Functional diagnosis as a tool in rehabilitation: a comparison of teachers and other employees

Contractile cells in the mammalian lung develop in close association with the outgrowing stem bronchi. Fully differentiated smooth muscle cells are typically found in proximal regions, residing in the substantial muscular walls of the major airways and blood vessels. More distally, cells expressing markers of differentiated smooth muscle cells to a variable degree, and which may therefore possess contractile properties, are to be found scattered around the interstitium. We have investigated the temporal and spatial distribution of smooth muscle lineage markers (smooth muscle myosin mRNA) and of those indicative of contractile function (metavinculin mRNA) in the murine lung. In the smooth muscle layers of the bronchi and major blood vessels, these genes are expressed from the onset of pulmonary budding, concurrently with the appearance of alpha-smooth muscle actin and calponin proteins. During fetal development, smooth muscle-associated genes and proteins are restricted to this committed smooth muscle population. The first signs of myofibroblast or pericyte differentiation become manifest perinatally, when their expression of alpha-smooth muscle actin escalates. In the adult lung, such cells may be readily pin-pointed by their positive reaction for metavinculin mRNA, but, at maturity, they do not always coexpress alpha-smooth muscle actin.     

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Abnormal mechanical stress on pulmonary structures is associated with increased airway resistance and impaired gas exchange as a result of increased airway smooth muscle (ASM) deposition. Using an in vitro system with cultured ASM cells, we have demonstrated that cyclic deformational strain increases ASM cellular myosin and myosin light chain kinase. To determine if these contractile protein increases were accompanied by ultrastructural changes in cells indicating phenotypic modulation, cells subjected to strain were compared to cells grown under static conditions by transmission electron microscopy (TEM) and fluorescent staining. The strained ASM cells oriented perpendicular to the strain direction were more elongated and contained more actin stress fibers than identical cells grown under physically static conditions. The stress fiber bundles were thicker and reorganized parallel to the long axis of the cell. Marked increases in the numbers and lengths of focal adhesions between the cell membrane and the substratum were found by both TEM and immunostaining for talin. Mechanical strain thus increases organization of cytoskeletal elements in cultured ASM cells. Similar effects in vivo may serve to promote the expression of the contractile phenotype of cultured ASM cells independent of other in vivo factors and alter cell contractility. Increased organization of cytoskeletal elements might also increase the efficiency of signal transduction from the extracellular matrix into the cell interior.     

Caldesmon

Caldesmon is a protein that is found in smooth muscle and in non-muscle cells. Two isoform classes produced by alternative splicing of one gene have been characterized. The smooth muscle, high molecular weight (89-93 kDa), caldesmon isoforms are exclusively found in adult and fully differentiated smooth muscle cells. The non-muscle, low molecular weight (59-63 kDa), caldesmon isoforms are found in non-muscle and in de-differentiated smooth muscle cells. The conserved regions of all isoforms contain caldesmon's properties such as binding to actin, tropomyosin, Ca(2+)-calmodulin, myosin and phospholipids. All isoforms are also very potent inhibitors of the actin-tropomyosin activated myosin MgATPase. Non-muscle and smooth muscle isoforms of caldesmon perform different roles in vivo. This may be reflected by the distinct cellular distribution of these isoform classes. Non-muscle caldesmon is a regulatory factor in the microfilament network and is thus involved in the assembly and stabilization of microfilaments. Smooth muscle caldesmon together with tropomyosin is a mediating factor for Ca(2+)-dependent inhibition of smooth muscle contraction.     

Immunoelectron microscopic localization of plasminogen activator inhibitor type 1 (PAI-1) in smooth muscle cells from morphologically normal and atherosclerotic human arteries

Vascular wall fibrinolytic system proteins are believed to play a pivotal role in atherogenesis. Tissue-type plasminogen activator (t-PA) and urokinase plasminogen activator (u-PA) influence persistence of luminal thrombi and proteolysis of extracellular matrix, respectively. The major physiologic inhibitor of t-PA and u-PA is plasminogen activator inhibitor type 1 (PAI-1). All three of these fibrinolytic system proteins have been detected in vascular endothelial cells, smooth muscle cells, and macrophages by light microscopic immunohistochemistry. This study was undertaken to delineate, by immunoelectron microscopy, the loci of PAI-1 in smooth muscle cells from intact morphologically normal and atherosclerotic human arteries as well as in isolated and cultured smooth muscle cells from arteries. In intact vessels, PAI-1 immunoreactivity was associated with contractile filaments in cells in both normal and atherosclerotic tissues. Lipid-laden smooth muscle cells in atherosclerotic vessels were mainly of the synthetic phenotype and displayed lesser amounts of PAI-1 associated with rough endoplasmic reticulum and contractile filaments. Isolated smooth muscle cells exhibited either a contractile or synthetic phenotype. In the cells with a contractile phenotype, PAI-1 was associated with the contractile elements, whereas in the cells with a synthetic phenotype, the PAI-1 was associated predominantly with elements of the endoplasmic reticulum. Because PAI-1 is associated predominantly with contractile filaments in smooth muscle cells, the net amount of immunodetectable PAI-1 appears to be greater in contractile compared with synthetic phenotype cells.     

