Contraction of vascular smooth muscle in cell culture

Tracing G-Protein-Mediated Contraction and Relaxation in Vascular Smooth Muscle Cell Spheroids

Analyses of G-protein-mediated contraction and relaxation of vascular smooth muscle cells (VSMCs) are usually hampered by a rigid growth surface and culture conditions promoting cell proliferation and a less contractile phenotype. Our studies indicated that mouse aortic VSMCs cultured in three-dimensional spheroids acquire a quiescent contractile status while decreasing the baseline G-protein-dependent inositolphosphate formation and increasing the expression of endothelin receptor type A (Ednra). Endothelin-1 (ET-1) promoted inositolphosphate formation in VSMC spheroids, but not in VSMCs cultured under standard conditions. To trace ET-1-mediated contraction of VSMC spheroids, we developed an assay by adhering them to collagen hydrogels and recording structural changes by time-lapse microscopy. Under these conditions, mouse and human VSMC spheroids contracted upon treatment with ET-1 and potassium chloride or relaxed in response to caffeine and the prostacyclin analogue Iloprost. ET-1 activated AKT-, MKK1-, and MKK3/6-dependent signaling cascades, which were inhibited by an overexpressing regulator of G-protein signaling 5 (Rgs5) to terminate the activity of Gα subunits. In summary, culture of VSMCs in three-dimensional spheroids lowers baseline G-protein activity and enables analyses of both contraction and relaxation of mouse and human VSMCs. This model serves as a simple and versatile tool for drug testing and investigating G-protein-depending signaling.

Salusin-β, a TOR2A gene product, promotes proliferation, migration, fibrosis, and calcification of smooth muscle cells and accelerates the imbalance of vasomotor function and vascular remodeling in monocrotaline-induced pulmonary hypertensive rats

Purpose: The hyper-proliferation, promoted migration, fibrosis, and calcification of pulmonary arterial smooth muscle cells (PASMCs) play critical roles in pulmonary artery (PA) continuous contraction and vascular remodeling, leading to elevated pulmonary arterial resistance and pulmonary hypertension (PH). In this study, we sought to ascertain the effects of a TOR2A gene product, salusin-β, on PASMCs’ proliferation, migration, fibrosis, calcification, and the imbalance of vasomotor function as well as pulmonary vascular remodeling in monocrotaline (MCT)-induced PH rats and their underlying mechanisms.

Methods: Knockdown or overexpression of salusin-β in rats or PASMCs was performed through tail vein injection or cell transfection of virus. The right ventricular systolic pressure (RVSP) of the rat was measured by right ventricle catheterization. Sodium nitroprusside (SNP) or acetylcholine (ACh)-induced dose-dependent relaxation was used to evaluate the vasodilatation function. Primary PASMCs were isolated from the PAs of control and PH rats.

Results: The salusin-β protein expressions were significantly increased in PAs and PASMCs isolated from PH rats compared with control rats. Knockdown of salusin-β in rats decreased high K⁺ solution-induced contraction, RVSP and RV hypertrophy index, improved SNP or ACh-induced vascular relaxation of PAs, and relieved vascular remodeling and calcification of PAs from PH rats. Silencing salusin-β in PASMCs isolated from PH rats alleviated the proliferation, migration, fibrosis, and calcification, as well as the NAD(P)H oxidase activity and reactive oxygen species (ROS) level. Overexpression of salusin-β exerted the opposite effects on vasomotor function and vascular remodeling, and PASMCs proliferation, migration, fibrosis and calcification.

Conclusion: Increased salusin-β activity in PAs from PH rats contributes to PASMCs proliferation, migration, fibrosis, and calcification, leading to the imbalance of vascular contraction and relaxation and vascular remodeling through stimulating the production of NAD(P)H oxidase derived ROS.

AMPK and Pulmonary Hypertension: Crossroads Between Vasoconstriction and Vascular Remodeling

Pulmonary hypertension (PH) is a debilitating and life-threatening disease characterized by increased blood pressure within the pulmonary arteries. Adenosine monophosphate-activated protein kinase (AMPK) is a heterotrimeric serine-threonine kinase that contributes to the regulation of metabolic and redox signaling pathways. It has key roles in the regulation of cell survival and proliferation. The role of AMPK in PH is controversial because both inhibition and activation of AMPK are preventive against PH development. Some clinical studies found that metformin, the first-line antidiabetic drug and the canonical AMPK activator, has therapeutic efficacy during treatment of early-stage PH. Other study findings suggest the use of metformin is preferentially beneficial for treatment of PH associated with heart failure with preserved ejection fraction (PH-HFpEF). In this review, we discuss the "AMPK paradox" and highlight the differential effects of AMPK on pulmonary vasoconstriction and pulmonary vascular remodeling. We also review the effects of AMPK activators and inhibitors on rescue of preexisting PH in animals and include a discussion of gender differences in the response to metformin in PH.

Regulation of SMC traction forces in human aortic thoracic aneurysms

Smooth muscle cells (SMCs) usually express a contractile phenotype in the healthy aorta. However, aortic SMCs have the ability to undergo profound changes in phenotype in response to changes in their extracellular environment, as occurs in ascending thoracic aortic aneurysms (ATAA). Accordingly, there is a pressing need to quantify the mechanobiological effects of these changes at single cell level. To address this need, we applied Traction Force Microscopy (TFM) on 759 cells coming from three primary healthy (AoPrim) human SMC lineages and three primary aneurysmal (AnevPrim) human SMC lineages, from age and gender matched donors. We measured the basal traction forces applied by each of these cells onto compliant hydrogels of different stiffness (4, 8, 12, 25 kPa). Although the range of force generation by SMCs suggested some heterogeneity, we observed that: 1. the traction forces were significantly larger on substrates of larger stiffness; 2. traction forces in AnevPrim were significantly higher than in AoPrim cells. We modelled computationally the dynamic force generation process in SMCs using the motor-clutch model and found that it accounts well for the stiffness-dependent traction forces. The existence of larger traction forces in the AnevPrim SMCs were related to the larger size of cells in these lineages. We conclude that phenotype changes occurring in ATAA, which were previously known to reduce the expression of elongated and contractile SMCs (rendering SMCs less responsive to vasoactive agents), tend also to induce stronger SMCs. Future work aims at understanding the causes of this alteration process in aortic aneurysms.

