to ANG II altered the amount of 32P incorporated into multiple phosphopeptides generated from a tryptic digest of the alpha-subunit of Na-K-ATPase. Na-K-ATPase was isolated from whole cell lysates by means of a ouabain-affinity column and then separated into its individual subunits by SDS-PAGE. Na-K-ATPase bound to the column in its E2 conformation and was eluted by altering its conformation to E1 using Na+ATP. Na-K-ATPase isolated from cells treated with ANG II eluted more easily from the ouabain-affinity column than Na-K-ATPase isolated from control cells, suggesting that ANG II decreased the affinity of Na-K-ATPase for ouabain. Thus ANG II rapidly stimulated the activity of Na-K-ATPase in 2 min or less by a mechanism that could involve changes in phosphorylation and conformation of Na-K-ATPase. We suggest that the physiological role for rapid direct activation of Na-K-ATPase is greater control of intracellular sodium during sodium reabsorption.

Inhibition of Intimal Thickening in the Rat Carotid Artery Injury Model by a Nontoxic Ras Inhibitor

BACKGROUND

Neointimal formation with and without previous vascular injury is common after balloon dilation and in transplant arteriosclerosis. It involves proliferation and migration of medial smooth muscle cells and inflammation, processes that are regulated by Ras proteins and their down-stream effectors. Farnesylthiosalicylate (FTS) is a Ras inhibitor that interferes with Ras membrane anchorage and affects Ras proteins in their active state. In the present study, we tested the hypothesis that systemic administration of FTS will suppress intimal thickening in the rat carotid injury model.

METHODS AND RESULTS

The effects of FTS on rat vascular smooth muscle cells (VSMC) and splenocytes proliferation were evaluated in vitro. The in vivo effects of FTS on the neointima of balloon-injured male Wistar rats, treated daily for 2 weeks with FTS (5 mg/kg weight, intraperitoneally) were evaluated by determination of Ras, Ras-GTP, and active ERK levels (3 days after injury), and by quantitative determination of the extent of intimal thickening and immunohistochemistry for Ras, iNOS, NFkB, and Ki-67 (2 weeks after injury). FTS inhibited VSMC and splenocyte proliferation as well as interferon-gamma secretion by splenocytes in a dose-dependent manner. Compared with controls, FTS treatment resulted in a strong decrease in Ras-GTP and active ERK, and it significantly reduced intimal thickening after the injury. Ras expression appeared predominantly at areas of neointima regardless of the treatment group. NFkB and iNOS-positive cell numbers were reduced in sections of FTS treated rats.

CONCLUSIONS

FTS appears to act as a potent inhibitor of intimal thickening in a model of experimental arterial injury.

Bradykinin B(1) receptor mediates inhibition of neointima formation in rat artery after balloon angioplasty

We evaluated the effects of the kallikrein-kinin system on the proliferation and migration of primary cultured vascular smooth muscle cells (VSMCs) in vitro and neointima formation in balloon-injured rat carotid arteries in vivo. In cultured rat VSMCs, tissue kallikrein inhibited cell proliferation, and this inhibitory effect was blocked by Sar-Tyr-Aca(epsilon)-Lys [D-betaNal(7), Ile(8)]-des-Arg(9)-bradykinin, a bradykinin B(1) receptor antagonist, and by icatibant, a bradykinin B(2) receptor antagonist. Platelet-derived growth factor significantly increased the expression of the B(1) receptor but not the B(2) receptor in VSMCs. Platelet-derived growth factor-induced cell migration was significantly attenuated by des-Arg(9)-bradykinin and to a lesser degree by bradykinin. Endogenous B(1) receptor mRNA increased in rat carotid arteries after balloon angioplasty. After local delivery of adenovirus carrying the human tissue kallikrein gene into the rat carotid artery, we observed a 54% reduction in the intima/media ratio at the injured site compared with the control ratio (n=7, P:<0.01). Administration of the B(1) receptor antagonist via minipumps blocked the protective effect of kallikrein and partially reversed the intima/media ratio toward the control ratio. Kallikrein gene delivery results in the regeneration of endothelium compared with the control groups, and the B(1) receptor antagonist abolished this effect. Nitrite/nitrate, cGMP, and cAMP levels in balloon-injured arteries significantly increased after kallikrein gene delivery, whereas the B(1) receptor antagonist abolished these increases (n=4 or 5, P:<0.05). These results indicate that the B(1) receptor contributes to the reduction of neointima formation via the promotion of reendothelialization and inhibition of VSMC proliferation and migration through NO-cGMP and cAMP signaling pathways. This study provides significant implications in treating restenosis after revascularization.

Kallistatin stimulates vascular smooth muscle cell proliferation and migration in vitro and neointima formation in balloon-injured rat artery

Kallistatin, a serine proteinase inhibitor (serpin), is expressed in the endothelial and smooth muscle cells of blood vessels. The potential function of kallistatin in vascular biology was investigated by studying its role in the proliferation and migration of cultured primary aortic vascular smooth muscle cells (VSMCs) in vitro and in neointima formation in rat artery after balloon angioplasty in vivo. Exogenous kallistatin induced a >2-fold increase of VSMC proliferation and cell growth as measured by [(3)H]thymidine incorporation and cell counts and a 2.3-fold increase of cell migration in modified Boyden chambers. In balloon-injured vessels, endogenous kallistatin mRNA and protein levels increased up to 10-fold as determined by competitive polymerase chain reaction and by ELISA. Intense staining of kallistatin mRNA was identified in the proliferating VSMCs of balloon-injured arteries during cell migration from media to neointima by in situ hybridization histochemistry and immunohistochemistry. We observed an induction of kallistatin expression by platelet-derived growth factor (PDGF) and upregulation of p42/44 mitogen-activated protein kinase (MAPK) activity by kallistatin in cultured VSMCs. Conversely, adenovirus-mediated transfer of kallistatin antisense cDNA into cultured VSMCs inhibited PDGF-induced p42/44 MAPK activity and cell proliferation. Furthermore, local delivery of adenovirus carrying kallistatin antisense cDNA significantly downregulated kallistatin mRNA levels and attenuated neointima formation in balloon-injured rat arteries in vivo. These results indicate that kallistatin may play an important role in mediating PDGF-induced MAPK pathway on VSMC proliferation and in neointima formation after balloon angioplasty.