How is the human umbilical artery regulated?

The purpose of this review is to present an update of the main mechanisms involved in the physiological regulation of contraction and relaxation of the human umbilical artery (HUA) smooth muscle cells. A literature review was performed based on the analysis of papers available on PubMed. The most important and relevant studies regarding the regulation of the HUA are presented in this article. The vascular smooth muscle is a highly specialized structure, whose main function is to regulate the vascular tonus. This is controlled by a balance between the cellular signaling pathways that mediate contraction and relaxation. The cells responsible for the contractile property of this muscle are the smooth muscle cells (SMC), and an excellent source of these cells is the HUA, involved in fetoplacental circulation. Since the umbilical blood vessels are not innervated, the HUA tonus is modulated by vasoactive substances that regulate the contractile process. The main vasoactive substances that induce contraction are serotonin, histamine, thromboxane, bradykinin, endothelin 1 and prostaglandin F2α, that are linked to the activation of proteins G_q and G_i/0 . On the other hand, the main vasorelaxation mechanisms are the activation of adenyl and guanil cyclases, potassium channels and the inhibition of calcium channels. The SMC from the HUA allow the study of different cellular mechanisms and their functions. Therefore, these cells are an important tool to study the mechanisms regulating the contractility of this artery, allowing to detect potential therapeutic targets to treat HUA disorders (gestational hypertension and pre-eclampsia).

Effect of oral nitrate supplementation on pulmonary hemodynamics during exercise and time trial performance in normoxia and hypoxia: a randomized controlled trial

Background: Hypoxia-induced pulmonary vasoconstriction increases pulmonary arterial pressure (PAP) and may impede right heart function and exercise performance. This study examined the effects of oral nitrate supplementation on right heart function and performance during exercise in normoxia and hypoxia. We tested the hypothesis that nitrate supplementation would attenuate the increase in PAP at rest and during exercise in hypoxia, thereby improving exercise performance.

Methods: Twelve trained male cyclists [age: 31 ± 7 year (mean ± SD)] performed 15 km time-trial cycling (TT) and steady-state submaximal cycling (50, 100, and 150 W) in normoxia and hypoxia (11% inspired O₂) following 3-day oral supplementation with either placebo or sodium nitrate (0.1 mmol/kg/day). We measured TT time-to-completion, muscle tissue oxygenation during TT and systolic right ventricle to right atrium pressure gradient (RV-RA gradient: index of PAP) during steady state cycling.

Results: During steady state exercise, hypoxia elevated RV-RA gradient (p > 0.05), while oral nitrate supplementation did not alter RV-RA gradient (p > 0.05). During 15 km TT, hypoxia lowered muscle tissue oxygenation (p < 0.05). Nitrate supplementation further decreased muscle tissue oxygenation during 15 km TT in hypoxia (p < 0.05). Hypoxia impaired time-to-completion during TT (p < 0.05), while no improvements were observed with nitrate supplementation in normoxia or hypoxia (p > 0.05).

Conclusion: Our findings indicate that oral nitrate supplementation does not attenuate acute hypoxic pulmonary vasoconstriction nor improve performance during time trial cycling in normoxia and hypoxia.

Resveratrol induces vascular smooth muscle cell differentiation through stimulation of SirT1 and AMPK

Phenotypic plasticity in vascular smooth muscle cells (VSMC) is necessary for vessel maintenance, repair and adaptation to vascular changes associated with aging. De-differentiated VSMC contribute to pathologies including atherosclerosis and intimal hyperplasia. As resveratrol has been reported to have cardio- protective effects, we investigated its role in VSMC phenotypic modulation. We demonstrated the novel finding that resveratrol promoted VSMC differentiation as measured by contractile protein expression, contractile morphology and contraction in collagen gels. Resveratrol induced VSMC differentiation through stimulation of SirT1 and AMPK. We made the novel finding that low or high dose resveratrol had an initially different mechanism on induction of differentiation. We found that low dose resveratrol stimulated differentiation through SirT1-mediated activation of AKT, whereas high dose resveratrol stimulated differentiation through AMPK-mediated inhibition of the mTORC1 pathway, allowing activation of AKT. The health effects of resveratrol in cardiovascular diseases, cancer and longevity are an area of active research. We have demonstrated a supplemental avenue where-by resveratrol may promote health by maintaining and enhancing plasticity of the vasculature.

Hypoxic pulmonary vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

Cyclic strain induces dual-mode endothelial-mesenchymal transformation of the cardiac valve

Endothelial-mesenchymal transformation (EMT) is a critical event for the embryonic morphogenesis of cardiac valves. Inducers of EMT during valvulogenesis include VEGF, TGF-β1, and wnt/β-catenin (where wnt refers to the wingless-type mammary tumor virus integration site family of proteins), that are regulated in a spatiotemporal manner. EMT has also been observed in diseased, strain-overloaded valve leaflets, suggesting a regulatory role for mechanical strain. Although the preponderance of studies have focused on the role of soluble mitogens, we asked if the valve tissue microenvironment contributed to EMT. To recapitulate these microenvironments in a controlled, in vitro environment, we engineered 2D valve endothelium from sheep valve endothelial cells, using microcontact printing to mimic the regions of isotropy and anisotropy of the leaflet, and applied cyclic mechanical strain in an attempt to induce EMT. We measured EMT in response to both low (10%) and high strain (20%), where low-strain EMT occurred via increased TGF-β1 signaling and high strain via increased wnt/β-catenin signaling, suggesting dual strain-dependent routes to distinguish EMT in healthy versus diseased valve tissue. The effect was also directionally dependent, where cyclic strain applied orthogonal to axis of the engineered valve endothelium alignment resulted in severe disruption of cell microarchitecture and greater EMT. Once transformed, these tissues exhibited increased contractility in the presence of endothelin-1 and larger basal mechanical tone in a unique assay developed to measure the contractile tone of the engineered valve tissues. This finding is important, because it implies that the functional properties of the valve are sensitive to EMT. Our results suggest that cyclic mechanical strain regulates EMT in a strain magnitude and directionally dependent manner.

Isolation and culture of human umbilical artery smooth muscle cells expressing functional calcium channels

The human umbilical cord is a biological sample that can be easily obtained just after birth. A methodology was developed to perform cultures of human umbilical artery smooth muscle cells (HUASMC) expressing contractile proteins and functional ionic channels. To avoid fibroblast and endothelial cell contamination, we mechanically separated the tunica media, which only contains HUASMC and matrix proteins. To isolate the cells, collagenase V and elastase were used as hydrolyzing enzymes. The isolated cells were plated in collagen-coated dishes to obtain cultures of HUASMC. The cells obtained after different passages (1 to 6) exhibit the characteristic vascular smooth cell morphology and express smooth muscle alpha-2 actin, myosin heavy chain SM1, and alpha subunits of L- and T-type calcium channels (Cav 1.2, Cav 1.2, and Cav 3.2). Electrophysiology recordings for L- and T-type calcium channels were made, indicating that these channels are functional in the cultured cells. In conclusion, the procedure developed allows obtaining cultures of HUASMC expressing contractile proteins and also functional ionic channels. These cells could be used to study cellular and molecular aspects about the regulation of the vascular function.

Serotonin induces vasoconstriction of smooth muscle cell-rich neointima through 5-hydroxytryptamine2A receptor in rabbit femoral arteries

BACKGROUND

Smooth muscle cell (SMC)-rich intima is a morphological feature of atherosclerotic lesions that is observed in eroded plaque and spastic arteries. Arteries with SMC-rich intima are susceptible to vasoconstriction or vasospasm against some vasoactive agents.

OBJECTIVE

The present study evaluates the contribution of SMC-rich intima to thrombogenic vasoconstriction.

METHODS

We established SMC-rich neointima by damaging rabbit femoral arteries using balloons and then measured the isometric tension of the femoral strips against 5-hydroxytryptamine (5-HT), adenosine diphosphate, adenosine triphosphate and thrombin.

RESULTS

Among these agents, only 5-HT induced a hypercontractile response of the injured arteries with SMC-rich neointima, compared with non-injured arteries. Smooth muscle cells of both the neointima and media expressed 5-HT(2A) receptor, and sarpogrelate, a selective 5-HT(2A) receptor antagonist significantly inhibited the hypercontraction. Furthermore, 5-HT induced contraction of separated neointima and hypercontraction of separated media compared with non-injured media. Sarpogrelate and fasudil, a specific Rho-kinase inhibitor, significantly suppressed such contraction of both the neointima and media of injured arteries.

CONCLUSIONS

These results suggest that 5-HT plays a crucial role in thrombogenic vasoconstriction, and that SMC-rich intima as well as media directly contributes to the hypercontractile response of atherosclerotic vessels through the 5-HT(2A) receptor and the Rho-kinase pathway.

Matrix synthesis by bladder smooth muscle cells is modulated by stretch frequency

The bladder is a physically active organ that undergoes periodic stretching as a part of its normal function. To determine the role that stretching or mechanical deformation may play in altering the synthetic phenotype of bladder wall cells, a series of experiments were carried out to quantify several extracellular matrix (ECM) messenger ribonucleic acids (mRNAs) and their corresponding protein levels after mechanical challenge. Bladder smooth muscle cells were grown on distensible membranes in an apparatus that can reliably and reproducibly subject cells to well-characterized periods of mechanical stretching. For this study, cultured bovine bladder cells were subjected to cyclic mechanical deformation of varying frequencies to determine if this variable altered ECM expression. Using this experimental system, we demonstrated that smooth muscle cells were acutely sensitive to mechanical deformation and showed alteration in the synthesis of the major fibrillar collagens, types I and III. Concomitant analyses of mRNA in these cells show that levels of type I collagen correlate with mRNA levels at all frequencies except at 60 cycles/min, and, thus, type I production appears to be transcriptionally regulated. Interestingly, type III protein levels do not correlate with mRNA measurements except at 20 cycles/min, and, therefore, a different regulatory mechanism likely governs type III production. These studies demonstrate that smooth muscle cell ECM secretory phenotype can be altered by the frequency of mechanical deformation experienced by the cells. These data support the concept that stretching of the bladder wall affects the secretory phenotype of smooth muscle cells and can result in an altered ECM composition.

Contraction of cultured human uterine smooth muscle cells after stimulation with endothelin-1

To our knowledge, the problem of how to maintain isolated smooth cells in a "contractile" phenotypic state without deviation after subculturing has yet to be resolved. The present study characterized the in vitro contractile response of human uterine smooth muscle cell to endothelin-1, which induces contractions in isolated uterine strips. Contractile effects were qualitatively investigated using silicone rubber substrata. Endothelin-1 was able to distort and reduce the wrinkles in the silicone surface. Contractions were also quantified by measuring the resulting change in the collagen lattice area. Endothelin-1 significantly increased the contractile response in a dose-dependent manner by selectively activating endothelin A receptors. When myometrial cells were cultured within collagen lattices, a microfilament-disrupting agent, cytochalasin B, abolished contractions, and no change was observed in smooth muscle alpha-actin immunostaining. Taken together, these observations show that the uterine smooth muscle cells are contractile and respond appropriately to a potent uterotonic agent. Based on these findings, a cultured uterine smooth muscle cell model, which could be used to elucidate the mechanisms controlling uterine activity, is proposed.