ANF elicits phosphorylation of the cGMP phosphodiesterase in vascular smooth muscle cells

Guanosine 3',5'-cyclic monophosphate (cGMP)-binding, cGMP-specific phosphodiesterase (PDE5) is abundant in vascular smooth muscle, and this enzyme is a potent substrate for cGMP-dependent protein kinase (PKG) in vitro. Binding of cGMP to the allosteric sites of PDE5 is required for this phosphorylation to occur. Vascular smooth muscle cells (VSMC) were used to determine if PDE5 is phosphorylated in intact cells when cGMP is increased. With the use of anti-PDE5 antibodies, a phosphorylated 93-kDa protein band was immunoprecipitated from early passaged primary cultures of VSMC that had been preincubated with 32(Pi) to label cellular ATP and then treated with atrial natriuretic factor (ANF). In the absence of ANF, there was no detectable incorporation of radiolabeled phosphate into this band. Phosphorylation of the 93-kDa protein was augmented by pretreating cells with 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP) to activate PKG before addition of ANF. 8-BrcGMP, which interacts poorly with the allosteric sites of PDE5, had no effect on PDE5 phosphorylation in the absence of ANF. Phosphorylation of PDE5 in response to treatment of cells with ANF was associated with a two- to fourfold increase in PDE activity in immunoprecipitates. Multiple-passaged VSMC, which are deficient in PKG but retain PDE5, demonstrated no ANF-dependent increase in phosphorylation or catalytic activity of PDE5. However, incubation of immunoprecipitated PDE5 from these cells with purified PKG, cGMP, and a phosphorylation mixture containing [gamma-32P]ATP resulted in 32(Pi) incorporation into PDE5 that was correlated with increased catalytic activity. These studies are the first to demonstrate phosphorylation of PDE5 in intact cells, thus suggesting a physiological role for this enzyme in smooth muscle regulation.

Cyclosporine A-induced contraction of isolated rat aortic smooth muscle cells

The mechanisms by which the immunosuppressive drug cyclosporine A (CsA) induces hypertension and nephrotoxicity are still not fully understood. Although smooth muscle cell (SMC) contraction is probably the mechanism of vasoconstriction, the direct contractive effect of CsA on SMCs has not yet been demonstrated. Thus, it was the purpose of this study to evaluate the direct effects of CsA in cultured SMCs through interactive image analysis. In aortic SMCs, CsA at the concentrations of 0.01, 0.1 and 1 microM, caused a concentration-dependent decrease of the planar cross-sectional area (PCSA) after 30 min and 60 min of treatment. The PCSA decreases were statistically significantly different from control at all concentrations. No cytotoxicity was observed under these conditions. Ten minutes preincubation of SMCs with a monoclonal antibody against endothelin-1 (ET-1) significantly prevented the CsA effects at 1 microM. When the same antibody was heat inactivated or an unspecific antibody (anti-desmin immunoglobulin G) was applied, the CsA-induced contractions were not affected. These data suggest that CsA can cause a direct contractive effect on vascular SMCs. This effect is partly mediated by ET-1.

Differential effect of hydrogen peroxide and superoxide anion on apoptosis and proliferation of vascular smooth muscle cells

BACKGROUND

Proliferation and apoptosis of vascular smooth muscle cells (VSMCs) are two important components of atherosclerosis, restenosis, and hypertension. Although reactive oxygen species have been demonstrated to participate in the pathogenesis of these diseases, their precise involvement has not been fully understood. We hypothesized that different reactive oxygen species exert distinct effects on proliferation and apoptosis of VSMCs.

METHODS AND RESULTS

Cultured rat VSMCs were exposed to xanthine oxidase/xanthine (XO/X) or H2O2-Fe(II). A single exposure to XO/X predominantly resulted in cell proliferation, whereas frequent exposures to high levels of XO/X predominantly resulted in cell death. Administration of superoxide dismutase and catalase revealed that O2- but not H2O2, was mitogenic to VSMCs, whereas H2O2 was responsible for VSMC death. Treatment with H2O2-Fe(II) alone or in the presence of different hydroxyl radical scavengers showed that VSMC death occurred in a dose-dependent manner and was mediated by the formation of hydroxyl radicals. Cell death caused by XO/X or H2O2-Fe(II) occurred by apoptosis as revealed by condensation of nuclei, appearance of a "DNA ladder," increases in DNA fragmentation, and positive in situ nick-end labeling. Northern blot analysis indicated that bcl-2 and c-fos but not p53 and c-myc may participate in mediating H2O2-Fe(II)-induced VSMC apoptosis.

CONCLUSIONS

Different reactive oxygen species exert distinct effects on VSMCs, with O2- inducing proliferation and H2O2 causing apoptosis. Thus, reactive oxygen species might participate in atherosclerosis, restenosis, and hypertension in a dual manner by stimulating proliferation and triggering apoptosis of VSMCs.

Smooth muscle cell expression of type I cyclic GMP-dependent protein kinase is suppressed by continuous exposure to nitrovasodilators, theophylline, cyclic GMP, and cyclic AMP

A key component of the nitric oxide-cyclic guanosine monophosphate (cGMP) pathway in smooth muscle cells (SMC) is the type I GMP-dependent protein kinase (PK-G I). Activation of PK-G I mediates the reduction of cytoplasmic calcium concentrations and vasorelaxation. In this manuscript, we demonstrate that continuous exposure of SMC in culture to the nitrovasodilators S-nitroso-N-acetylpenicillamine (SNAP) or sodium nitroprusside (SNP) results in approximately 75% suppression of PK-G I mRNA by 48 h. PK-G I mRNA and protein were also suppressed by continuous exposure to cGMP analogues 8-bromo- and 8-(4-chlorophenylthio) guanosine-3,5-monophosphate or the cAMP analogue dibutyryl cAMP. These results suggest that activation of one or both of the cyclic nucleotide-dependent protein kinases mediates PK-G I mRNA suppression. Using isoform-specific cDNA probes, only the PK-G I alpha was detected in SMC, either at baseline or after suppression, while PK-G I beta was not detected, indicating that isoform switch was not contributing to the gene regulation. Using the transcription inhibitor actinomycin D, the PK-G I mRNA half-life in bovine SMC was observed to be 5 h. The half-life was not affected by the addition of SNAP to actinomycin D, indicating no effect on PK-G I mRNA stability. Nuclear runoff studies indicated a suppression of PK-G I gene transcription by SNAP. PK-G I suppression was also observed in vivo in rats given isosorbide dinitrate in the drinking water, with a dose-dependent suppression of PK-G I protein in the aorta. PK-G I antigen in whole rat lung extract was also suppressed by administration of isosorbide or theophylline in the drinking water. These data may contribute to our understanding of nitrovasodilator resistance, a phenomenon resulting from continuous exposure to nitroglycerin or other nitrovasodilators.