Smooth muscle cells contract in response to fluid flow via a Ca2+-independent signaling mechanism

Smooth muscle cells (SMC) are exposed to fluid shear stress because of transmural (interstitial) flow across the arterial wall. This shear stress may play a role in the myogenic response and flow-mediated vasomotion. We, therefore, examined the effects of fluid flow on contraction of rat aortic SMC. SMC that had been serum-starved to induce a contractile phenotype were plated on quartz slides and exposed to controlled shear stress levels in a flow chamber. The area of the cells was quantified, and reduction in the cell area was reported as contraction. At 25 dyn/cm(2), significant area reduction was apparent 3 min after the onset of flow and exceeded 30% at 30 min. At 1 dyn/cm(2), significant contraction was not observed at 30 min. The threshold for significant shear-induced contraction appeared to be 11 dyn/cm(2). The signal transduction mechanism was studied at 25 dyn/cm(2). Intracellular calcium was imaged by using the calcium-sensitive fluorescent dye fura 2-AM. There was no detectable change in intracellular calcium during 10 min of exposure to shear stress, even though the cells displayed a significant calcium response to thapsigargin, calcium ionophore, and KCl. Further studies using pathway inhibitors provided evidence that the most important signal transduction pathway mediating calcium-independent contraction in response to fluid flow is the Rho-kinase pathway, although there was a suggestion that protein kinase C plays a secondary role.

Contractile responses and myosin phosphorylation in reconstituted fibers of smooth muscle cells from the rat cerebral artery

String-shaped reconstituted smooth muscle fibers were prepared in rectangular wells by thermal gelation of a mixed solution of collagen and cultured smooth muscle cells derived from the rat cerebral artery. The fibers contracted in response to KCl, 5-hydroxytryptamine (5-HT), noradrenaline, endothelin-1, endothelin-2, angiotensin II, prostaglandin F2alpha and prostaglandin E2. 5-HT-induced contraction was partially inhibited by the L-type voltage-dependent Ca2+ channel inhibitor nifedipine, putative non-selective cationic channel inhibitor SKF96365 and intracellular Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA-AM), and completely abolished by the myosin light chain kinase inhibitor ML-9. The fibers pre-contracted by 5-HT were completely relaxed by the Rho kinase inhibitor Y-27632, serine/threonine kinase inhibitor staurosporine, 8-bromo cyclic GMP and papaverine, and partially relaxed by dibutyryl cyclic AMP. Moreover, 5-HT as well as endothelin-1 and KCl enhanced 20-kDa myosin light chain phosphorylation in the fibers. These results suggested that the characteristics of contraction of the fibers reflect typical contractilities of vascular smooth muscle tissues. This technique will allow us to directly address questions relating to heterogeneity of receptor mechanisms and intracellular pathways of vascular smooth muscle contraction as a function of vessel type.

Remodeling of the actin cytoskeleton in the contracting A7r5 smooth muscle cell

It has been proposed that the reorganization of components of the actin cytomatrix could contribute to force development and the low energy cost of sustained contraction in contractile cells which lack a structured sarcomere (A.S. Battistella-Patterson, S. Wang and G.L. Wright (1997) Can J Physiol Pharmacol 75: 1287-1299). However, there has been no direct evidence of an apropos actin reorganization specifically linked to the contractile response in cells of this type. Remodeling of the alpha- and beta-actin domains was studied in A7r5 smooth muscle cells during phorbol 12,13 dibutyrate (PDB)-induced contraction using immunohistologic staining and beta-actin-green fluorescent protein (beta-actin-GFP) fusion protein expression. Cell stained with phalloidin as well as cells expressing beta-actin-GFP showed densely packed actin stress cables, arranged in parallel and extending across the cell body. PDB caused approximately 85% of cells to contract with evidence of forcible detachment from peripheral adhesion sites seen in many cells. The contraction of the cell body was not uniform but occurred along a principal axis parallel to the system of densely packed beta-actin cables. During the interval of contraction, the beta-actin cables shortened without evidence of disassembly or new cable formation. The use of cytochalasin to inhibit actin polymerization resulted in the dissolution of the actin cables at the central region of the cell and caused the elongation of precontracted cells. In unstimulated cells, alpha-actin formed cables similar in arrangement to the cell spanning beta-actin cables. Within a short interval after PDB addition; however, the majority of alpha-actin cables disassembled and reformed into intensely fluorescing column-like structures extending vertically from the cell base at the center of clusters of alpha-actin filaments. The alpha-actin columns of contracting cells showed strong colocalization of alpha-actinin suggesting they could be structurally analogous to the dense bodies of highly differentiated smooth muscle cells. The results indicate that the alpha- and beta-actin domains of A7r5 cells undergo a highly structured reorganization during PDB-induced contraction. The extent and nature of this restructuring suggest that remodeling could play a role in contractile function.

A human tissue-engineered vascular media: a new model for pharmacological studies of contractile responses

Our method for producing tissue-engineered blood vessels based exclusively on the use of human cells, i.e., without artificial scaffolding, has previously been described (1). In this report, a tissue-engineered vascular media (TEVM) was specifically produced for pharmacological studies from cultured human vascular smooth muscle cells (VSMC). The VSMC displayed a differentiated phenotype as demonstrated by the re-expression of VSMC-specific markers and actual tissue contraction in response to physiological stimuli. Because of their physiological shape and mechanical strength, rings of human TEVM could be mounted on force transducers in organ baths to perform standard pharmacological experiments. Concentration-response curves to vasoconstrictor agonists (histamine, bradykinin, ATP, and UTP) were established, with or without selective antagonists, allowing pharmacological characterization of receptors (H1, B2, and P2Y1, and pyrimidinoceptors). Sustained agonist-induced contractions were associated with transient increases in cytosolic Ca2+ concentration, suggesting sensitization of the contractile machinery to Ca2+. ATP caused both Ca2+ entry and Ca2+ release from a ryanodine- and caffeine-sensitive store. Increased cyclic AMP or cyclic GMP levels caused relaxation. This human TEVM displays many of functional characters of the normal vessel from which the cells were originally isolated, including contractile/relaxation responses, cyclic nucleotide sensitivity, and Ca2+ handling mechanisms comparable to those of the normal vessel from which the cells were originally isolated. These results demonstrate the potential of this human model as a versatile new tool for pharmacological research.