Responsiveness to growth factors in aortic vascular smooth muscle cells from rats with cirrhosis

Hemodynamic changes in cirrhosis may be associated with alterations in aortic vascular smooth muscle cell (AVSMC) function. The present study compared the proliferative response to serum and growth factors in cirrhotic and control AVSMC. Serum from cirrhotic rats, cirrhotic cell lysates, and the conditioned medium of cultured cirrhotic AVSMC induced an increase in [3H]thymidine incorporation in control but not in cirrhotic AVSMC. Platelet-derived growth factor-beta (PDGF-BB) induced a greater increase in [3H]thymidine incorporation in cirrhotic than in control cells. [3H]thymidine incorporation induced by cirrhotic conditioned medium was blocked by anti-PDGF antibody. Immunoblot studies showed that the anti-PDGF antibody recognized a 30-kDa protein in the conditioned medium of cirrhotic AVSMC culture, a protein corresponding to PDGF. Binding studies of PDGF-BB indicated a twofold increase in receptor density in cirrhotic AVSMC with no alteration in affinity for PDGF-BB. We conclude that an increased responsiveness of cirrhotic AVSMC to the PDGF could contribute to alterations in AVSMC and muscle cell tone that may play a role in the hemodynamic changes in cirrhosis.

Extracellular ATP increases cytosolic calcium in cultured rat renal arterial smooth muscle cells

1. Experiments were conducted on cultured renal arterial smooth muscle cells to determine the ability of extracellular ATP to alter cytosolic calcium concentration and to determine the mechanisms by which this effect occurs. 2. ATP (100 mumol/L) caused the fluorescence ratio of fura-2 to increase from a control value of 1.06 +/- 0.05 to 2.06 +/- 0.13 (P < 0.01) before stabilizing at a sustained level of 1.35 +/- 0.04 (n = 8; P < 0.05). 3. Removal of extracellular calcium from the bathing medium resulted in an attenuation of the initial response to 100 mumol/L ATP with cell fluorescence increasing from 1.16 +/- 0.18 to 1.44 +/- 0.18 ratio units (n = 5). Furthermore, the initial increase in fluorescence ratio rapidly declined to 1.02 +/- 0.06, indicating that an influx of extracellular calcium is required to sustain the increase in fura-2 fluorescence. 4. Depletion of intracellular calcium pools with thapsigargin prevented the increase in fura-2 fluorescence evoked by ATP. 5. These data suggest that ATP-mediated increases in cytosolic calcium in cultured renal arterial smooth muscle cells involve calcium release from the thapsigargin-sensitive, intracellular pool in conjunction with calcium influx from the extracellular medium.

Angiotensin II and angiotensin-(1-7) effects on free cytosolic sodium, intracellular pH, and the Na(+)-H+ antiporter in vascular smooth muscle

The aim of the present study was to define the effects of angiotensin II (Ang II) and Ang-(1-7) on free cytosolic Na+ (Na+i), intracellular pH (pHi), and the Na(+)-H+ antiporter in cultured vascular smooth muscle cells from rat aorta. Cells were loaded with either BCECF-AM or SBFI-AM for measurement of pHi and Na+i, respectively. Ang II (10(-6) mol/L) caused a rapid rise in Na+i followed by a progressive increase that peaked at about 10 minutes (from 11 +/- 1.5 to 16 +/- 1.5 mmol/L, P < .001), whereas Ang-(1-7) (10(-6) mol/L) did not affect Na+i significantly (from 11.5 +/- 1.1 to 11.8 +/- 0.07 mmol/L). The effect of Ang II on Na+i was concentration dependent (delta Na+i, 5.1 +/- 0.9, 3.8 +/- 0.6, 1.6 +/- 0.6, and 0.14 +/- 0.18 mmol/L with decreasing concentrations of 10(-6), 10(-7), 10(-8), and 10(-9) mol/L, respectively). Ang II caused a brief acidification followed by an increase in pHi (from 7.34 +/- 0.03 to 7.43 +/- 0.03 after 10 minutes, P < .005), and Ang-(1-7) had no significant effect on pHi (from 7.23 +/- 0.03 to 7.23 +/- 0.03). To investigate whether pHi and Na+i changes induced by Ang II were due to cell Na+ entry via stimulation of the Na(+)-H+ antiporter, we pretreated cells with EIPA (25 mumol/L) or ouabain (2.0 mmol/L). Ang II in the presence of ouabain caused a greater increase than that seen with ouabain alone (delta Na+i, 13 +/- 1.5 versus 6.3 +/- 1.2 mmol/L, P < .0025). EIPA by itself decreased Na+i and pHi. After EIPA, Ang II failed to increase both Na+i and pHi, demonstrating that the Na(+)-H+ antiporter is responsible for the rises in Na+i and pHi during stimulation with Ang II. To further characterize the mechanism of Ang II action, we exposed cells to an Ang II type I receptor antagonist (L-158,809, 10(-6) mol/L) or two different type 2 receptor antagonists (PD 123177 and CGP 421112A, 10(-6) mol/L). L-158,809 completely blocked the rise in pHi caused by Ang II, whereas PD 123177 and CGP 421112A did not. We conclude that Ang II increases both Na+i and pHi, and both effects are mediated by stimulation of the Na(+)-H+ antiporter. Ang-(1-7), by contrast, has no significant effect on Na+i, pHi, or the Na(+)-H+ antiporter. Stimulation of this antiporter by Ang II is exerted through the type 1 receptor.

VEGF165 expressed by a replication-deficient recombinant adenovirus vector induces angiogenesis in vivo

To evaluate the concept that localized delivery of angiogenic factors via virus-mediated gene transfer may be useful in the treatment of ischemic disorders, the replication-deficient adenovirus (Ad) vector AdCMV.VEGF165 (where CMV is cytomegalovirus and VEGF is vascular endothelial growth factor) containing the cDNA for human VEGF165, a secreted endothelial cell-specific angiogenic growth factor, was constructed. Human umbilical vein endothelial cells (HUVECs) and rat aorta smooth muscle cells (RASMCs) infected with AdCMV.VEGF165 (5 and 20 plaque-forming units [pfu] per cell) demonstrated VEGF mRNA expression and protein secretion into the supernatant. Furthermore, the conditioned medium from these cells enhanced vascular permeability in vivo. In contrast, neither VEGF mRNA nor secreted protein was found in uninfected HUVECs or RASMCs or in cells infected with the control vector AdCMV.beta gal (where beta gal is beta-galactosidase). Assessment of starved HUVECs at 14 days demonstrated sixfold more cells for AdCMV.VEGF165-infected HUVECs (20 pfu per cell) than for either infected or uninfected control cells. RASMC proliferation was unaffected by infection with AdCMV.VEGF165. When plated in 2% serum on dishes precoated with reconstituted basement membrane (Matrigel), HUVECs infected with AdCMV.VEGF165 (20 pfu per cell) differentiated into capillary-like structures. Under similar conditions, both uninfected HUVECs and HUVECs infected with AdCMV.beta gal did not differentiate. To evaluate the ability of AdCMV.VEGF165 to function in vivo, either AdCMV. VEGF165 or AdCMV.beta gal (2 x 10(10) pfu) was resuspended in 0.5 mL Matrigel and injected subcutaneously into mice. Immunohistochemical staining demonstrated VEGF in the tissues surrounding the Matrigel plugs containing AdCMV.VEGF165 up to 3 weeks after injection, whereas no VEGF was found in the control plugs with AdCMV.beta gal. Two weeks after injection, there was histological evidence of neovascularization in the tissues surrounding the Matrigel containing AdCMV.VEGF165, whereas no significant angiogenesis was observed in response to AdCMV.beta gal. Furthermore, the Matrigel plugs with AdCMV.VEGF165 demonstrated hemoglobin content fourfold higher than the plugs with AdCMV.beta gal. Together, these in vitro and in vivo studies are consistent with the concept that Ad vectors may provide a useful strategy for efficient local delivery of VEGF165 in the treatment of ischemic diseases.

Vascular smooth muscle cells metabolize endothelin-1 in the absence of a functional receptor

Endothelin-1 (ET-1), a 21 amino acid vasoconstrictor peptide synthesized by vascular endothelial cells, exerts powerful actions on the underlying smooth muscle cells. The receptor and signal transduction mechanisms for ET-1 have been well characterized in rat aortic A10 vascular smooth muscle cells (A10VSMC). This investigation has characterized the internalization and metabolism of [125I]ET-1 by A10VSMC. A10VSMC internalized [125I]ET-1 rapidly in a receptor-mediated manner. However, inhibition of the binding/internalization had no effect on the metabolism of [125I]ET-1 by these cells. Thus, the presence of excess unlabeled ET-1 in the incubation, treatment of the cells with ET receptor antagonists, and homologous ligand-induced down-regulation of the ET-1 receptor all inhibited binding and internalization of [125I]ET-1 by A10VSMC, but not its metabolism. Furthermore, addition of excess unlabeled ET-1 to the incubations containing cells pretreated with the homologous ligand (receptor down-regulated cells) also failed to inhibit the metabolism of [125I]ET-1. Essentially similar characteristics of [125I]ET-1 binding and metabolism were exhibited by primary cultures of smooth muscle cells derived from rat thoracic aorta. Such ability of the vascular smooth muscle cells to degrade ET-1, which is produced constitutively by the endothelial cells, presents a novel mechanism in the regulation of its local and circulating concentration.

Intracellular signaling pathways required for rat vascular smooth muscle cell migration. Interactions between basic fibroblast growth factor and platelet-derived growth factor

Intracellular signaling pathways activated by both PDGF and basic fibroblast growth factor (bFGF) have been implicated in the migration of vascular smooth muscle cells (VSMC), a key step in the pathogenesis of many vascular diseases. We demonstrate here that, while bFGF is a weak chemoattractant for VSMCs, it is required for the PDGF-directed migration of VSMCs and the activation of calcium/calmodulin-dependent protein kinase II (CamKinase II), an intracellular event that we have previously shown to be important in the regulation of VSMC migration. Neutralizing antibodies to bFGF caused a dramatic reduction in the size of the intracellular calcium transient normally seen after PDGF stimulation and inhibited both PDGF-directed VSMC migration and CamKinase II activation. Partially restoring the calcium transient with ionomycin restored migration and CamKinase II activation as did the forced expression of a mutant CamKinase II that had been "locked" in the active state by site-directed mutagenesis. These results suggest that bFGF links PDGF receptor stimulation to changes in intracellular calcium and CamKinase II activation, reinforcing the central role played by CamKinase II in regulating VSMC migration.

Regulation of intracellular pH in the smooth muscle of guinea-pig ureter: Na+ dependence