Agonist-induced isometric contraction of smooth muscle cell-populated collagen gel fiber

String-shaped reconstituted smooth muscle (SM) fibers were prepared in rectangular wells by thermal gelation of a mixed solution of collagen and cultured SM cells derived from guinea pig stomach. The cells in the fiber exhibited an elongated spindle shape and were aligned along the long axis. The fiber contracted in response to KCl (140 mM), norepinephrine (NE; 10(-7) M), epinephrine (10(-7) M), phenylephrine (10(-6) M), serotonin (10(-6) M), and histamine (10(-5) M), but not acetylcholine (10(-5) M). Phentolamine (10(-7) M) produced a parallel rightward shift of the NE dose-response curve. Moreover, NE-induced contraction was partially inhibited by nifedipine and completely abolished by the intracellular Ca(2+) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester, the myosin light chain kinase inhibitor ML-9, the Rho kinase inhibitor Y-27632, and papaverine. A [(3)H]quinuclidinyl benzilate binding study revealed that the loss of response to acetylcholine was due to the loss of muscarinic receptor expression during culture. The expression of contractile proteins in the fibers was similar to that in cultured SM cells. These results suggest that, although the fiber is not a model for fully differentiated SM, contractile mechanisms are maintained.

Inhibition of rat vascular smooth muscle cell proliferation by taurine and taurine analogues

The growth of rat aorta vascular smooth muscle cells (VSMCs) was measured in the presence and absence of taurine. Concentrations of taurine as low as 0.3 mM in the culture medium inhibited the proliferation of the cells, as monitored by measuring cell count, and also inhibited the rate of DNA synthesis, as examined by measuring [3H]thymidine incorporation into DNA. However, even at the highest concentration of taurine (30 mM), the doubling time of the VSMCs was only increased by 38%. Protein content of the VSMCs was decreased by 30 mM taurine. [3H]Leucine incorporation into newly synthesized protein was not affected by the highest concentration of taurine tested (30 mM), indicating that taurine did not inhibit protein synthesis but rather decreased total protein content by inhibiting cellular proliferation. The effects of other amino acids such as alanine, glycine, and serine and of various taurine analogues such as beta-alanine, guanidinoethanesulfonic acid (GES), and isethionic acid also were tested at a concentration of 20 mM for their effects on the growth of the VSMCs. Alanine, glycine, and serine had only a minimal effect or no effect on cell count, quantity of protein, and incorporation of [3H]thymidine into DNA. GES, beta-alanine, and isethionic acid had a significant effect on cell count, protein content, and incorporation of [3H]thymidine into DNA. Beta-alanine was the only analogue tested that significantly depressed [3H]leucine incorporation into newly synthesized protein. It is concluded that taurine, GES, and isethionic acid inhibited proliferation of VSMCs but did not alter normal protein synthesis or survivability of VSMCs. In contrast, other amino acids, alanine, glycine and serine, had minimal effects on VSMC proliferation and protein synthesis, whereas beta-alanine appeared to be toxic, inhibiting both VSMC synthesis and de novo protein synthesis.

Contraction of human hepatic stellate cells activated in culture: a role for voltage-operated calcium channels

BACKGROUND/AIMS

Voltage-operated calcium channels are essential for the regulation of vascular tone and are potential targets for vasodilating agents. They regulate calcium entry and thereby cell contraction in vascular cell types. Hepatic stellate cells in the activated phenotype have contractile properties and could participate in the regulation of sinusoidal blood flow. Thus, this study was aimed at investigating the presence of voltage-operated calcium channels in human hepatic stellate cells activated in culture and the effects of their stimulation on intracellular calcium concentration ([Ca2+]i) and cell contractility.

METHODS

Binding studies using [3H]-nitrendipine were performed to demonstrate the presence of voltage-operated calcium channels. Voltage-operated calcium channels were stimulated by causing cell membrane depolarization either by electrical field stimulation or extracellular high potassium. [Ca2+]i and cell contraction were measured in individual cells loaded with fura-2 using a morphometric method with an epifluorescence microscope coupled to a charge-coupled device-imaging system.

RESULTS

Binding studies demonstrated the existence of voltage-operated calcium channels in human activated hepatic stellate cells (7.1+/-1.4x10(4) sites/cell with a Kd of 2.1+/-0.1 nM). Both electrical field stimulation and potassium chloride-induced cell depolarization resulted in a marked and prolonged increase in [Ca2+]i followed by intense cell contraction. The degree of cell contraction correlated with the intensity of calcium peaks. Removal of extracellular calcium or preincubation of cells with nitrendipine, a specific antagonist of voltage-operated calcium channels, completely blocked the effects on [Ca2+]i and cell contraction, whereas preincubation of cells with BayK-8644, a specific agonist of voltage-operated calcium channels, increased calcium peaks and contraction.

CONCLUSION

Activated human hepatic stellate cells have a large number of voltage-operated calcium channels, the activation of which is associated with an increase in [Ca2+]i followed by marked cell contraction. Voltage-operated calcium channels probably play an important role in the regulation of activated hepatic stellate cells contractility.

Progesterone inhibits arterial smooth muscle cell proliferation

Mortality from atherosclerotic cardiovascular disease is lower in premenopausal women than in age-matched men. It is also lower in postmenopausal women who take estrogens and progestins together rather than estrogens alone. Progesterone receptors were detected in human and rat aortic smooth muscle cells in vivo and in vitro (in subculture). We examined the effect of progesterone on proliferation of smooth muscle cells, important constituents of atherosclerotic plaques. Progesterone at physiologic levels inhibited DNA synthesis and proliferation in these cells in a dose-dependent manner, and pretreatment with the progesterone receptor antagonist RU486 blocked inhibition. Cyclin A and E messenger RNA levels decreased after progesterone treatment but those of cyclin B and D1 did not change. This cell cycle-dependent inhibition of arterial smooth muscle cell proliferation by progesterone may represent a mechanism for the hormone's protective effect against atherosclerosis.