1. Mechanisms involved in the regulation of intracellular pH (pHi) in smooth muscle cells of guinea-pig ureter have been investigated using double-barrelled pH-sensitive microelectrodes in isolated strips of tissue. 2. Removal of CO2-HCO3- from the superfusing solution caused a fall in the steady-state pHi except in a few cells which had been excised from the animal for many hours (usually > 24 h). The pHi value was 7.22 +/- 0.09 (n = 89; mean +/- S.D. of an observation) in solution buffered with 5% CO2-21 mM HCO3-, compared with 6.92 +/- 0.24 (n = 67) in the nominal absence of CO2-HCO3-. Recovery from experimentally induced acidosis was faster in the presence, rather than nominal absence, of CO2-HCO3- (mean half-times of 2.7 +/- 0.7 min, n = 41, and 4.6 +/- 1.3 min, n = 12, respectively). These results suggest the presence of both HCO(3-)-dependent and -independent mechanisms for the effective extrusion of acid equivalents. 3. Recovery from acidosis was dependent on external Na+ (Na+o) in both the presence and nominal absence of CO2-HCO3-, with an apparent half-maximal activation at approximately 4 and 20 mM Na+o, respectively. Removal of Na+o in the steady state caused a fall in pHi which proceeded at a faster rate in the presence rather than in the nominal absence of CO2-HCO3-. 4. Amiloride (100 microM-1 mM) reversibly inhibited the recovery from acidosis and caused a fall in the steady-state pHi when applied in the nominal absence of CO2-HCO3-, but had no measurable effect on either the recovery from acidosis or steady-state pHi in the presence of CO2-HCO3-. These results suggest that Na(+)-H+ exchange was responsible for extrusion of acid equivalents in the nominal absence of CO2 and HCO3-, but that it played little part under more physiological conditions. 5. Although Na(+)-H+ exchange appeared to be activated below a pHi of about 7.2, it was incapable of maintaining a 'normal' pHi in the nominal absence of CO2-HCO3- in freshly excised cells, where values between 6.06 and 6.89 were recorded. Only in aged preparations, in which the intrinsic intracellular acid loading was substantially reduced (as judged from the rate of acidification on application of amiloride in the nominal absence of CO2-HCO3-) did the steady-state value approximate to that observed in the presence of CO2-HCO3-, at about 7.2.

High-affinity binding and localization of the cyclic GMP-dependent protein kinase with the intermediate filament protein vimentin

The major receptor protein for cyclic GMP (cGMP) in smooth muscle is the cGMP-dependent protein kinase (cGMP kinase). The more abundant I alpha isoform (subunit M(r) congruent to 78,000) of this enzyme mediates the effects of cGMP to relax contracted vascular smooth muscle preparations. In this study, we have addressed the hypothesis that the cGMP kinase is anchored to intracellular proteins which might serve to target cGMP kinase to protein substrates. Using a gel overlay technique, immunoprecipitation, and a fluorescence binding assay for cGMP kinase, we have identified vimentin as a high-affinity and specific binding protein for cGMP kinase. Binding of cGMP kinase to vimentin is reversible and stoichiometric (one cGMP kinase dimer/vimentin dimer) with a KD of approximately 49 nM. The site of high-affinity binding between cGMP kinase and vimentin did not appear to be localized to the catalytic domain of the kinase since vimentin phosphorylated by cGMP kinase and peptide substrates for cGMP kinase did not compete for high-affinity binding. Neither the proteolytically-derived 69-kDa catalytic fragment nor the 8-kDa N-terminal fragment bound vimentin with high affinity, suggesting that the cGMP kinase dimer was necessary for the interaction. Vimentin was readily phosphorylated in vitro with the dimer, but not the monomeric 69-kDa catalytic fragment even though the monomeric 69-kDa fragment was catalytically active toward other substrates such as histone F2b and peptides. This suggests that the high-affinity interaction between cGMP kinase and vimentin occurs at the N-terminal region, thus allowing the interaction between the phosphorylation site of vimentin and the catalytic site of cGMP kinase to occur.(ABSTRACT TRUNCATED AT 250 WORDS)

Migration of cultured vascular smooth muscle cells through a basement membrane barrier requires type IV collagenase activity and is inhibited by cellular differentiation

The migration of vascular smooth muscle cells (VSMCs) from the tunica media to the neointima is a key event in the development and progression of many vascular diseases and a highly predictable consequence of mechanical injury to the blood vessel. In vivo, VSMCs are surrounded by and embedded in a variety of extracellular matrices (ECMs) that must be traversed during migration. One of the principal barriers to cell movement in the intact vessel is the basement membrane (BM) that surrounds each VSMC and separates the VSMC-containing medial cell layer from the endothelium. We have used a Boyden chamber to monitor the ability of VSMCs to degrade a BM barrier as they migrate toward a chemoattractant and to define the role of extracellular proteases in this process. We show that cultured VSMCs can migrate across a BM barrier and that this ability was dependent on the phenotypic state of the cell. VSMCs maintained in a proliferating or "synthetic" state readily migrated across a BM toward a chemoattractant, whereas the migration of serum-starved/differentiated VSMCs was suppressed by > 80% (P < .001). By use of a number of peptides that inhibit matrix metalloproteinase (MMP) activity, the migration of proliferating VSMCs across the BM barrier was inhibited by > 80% (P < .0001), whereas migration that occurred in the absence of the barrier was unaffected. Northern blotting and zymographic analyses indicated that 72-kD type IV collagenase (MMP2) was the principal MMP expressed and secreted by these cells. Accordingly, antisera capable of selectively neutralizing MMP2 activity also inhibited VSMC migration across the barrier without significantly affecting the migration of VSMCs in the absence of the barrier. Finally, MMP2 activity was also regulated by the phenotypic state of the cells in that MMP2 activity expressed by serum-starved/differentiated VSMCs was < 5% of that measured in proliferating VSMCs. Extrapolating to the in vivo situation in which VSMCs reside in an ECM composed of various BM barriers, these results suggest that VSMC migration in vivo may be dependent on MMP2 activity. That activity, in turn, could be regulated by the phenotypic state of VSMCs and increase as these cells undergo the transition from a quiescent and differentiated state to that of a dedifferentiated, proliferating, and motile phenotype after injury to the vessel.

Alpha 1 adrenergic receptor-induced c-fos gene expression in rat aorta and cultured vascular smooth muscle cells

While growth of blood vessels is important in hypertension, relatively little is known about the contribution of catecholamines. Using isolated rat aorta and cultured smooth muscle cells, we examined adrenergic stimulation of gene expression. Phenylephrine, a selective alpha 1 adrenergic receptor agonist, caused a rapid and transient increase in c-fos mRNA accumulation which was inhibited by prazosin, an alpha 1 receptor antagonist. Similarly, phenylephrine stimulated c-jun and c-myc mRNA accumulation. Chloroethyl-clonidine, a compound which irreversibly blocks alpha 1B receptors, completely blocked the phenylephrine-induced increase in c-fos mRNA. RNase protection experiments demonstrated that rat aorta prominently expressed mRNA for alpha 1B and alpha 1A/D receptors. Phenylephrine-induced c-fos mRNA was partially inhibited by H-7, a protein kinase C inhibitor, and by nifedipine, a Ca2+ channel blocker; these two compounds together had additive effects. In situ hybridization showed that expression of c-fos mRNA induced by phenylephrine was localized to aorta's medial layer. These results suggest that alpha 1 receptor-induced increase in c-fos mRNA in aorta is mediated by a chloroethyl-clonidine-sensitive receptor subtype signaling via increasing intracellular Ca2+ concentrations and activating protein kinase C.

Effect of subthreshold ouabain on the tone of guinea-pig aortic strips following repeated noradrenaline stimulation

1. The effect of ouabain at a concentration (0.8 microM) that does not induce contractile response in guinea-pig aortic strips has been studied on endothelium-denuded strips repeatedly stimulated with 1 microM noradrenaline or 60 mM K+ applied for 5 min every 30 min. 2. The resting tone (i.e. the tone between one noradrenaline stimulation and the following) of the aortic strips exposed to ouabain increased progressively, whereas the control strips (no ouabain) completely relaxed on washout of the agonist. In the aortic strips stimulated by 60 mM K+, the resting tone did not increase. 3. The calcium antagonist, verapamil, did not affect the increase in tone, that was nevertheless strictly dependent on external calcium, since the contracted strips completely relaxed on calcium removal and promptly contracted again on calcium readdition. This finding indicates a mechanism independent of voltage-gated calcium channels. 4. Caffeine-induced contractions, taken as a measure of sarcoplasmic reticulum calcium content, were amplified by the presence of ouabain in aortic strips either stimulated by noradrenaline or unstimulated, with a larger increase in the former. 5. These results suggest that the repeated stimulation of guinea-pig aortic strips by noradrenaline in the presence of ouabain, by raising both intracellular Na+ and Ca2+, decreases the ouabain threshold concentration required for contraction, thus increasing the responsiveness of vascular smooth muscle to the glycoside.

Altered signal transduction in vascular smooth muscle cells of spontaneously hypertensive rats

The hypothesis that signal transduction mediated by platelet-derived growth factor (PDGF) and angiotensin II (Ang II) is altered in vascular smooth muscle (VSM) cells from the spontaneously hypertensive rat (SHR) was tested by measuring changes in the cytosolic free calcium concentration ([Ca2+]i). [Ca2+]i was measured in cultured aortic smooth muscle cells from SHRs and Wistar-Kyoto (WKY) normotensive rats using fura-2 as a calcium indicator and a microscopic digital image analysis system. Activation of cells with Ang II resulted in a prompt though transient rise in [Ca2+]i; the maximum increase was observed after 10-30-second intervals. On the other hand, activation of cells with PDGF BB produced an increase in [Ca2+]i with a 40-60-second lag period; the maximum increase was observed 2-4 minutes after the addition of PDGF. PDGF-stimulated increases in [Ca2+]i were markedly inhibited by the addition of the calcium channel antagonist verapamil (100 microM) as well as by removal of calcium from the extracellular bathing medium. However, Ang II-stimulated [Ca2+]i was not significantly affected by the addition of verapamil or by removal of extracellular calcium. These results would indicate that PDGF-mediated increases in [Ca2+]i in VSM cells are predominantly via Ca2+ influx, whereas Ang II-mediated increases are due to calcium release from intracellular pools. Basal and PDGF- and Ang II-stimulated increases in [Ca2+]i were significantly greater (p less than 0.05) in SHR VSM cells compared with WKY cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelin inhibits the atrial natriuretic factor stimulated cGMP production by activating the protein kinase C in rat aortic smooth muscle cells

Preincubation of rat thoracic aortic smooth muscle cells with endothelin inhibits the atrial natriuretic factor (ANF)-induced cGMP accumulation in these cells in a concentration dependent manner. The maximal inhibition of 64% was afforded by 1 x 10(-6) M endothelin and the half maximal inhibition (IC50) was achieved with 1 x 10(-9) M endothelin. Endothelin (1 x 10(-6) M) also increased the plasma membrane bound protein kinase C (PKC) activity by 4 fold. Hormone-dependent increase in PKC activity was limited to plasma membranes only and some decrease in cytosolic PKC activity was observed. However, phorbol 12-myristate 13-acetate (PMA) (1 x 10(-6)M) provoked a total loss of cytosolic PKC activity and a net gain in membranous PKC activity indicative of the translocation of the enzyme. Pretreatment of these cells with H-7, a PKC inhibitor, released the endothelin and PMA-mediated attenuation of ANF-stimulated cGMP formation. These results suggest that PKC is involved in the regulation of ANF-induced cGMP accumulation and that the vasoconstrictor activity of endothelin might involve inhibition of the vasorelaxant activity of ANF through the inhibition of cGMP accumulation in smooth muscle cells (SMCs) of the rat aorta.

Potentiation of inositol trisphosphate production by dexamethasone

One of the mechanisms of glucocorticoid-induced hypertension has been thought to be the enhancement of vascular responsiveness to vasoconstrictors. In this regard, the effects of glucocorticoids on inositol trisphosphate production in vascular smooth muscle cells were studied. Angiotensin II and arginine vasopressin transiently increased inositol trisphosphate formation in a dose-dependent manner. Pretreatment with dexamethasone for 48 hours shifted the dose-response trisphosphate curves of angiotensin II- and arginine vasopressin-induced inositol trisphosphate production to the left, that is, it significantly reduced the half-maximal effective concentrations of angiotensin II (from 25 nM to 5 nM) and arginine vasopressin (from 50 nM to 25 nM). These effects of dexamethasone required a minimum of 12 hours of incubation; maximum effect was observed after 24 hours of treatment. A glucocorticoid antagonist, RU 38486, completely blocked these effects. To elucidate the interaction with prostaglandin, we used indomethacin, a potent inhibitor of prostaglandin synthesis. Treatment with indomethacin shifted the dose-response curves of angiotensin II- and arginine vasopressin-induced inositol trisphosphate production to the left. However, this shift was less than that seen after dexamethasone treatment. Indomethacin alone did not completely reproduce dexamethasone effects, and no additive effect between indomethacin and dexamethasone was observed. These results suggest, at least in part but not entirely, that the effects of dexamethasone depended on prostaglandin synthesis inhibition. We concluded that glucocorticoids altered the responsiveness of vascular smooth muscle cells to angiotensin II and arginine vasopressin through a glucocorticoid-specific receptor. These actions strongly support the mechanism by which the glucocorticoid induced hypertension through the increased sensitivity to vasoconstrictors.