Acute effects of thyroid hormone on vascular smooth muscle

The enhanced cardiovascular hemodynamics associated with triiodo-L-thyronine (T3) treatment is in part mediated by a decrease in systemic vascular resistance. To determine the molecular mechanisms for the vasoactive properties of T3, we studied primary cultures of aortic endothelial and vascular smooth muscle (VSM) cells. Active tension development by the VSM cells was measured by deformation lines within a siloxane matrix on which the cells were grown. Exposure to T3 (10(-10) M) resulted in cellular relaxation within 10 min. Hormone binding studies to purified VSM cell plasma membranes identified two binding sites specific for T3 with Kd of 1 x 10(-11) and 6.1 x 10(-8) M. L-Thyroxine and reverse T3 did not compete for the L-T3 binding sites. To determine an intracellular signaling pathway of T3 action, cAMP and cGMP content were measured in VSM cell cultures treated with T3. No quantitative changes were observed in a time frame known to cause VSM cell relaxation. The level of myosin light chain phosphorylation is a major determinant of smooth muscle contraction. Thus, treatment of VSM cells with isoproterenol, a vasodilator, caused a significant decrease in radiolabeled phosphate incorporation into the myosin light chains, whereas T3 had no effect on phosphorylation of these proteins. Primary cultures of vascular endothelial cells exposed to T3 showed no nitric oxide production as measured by cellular cGMP content and nitrite release, suggesting that T3 acted directly on the VSM cell to cause vascular relaxation.

Purine and pyrimidine nucleotide metabolism of vascular smooth muscle cells in culture

1. Cultures of vascular smooth muscle cells accumulate extracellular breakdown products of purine and pyrimidine nucleotides that, over 9 hr, represent 60 +/- 7 and 78 +/- 17%, respectively, of the intracellular nucleotide content. 2. The accumulation is stimulated during contracture with 20 mM KCl or 70 microM carbachol, consistent with the notion that both pyrimidine and purine nucleotides are involved in the energetics of smooth muscle contracture. 3. Because the intracellular levels of pyrimidine and purine nucleotides remain constant, it appears likely that rates of synthesis match the rates of release. 4. Ectonucleotidases are present that can degrade ATP, UTP, and CTP. High-energy nucleotides may be the primary products released.

Human foetal lung (IMR-90) cells: myofibroblasts with smooth muscle-like contractile properties

Single cells displaying many characteristics in common with smooth muscle are now being identified in many organs. Although their origin remains elusive, they are nonetheless known to play a major role in fibroproliferative diseases and stromal reactions by virtue of their contractile properties. We have investigated the contractile properties and expression of smooth muscle-associated proteins in such a cell line derived from human foetal lung (IMR-90). For almost two decades, these cells have served as model fibroblasts in a wide variety of studies. And yet, IMR-90 cells manifest many features characteristic of differentiated smooth muscle cells: they exhibit the same elongated, slender form and the strikingly regular, longitudinal alignment of their actin-attachment sites, which are indispensable for coordinated contraction. Moreover, these adhaerens junctions also contain metavinculin, the smooth muscle analogue of vinculin, the stable expression of which has not previously been demonstrated in cultured cells. Since sm 22, as well as the smooth muscle-associated alpha-actin isoform and calponin are also expressed, IMR-90 cells must now be classified as myofibroblasts. When cultivated on a rubbery silicon surface, IMR-90 cells respond to stimulation with a rate of contraction which is considerably faster than that exhibited by fibroblasts derived from other established lines. Taken together, the regular longitudinal orientation of the adhaerens junctions, the stable expression of metavinculin, and the rapid speed of shortening in IMR-90 cells suggest, by implication, that the periodicity of actin attachment sites is a fundamental determinant of contractile efficiency in smooth muscle cells; this spacing may be mediated by metavinculin.

Actin isoform and alpha 1B-adrenoceptor gene expression in aortic and coronary smooth muscle is influenced by cyclical stretch

The occurrence of vascular domains with specific biological and pharmacological characteristics suggests that smooth muscle cells in different arteries may respond differentially to a wide range of environmental stimuli. To determine if some of these vessel-specific differences may be attributable to mechano-sensitive gene regulation, the influence of cyclical stretch on the expression of actin isoform and alpha 1B-adrenoceptor genes was examined in aortic and coronary smooth muscle cells. Cells were seeded on an elastin substrate and subjected to maximal stretching (24% elongation) and relaxation cycles at a frequency of 120 cycles/min in a Flexercell strain unit for 72 h. Total RNA was extracted and hybridized to radiolabeled cDNA probes to assess gene expression. Stretch caused a greater reduction of actin isoform mRNA levels in aortic smooth muscle cells as compared to cells from the coronary artery. Steady-state mRNA levels of alpha 1B-adrenoceptor were also decreased by cyclical stretch in both cell types but the magnitude of the response was greater in coronary smooth muscle cells. No changes in alpha 1B-adrenoceptor or beta/gamma-actin steady-state mRNA levels were observed in H4IIE cells, a nonvascular, immortalized cell line. The relative gene expression of heat shock protein 70 was not influenced by the cyclic stretch regimen in any of these cell types. These results suggest that stretch may participate in the regulation of gene expression in vascular smooth muscle cells and that this response exhibits some degree of cell-specificity.

Strain measurements in cultured vascular smooth muscle cells subjected to mechanical deformation

Early work in the field of biomechanics employed rigorous application of the principles of mechanics to the study of the macroscopic structural response of tissues to applied loads. Interest in the functional response of tissues to mechanical stimulation has lead researchers to study the biochemical responses of cells to mechanical loading. Characterization of the experimental system (i.e., specimen geometry and boundary conditions) is no less important on the microscopic scale of the cell than it is for macroscopic tissue testing. We outline a method for appropriate characterization of cell deformation in a cell culture model; describe a system for applying a uniform, isotropic strain field to cells in culture; and demonstrate a dependence of cell deformation on morphology and distribution of adhesion sites. Cultured vascular smooth-muscle cells were mechanically deformed by applying an isotropic strain to the compliant substrate to which they were adhered. The state of strain in the cells was determined by measurement of the displacements of fluorescent microspheres attached to the cell surface. The magnitude and orientation of principal strains were found to vary spatially and temporally and to depend on cell morphology. These results show that cell strain can be highly variable and emphasize the need to characterize both the loading conditions and the actual cellular deformation in this type of experimental model.