Impaired response to angiotensin II in type 1 (insulin-dependent) diabetes mellitus. Role of prostaglandins and sodium-lithium countertransport activity

The pathogenesis of diabetic nephropathy remains elusive. A role for renal prostaglandins in antagonizing the hormonal effects of renin-angiotensin II has been postulated as a putative factor leading to hyperfiltration in patients with Type 1 (insulin-dependent) diabetes mellitus. Our aim was to elucidate the effects of angiotensin II on kidney haemodynamics and on blood pressure in eight normal subjects, in nine normotensive, in nine hypertensive with normal sodium-lithium countertransport activity in erythrocytes, in seven hypertensive without and in eight hypertensive Type 1 diabetic patients with microalbuminuria and with high sodium-lithium countertransport activity in erythrocytes. Angiotensin II infusion (4 ng.kg-1.min-1 for 60 min) decreased the glomerular filtration rate to a greater extent in normal subjects (-20%), than in normotensive patients (-5% p less than 0.01), in hypertensive patients with normal sodium-lithium countertransport activity in erythrocytes (-8% p less than 0.01) in hypertensive patients with high sodium-lithium countertransport (-6% p less than 0.01) and in hypertensive microalbuminuric patients (-5% p less than 0.01) with Type 1 diabetes. The urinary excretion rate of vasodilatory prostaglandins was two-three fold higher in all patients than in normal subjects. Acute indomethacin treatment restored a normal response to angiotensin II infusion in normotensive patients, but did not change the renal haemodynamic response in normal subjects. With regard to hypertensive patients with and without microalbuminuria indomethacin treatment restored a normal response to angiotensin II in some but not all patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of inhibition of Na+/K(+)-ATPase on the vasopressin-induced increase in intracellular Na+ concentration in vascular smooth muscle cells

The effect of inhibition of Na+/K(+)-ATPase by ouabain on the arginine vasopressin (AVP)-induced increase in intracellular Na+ concentration [( Na+]i) was examined in cultured rat vascular smooth muscle cells (VSMC) by the direct measurement of [Na+]i using a fluorescent indicator dye. AVP at a concentration of 1 x 10(-9) M or higher increased [Na+]i in a dose-dependent manner in cultured rat VSMC. The preincubation of cells with 1 x 10(-4) M ouabain for 1 hr at 37 degrees C did not affect the basal [Na+]i but enhanced the 1 x 10(-6) M AVP-induced increase in [Na+]i. The preincubation was not necessary because similar results were obtained after the simultaneous administration of AVP and ouabain. The treatment with ouabain did not affect the intracellular pH changes induced by AVP. These results therefore indicate that the inhibition of Na+/K(+)-ATPase enhances the AVP-induced increase in [Na+]i by decreasing cellular Na+ efflux in cultured rat VSMC.

Beta-adrenergic responsiveness in cultured vascular smooth muscle cells and fibroblasts: effect of age

beta-Adrenergic agonists stimulate cyclic 3',5'-adenosine monophosphate (cAMP) accumulation and relaxation in vascular smooth muscle; both of these responses decline in rat aorta with increasing age. To ascertain whether the deficit in beta-receptor stimulated cAMP accumulation persists in isolated aortic smooth muscle cells, the effect of isoproterenol on cAMP accumulation was measured in cultured vascular smooth muscle cells (VSMC) and vascular fibroblasts taken from young (4-6 weeks) and older (8-12 months) Fischer 344 male rats. Immunofluorescent staining confirmed the identity of VSMC as distinct from fibroblasts. Isoproterenol stimulated cAMP accumulation in a time- and concentration-dependent manner in both cell types; maximal cAMP accumulation induced by beta-adrenergic stimulation in cultured cells was much higher than those seen in the intact aorta. While there was a blunting of cAMP response to isoproterenol in fibroblasts cultured from the older rats, the response in VSMC cultured from the older rats was actually increased compared to the VSMC cultured from the younger rats. In contrast, activation of cAMP accumulation in the cultured cells by forskolin was similar in cells from older and young animals. The results suggest that the blunting in isoproterenol-stimulated cAMP accumulation found in aortas from older animals is not seen in VSMC cultured from these animals; whether this change in the culture reflects removal of some extrinsic factor in the older rats or is a consequence of intrinsic changes in the cells in culture requires further investigation.

Inhibition of sodium-calcium and sodium-proton exchangers by amiloride congeners in arterial muscle cells

The inhibitory potencies of several amiloride congeners towards Na(+)-Ca2+ and Na(+)-H+ exchange were compared in rat aortic myocytes. N-(2,4-Dimethylbenzyl)amiloride (DMB) was 10 times more potent towards Na(+)-Ca2+ than Na(+)-H+ exchange. Amiloride and ethylisopropylamiloride were about 5,000 and 10,000 times more potent toward Na(+)-H+ than Na(+)-Ca2+ exchange respectively. N-(3,4-Dichlorobenzyl)amiloride was almost equipotent towards both exchangers. About 40 nM ethylisopropylamiloride inhibited Na(+)-H+ exchange by 50%. Ethylisopropylamiloride (10 microM) had no effect on basal or angiotensin-evoked 45Ca2+ efflux or net Ca2+ efflux. In contrast to ethylisopropylamiloride, 25-50 microM DMB, which strongly inhibits Na(+)-Ca2+ exchange, markedly decreased both 45Ca2+ efflux and net Ca2+ efflux produced by angiotensin. Replacing extracellular Na+ with N-methyl-D-glucamine inhibited angiotensin-evoked 45Ca2+ efflux similarly to DMB. Neither DMB nor Na+ placement had any effect on basal or angiotensin-evoked production of [3H]inositol phosphates. These findings suggest that Na(+)-H+ exchange has no major influence on short-term Ca2+ regulation and provide evidence that Na(+)-Ca2+ exchange is a major pathway of rapid Ca2+ efflux in stimulated arterial muscle cells.

Effect of vasopressin on Na+ kinetics in cultured rat vascular smooth muscle cells

The effect of arginine vasopressin (AVP) on Na+ kinetics was examined in cultured rat vascular smooth muscle cells (VSMC) and rat renal papillary collecting tubule cells (RPCT) by the direct measurement of intracellular sodium concentration [(Na+]i) using fluorescence dye; SBFI. AVP increased [Na+]i in a dose-dependent manner at a concentration of 10(-9) M or higher in rat VSMC but did not affect [Na+]i in rat RPCT. The calcium (Ca2+)-free solution completely blocked the increasing effect of AVP on [Na+]i in rat VSMC. A Ca2+ ionophore, ionomycin (1-2 x 10(-6) M) increased [Na+]i both in rat VSMC and RPCT. The Ca2(+)-free solution abolished the ionomycin-increased [Na+]i both in rat VSMC and RPCT. These results therefore indicate that after binding the V1 receptor AVP increases [Na+]i mediated through an increase in cellular Ca2+ uptake in VSMC.

Sodium-lithium countertransport activity in red cells of patients with insulin dependent diabetes and nephropathy and their parents

OBJECTIVE

To determine whether there are familial and genetic aspects of sodium-lithium countertransport activity in red cells in diabetic nephropathy.

DESIGN

Case-control study.

SETTING

Teaching hospital diabetic clinic.

SUBJECTS

40 Patients with insulin dependent diabetes, both of whose parents were alive: 20 with persistent proteinuria and 20 with normal albumin excretion matched for age, duration of diabetes, and body mass index. All 80 parents.

MAIN OUTCOME MEASURES

Sodium-lithium countertransport activity in red cells and arterial blood pressure.

RESULTS

Sodium-lithium countertransport activity in red cells was higher in the patients with proteinuria than in the patients with normoalbuminuria (mean (95% confidence interval) 0.47 (0.39 to 0.54) v 0.33 (0.28 to 0.38) mmol/l red cells/h respectively, p = 0.0036; mean difference 0.14 (0.04 to 0.22)). The mean countertransport activity for the two parents of each patient was calculated, and from this the mean value for each group of parents was calculated; the value was higher in the parents of the patients with proteinuria than in the parents of the patients with normoalbuminuria (0.40 (0.32 to 0.48) v 0.30 (0.26 to 0.33) mmol/l red cells/h respectively, p = 0.016; 0.10 (0.02 to 0.19)). Twenty-eight of the parents of the patients with proteinuria compared with 12 of the parents of the patients with normoalbuminuria had a countertransport activity that was above the median value in all 80 parents (p less than 0.001). Mean arterial blood pressure in the parents of the patients with proteinuria was related to that of their offspring (r = 0.46; p less than 0.01). There was a positive correlation between the sodium-lithium countertransport activity in red cells in the parents and their offspring when all parents and patients were considered (r = 0.37; p less than 0.001).

CONCLUSIONS

Increased sodium-lithium countertransport activity in red cells in the parents of diabetic patients with nephropathy provides further evidence that familial, and possibly genetic, factors related to a predisposition to arterial hypertension have a role in the susceptibility of diabetic renal disease.

Alpha 1-adrenoceptor stimulation increases intracellular pH and Ca2+ in cardiomyocytes through Na+/H+ and Na+/Ca2+ exchange

The effects of alpha 1-adrenergic stimulation on intracellular pH (pHi) and Ca2+ concentration ([Ca2+]i) were investigated in isolated rat cardiomyocytes with fluorescence dyes, BCECF and fura-2, respectively. In the presence of 5 or 25 mM HCO3- norepinephrine (NE) increased pHi in a dose-dependent manner. Intracellular alkalinization was inhibited by prazosin and phentolamine but not by yohimbine. NE-induced alkalinization was inhibited in the presence of a Na+/H+ exchange inhibitor (5-(N,N-hexamethylene) amiloride (HMA)), a C kinase inhibitor (H-7) or a calmodulin inhibitor (W-7), or in the absence of extracellular Na+. NE also increased [Ca2+]i following the pHi increase, which was abolished in the absence of extracellular Na+ or Ca2+. This Ca2+ influx was inhibited by HMA but not by diltiazem (10(-5) M). Thus, we conclude that alpha 1-adrenergic stimulation enhances Na+/H+ exchange by activation of C kinase, thereby allowing intracellular alkalinization, and that subsequent activation of Na+/Ca2+ exchange increases Ca2+ influx.

Kinetic properties of the Na+/H+ antiporter of lymphocytes from the spontaneously hypertensive rat: role of intracellular pH

Enhanced activity of the Na+/H+ antiporter is increasingly reported as a feature of cells from hypertensive subjects but the intracellular pH (ipH) dependency of its activity has not been examined. This study was designed to characterize the kinetic properties of the Na+/H+ antiporter in lymphocytes from adult spontaneously hypertensive rats (SHR) and in those from age-matched normotensive Wistar-Kyoto (WKY) controls. Steady-state ipH, estimated from the measurement of BCECF fluorescence, was significantly lower in lymphocytes from the SHR than in those from WKY rats (7.09 +/- 0.02, n = 17 and 7.17 +/- 0.03, n = 19, respectively, P less than 0.025). The velocity of the antiporter determined from the product of the change in intracellular hydrogen ion concentration (i[H+]) by the buffering power measured concurrently at each starting ipH exhibited similar kinetic parameters in SHR and WKY cells: Vmax, 72 +/- 18 vs. 79 +/- 24 mM H+/30 s; pKH, 10.04 +/- 0.87 vs. 8.49 +/- 0.80; and Hill coefficient, 1.67 +/- 0.12 vs. 1.44 +/- 0.10, respectively. Likewise, no significant differences were observed between SHR and WKY cells in either the Km (29 +/- 5 and 32 +/- 8 mM, respectively) or the Vmax (6.0 +/- 1.0 and 5.53 +/- 1.0 mM H+/30 s, respectively) of the sodium activation curve. We conclude that while the ipH of SHR lymphocytes is reduced, the kinetic properties of the Na+/H+ antiporter are virtually identical in SHR and WKY lymphocytes. Consequently, a primary abnormality in the activity of this antiporter is not an inherent feature of lymphocytes from the SHR model of genetic hypertension. We propose that the activity of the Na+/H+ antiporter in SHR cells is apt to be increased as a result of reduction in ipH which dictates a higher set point in its steady-state activity.