Acute effects of triiodothyronine on arterial smooth muscle cells

Thyroid hormone has profound effects on the heart and cardiovascular system. Systemic vascular resistance is uniformly decreased in both naturally occurring and experimental hyperthyroidism, and it is increased in thyroid hormone deficiency. Because vascular smooth muscle cell contraction is a major determinant of systemic vascular resistance, the present studies were designed to address the acute effects of the thyroid hormones, specifically triiodothyronine, on vascular smooth muscle cell contractile activity. Our data indicate that triiodothyronine causes smooth muscle relaxation; this property may account for some of its marked effects on the cardiovascular system. As a novel vasodilatory agent, the potential therapeutic implications for triiodothyronine may be numerous.

Development and characterization of a cloned rat pulmonary arterial smooth muscle cell line that maintains differentiated properties through multiple subcultures

BACKGROUND

Pulmonary hypertension is associated with abnormal pulmonary arterial contractility and growth. The mechanisms for these abnormalities are largely unknown. To study these processes, we sought to develop an in vitro system. Even though cultured aortic and pulmonary artery smooth muscle cells (SMCs) have been of considerable value in studying smooth muscle biology, one drawback of this system has been that these cells often lose differentiated properties in an unpredictable manner when they are passaged in culture. In addition, there appear to be significant differences in physiological and pathological responses between the systemic and pulmonary circulations, many of which could be directly related to the smooth muscle. We therefore established a cloned population of rat pulmonary arterial SMCs (PASMCs) that maintain differentiated properties through multiple subcultures.

METHODS AND RESULTS

PASMCs were obtained initially by enzymatic dissociation from pulmonary arteries of adult Sprague-Dawley rats. From these cells, clones were isolated. The cloned cells retained expression of functional surface receptors for angiotensin II, norepinephrine, and alpha-thrombin and high levels of the smooth muscle isoforms of alpha-actin, myosin heavy chain, myosin regulatory light chain, and alpha-tropomyosin mRNAs even after multiple passages. The cells could also be transfected and processed exogenous transcripts in a smooth muscle-specific fashion.

CONCLUSIONS

These cloned PASMCs retain many differentiated characteristics and should be valuable for future studies of pulmonary vascular smooth muscle cell biology.

Eicosanoid-mediated contractility of hepatic stellate cells

To approach experimentally the problem of contractility, stellate cells from rats were isolated and grown on a flexible silicone rubber substrate. Increases or decreases in the number of wrinkles of the silicone membrane beneath the cells that were easily observable by microscopy was employed as semi-quantitative measure of stellate cell motility. Contraction of stellate cells accompanied by diminution of cell body size was induced by U46619 (a thromboxane A2 analogue) and prostaglandin (PG) F2 alpha. Wrinkle formation became detectable 1.5 min after addition of 2 microM-U46619 and reached its maximum 10-15 min later. The effect of PGF2 alpha was not so striking, but lasted for a longer period of time. On the other hand, dibutyryl cyclic AMP, Iloprost (a PGI2 analogue) and PGE2 led to the disappearance or decrease in the number of wrinkles, indicating relaxation of contracted stellate cells. For instance, after addition of 2 microM-Iloprost, 47, 75 and 82% of contracted stellate cells had relaxed within 5, 10 and 20 min respectively. Moreover, dibutyryl cyclic AMP induced disappearance of alpha-smooth muscle actin stress fibres. This response became recognizable 10 min after addition of dibutyryl cyclic AMP; 40 min later, 97% of stellate cells were devoid of stress fibres. Thus stellate cells are able to undergo reversible contraction in primary culture, and the contraction of these cells may be mediated by eicosanoids that can be produced within the liver.

Acute endothelial cell contraction in vitro: a comparison with vascular smooth muscle cells and fibroblasts

The contractile responses of cultured rat and calf endothelial cells (EC), vascular smooth muscle cells (VSMC), and fibroblasts (FB) to vasoactive mediators (thrombin, serotonin, bradykinin, and histamine), forskolin, and cytochalasin B were compared. Cells were grown on a pliable silicone membrane, and contraction was assessed, using time-lapse video microscopy, by recording changes in the wrinkling of the silicone as the cells exerted tension on the surface. We found that all cells contracted in the presence of serum or thrombin and that VSMC and FB also contracted with serotonin stimulation. Bradykinin and histamine were not contractants in this system. Discrepancies between these results and reports of changes in permeability of endothelial layers in vitro and in vivo may be due to (1) the vascular segment from which EC were studied or (2) the possibility that certain mediators may provoke a noncontractile response that results in gap formation. Thus changes in vascular permeability, which occur during inflammation, may have both contractile and noncontractile components. Forskolin, known to indirectly inhibit myosin light-chain kinase activity, and cytochalasin B were potent relaxants, suggesting a similar smooth muscle-like contractile mechanism for all three cell types.

Calcium channels and nifedipine inhibition of serotonin-induced [3H]thymidine incorporation in cultured cerebral smooth muscle cells

Cultures of smooth muscle cells were prepared from the basilar artery of adult guinea pigs. Passaged cultures (10-30 passages) that expressed serotonin receptors were studied using [3H]thymidine incorporation. When tested in quiescent medium, serotonin potently stimulated [3H]thymidine incorporation (EC50 of 31 nM) by as much as 400% at 24 h. The number of cells was not significantly increased at 24 or 48 h. At concentrations of 10(-8)-10(-5) M 5-HT, [3H]thymidine uptake was reduced 40-50% by the dihydropyridine Ca2+ channel blocker, nifedipine (1 microM). To demonstrate a possible mechanism for the sensitivity to nifedipine, Ca2+ currents were measured using the whole cell patch clamp technique. The cells expressed dihydropyridine-sensitive L-type Ca2+ channels, but not other subtypes of Ca2+ channels, as indicated by the kinetic and voltage-dependent characteristics of the current and by the stimulatory effect of Bay K 8644. The magnitude of the Ca2+ currents was related exponentially to the membrane surface area, measured as cell capacitance. These data support the association of dihydropyridine-sensitive Ca2+ channels with mitogenesis in vascular smooth muscle, and suggest an alternate mechanism of action for the beneficial effect of dihydropyridines in prophylaxis of cerebral vasospasm.

Characterization of myosin heavy and light chains in cultured mesangial cells

Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated that postconfluent mesangial cells in primary culture expressed three myosin heavy chains (MHCs), 204 kD, 200 kD and 196 kD, in a manner similar to that of smooth muscle cells. The MHCs of 204 kD and 200 kD in mesangial cells reacted positively with antibodies raised against bovine aorta smooth muscle myosin while the 196 kD MHC reacted positively with antibodies against platelet myosin. Moreover, the combined content of the MHCs in cultured mesangial cells was remarkably similar in amount to that in cultured aortic smooth muscle cells. After three passages, cultured mesangial cells expressed only the 196 kD MHC as has been reported for cultured smooth muscle cells. Two phosphorylated proteins were found in the immunoprecipitate after incubation of the cell extract with antibodies against platelet myosin: a MHC of approximately 200 kD and myosin light chain (MLC) of 20 kD. The level of MLC phosphorylation was quantitated by scanning densitometry of autoradiograms. Arginine vasopressin (AVP) at 100 nM induced MLC phosphorylation with a maximum effect at 10 minutes. AVP enhanced MLC phosphorylation in a dose dependent manner: maximum response was observed with 100 nM and half maximum, at 3.5 nM. Similarly, angiotensin II (100 nM), endothelin-1 (10 nM) and the calcium ionophore, A23187 (1 microM), significantly enhanced MLC phosphorylation. Thus, although the expression of MHC was altered in quality after mesangial cells were placed in culture, the cells remained rich in myosin content and had an intact regulatory system for contraction which responded to a variety of vasoconstrictive agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Rabbit aortic smooth muscle cell culture. A model for the pharmacological study of diabetes-induced alterations in cell proliferation

Atherosclerotic vascular disease is the most common complication of diabetes mellitus. Enhanced vascular smooth muscle cell proliferation plays a central role in atherosclerotic lesion formation. Studies using explant cultures have demonstrated that aortic smooth muscle cells from rats with experimental or genetic diabetes have enhanced rates of proliferation when compared to controls. However, this method of culture may select for cells with enhanced migratory potential. In the present studies, aortic smooth muscle cells were successfully cultured from control and diabetic rabbits after enzymatic and mechanical dispersion from thoracic aortic segments. The proliferative patterns of control cells were characterized and growth rates of diabetic cells were compared to controls. Primary cultures from control rabbits grew after an initial 5-day lag period to achieve threefold increases in cell number by 9 days. Subcultures of aortic smooth muscle cells entered the logarithmic phase of growth after 2 days, reaching the plateau phase of growth in 5-7 days and achieving three to fourfold increases in cell number. The final density to which cultures grew was not affected by the number of cells attached on day 1 for the range studied. Cells from diabetic rabbits displayed shorter doubling times and reached greater densities at confluence than did cells from controls. These data support the hypothesis that diabetes induces an atherogenic response. The dissociated rabbit aortic smooth muscle cell culture provides a model in which to study diabetes-induced modulation of cell proliferation that is amenable to pharmacological manipulation to investigate agonist and growth factor-induced responses.

A large accumulation of non-muscle myosin occurs at first entry into M phase in rat vascular smooth-muscle cells

Vascular smooth-muscle cells (VSMCs) from rat aortae contained very little non-muscle myosin heavy chain (MHC) immediately after dispersal, and the protein did not accumulate if the cells were held in G0/G1 phase by withholding serum or were held in first S phase by the addition of bromodeoxyuridine (BrdU). However, non-muscle MHC accumulated by greater than 20-fold per cell during first M phase, when over 80% of the cells divided between 48 h and 72 h after addition of serum. Delaying the addition of serum caused a delay in the accumulation of the non-muscle MHC until the cells subsequently entered M phase. If the cells were held in M phase at the metaphase/anaphase boundary by nocadazole, the accumulation of non-muscle myosin still occurred, although division was blocked. When the cells were pulse-labelled with [35S]methionine, it was found that non-muscle MHC was one of the major proteins being made and that its synthesis occurred at similar rates throughout the cell cycle. This implied that the rate of degradation of the protein before first M phase was much faster than in M phase, when the protein accumulated rapidly. This was confirmed by direct measurements of the rate at which [35S]methionine-labelled non-muscle MHC disappeared from the cells, which gave a half-life for the protein of about 8 h before M phase but about 5 days in post-mitotic cells, i.e. an increase of approx. 15-fold. These data are consistent with the hypothesis that there is a mechanism in VSMCs which shortens the half-life of the protein before first M phase and that the accumulation of non-muscle MHC which results from the increase in half-life at first M phase may be necessary for division of these cells.

Hypoxic contraction of cultured pulmonary vascular smooth muscle cells

The cellular events involved in generating the hypoxic pulmonary vasoconstriction response are not clearly understood, in part because of the multitude of factors that alter pulmonary vascular tone. The goal of the present studies was to determine if a cell culture preparation containing vascular smooth muscle (VSM) cells could be made to contract when exposed to a hypoxic atmosphere. Cultures containing only fetal bovine pulmonary artery VSM cells were assessed for contractile responses to hypoxic stimuli by two methods. In the first, tension forces generated by cells grown on a flexible growth surface (polymerized polydimethyl siloxane) were manifested as wrinkles and distortions of the surface under the cells. Wrinkling of the surface was noted to progressively increase with time as the culture medium bathing the cells was made hypoxic (PO2 approximately 25 mmHg). The changes were sometimes reversible upon return to normoxic conditions and appeared to be enhanced in cells already exhibiting evidence of some baseline tone. Repeated passage in culture did not diminish the hypoxic response. Evidence for contractile responses to hypoxia was also obtained from measurements of myosin light chain (MLC) phosphorylation. Conversion of MLC to the phosphorylated species is an early step in the activation of smooth muscle contraction. Lowering the PO2 in the culture medium to 59 mmHg caused a 45% increase in the proportion of MLC in the phosphorylated form as determined by two-dimensional gel electrophoresis. Similarly, cultures preincubated for 4 h with 32P and then exposed to normoxia or hypoxia for a 5-min experimental period showed more than twice as much of the label in MLCs of the hypoxic cells.(ABSTRACT TRUNCATED AT 250 WORDS)