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Smooth muscle contraction is regulated primarily by the reversible phosphorylation of myosin triggered by an increase in sarcoplasmic free Ca2+ concentration ([Ca2+]i). Contraction can, however, be modulated by other signal transduction pathways, one of which involves the thin filament-associated protein calponin. The h1 (basic) isoform of calponin binds to actin with high affinity and is expressed specifically in smooth muscle at a molar ratio to actin of 1:7. Calponin inhibits (i) the actin-activated MgATPase activity of smooth muscle myosin (the cross-bridge cycling rate) via its interaction with actin, (ii) the movement of actin filaments over immobilized myosin in the in vitro motility assay, and (iii) force development or shortening velocity in permeabilized smooth muscle strips and single cells. These inhibitory effects of calponin can be alleviated by protein kinase C (PKC)-catalysed phosphorylation and restored following dephosphorylation by a type 2A phosphatase. Three physiological roles of calponin can be considered based on its in vitro functional properties: (i) maintenance of relaxation at resting [Ca2+]i, (ii) energy conservation during prolonged contractions, and (iii) Ca(2+)-independent contraction mediated by phosphorylation of calponin by PKC epsilon, a Ca(2+)-independent isoenzyme of PKC.     

Interaction between calponin and smooth muscle myosin

Calponin is a thin filament-associated protein in smooth muscle that has been shown to bind actin, tropomyosin and calmodulin, and has been implicated to play a role in regulation of smooth muscle contractility. Using a centrifugation assay we found that calponin interacts with unphosphorylated filamentous smooth muscle myosin. We found that this calponin-myosin interaction is reversed by Ca(2+)-CaM, and depends on ionic strength. At 50 mM NaCl the binding constant and the stoichiometry of this interaction were estimated to be 2 x 10(6) M-1, and 1.2-2.4 calponin per myosin, respectively. We suggest that the calponin-myosin interaction could be involved in regulation of smooth muscle contractility by anchoring myosin to actin.     

Smooth and skeletal muscle myosin both exhibit low duty cycles at zero load in vitro

Smooth muscle's stress equals that of skeletal muscle with less myosin. Thus, under isometric conditions, smooth muscle myosin may spend a greater fraction of its cycle time attached to actin in a high force state (i.e. higher duty cycle). If so, then smooth muscle myosin may also have a higher duty cycle under unloaded conditions. To test this, we used an in vitro motility assay in which fluorescently labeled actin filaments move freely over a sparsely coated (5-100 micrograms/ml) myosin surface. Actin filament velocity (V) was a function of the number of cross-bridges capable of interacting with an actin filament (N) and the duty cycle (f), V = (a x Vmax) x (1-(1-f)N) (Uyeda et al., 1990; Harada et al., 1990). N was estimated from the myosin density on the motility surface and the actin filament length. Data for V versus N were fit to the above equation to predict f. The duty cycle of smooth muscle myosin (4.0 +/- 0.7%) was not significantly different from that of skeletal muscle myosin (3.8 +/- 0.5%) in agreement with values estimated by Uyeda et al. (1990) for skeletal muscle myosin under unloaded conditions. The duty cycles of smooth and skeletal muscle myosin may still differ under isometric conditions.     

Expression of myosin heavy chain and of myogenic regulatory factor genes in fast or slow rabbit muscle satellite cell cultures

We investigated the myogenic properties of rabbit fast or slow muscle satellite cells during their differentiation in culture, with a particular attention to the expression of myosin heavy chain and myogenic regulatory factor genes. Satellite cells were isolated from Semimembranosus proprius (slow-twitch muscle; 100% type I fibres) and Semimembranosus accessorius (fast-twitch muscle; almost 100% type II fibres) muscles of 3-month-old rabbits. Satellite cells in culture possess different behaviours according to their origin. Cells isolated from slow muscle proliferate faster, fuse earlier into more numerous myotubes and mature more rapidly into striated contractile fibres than do cells isolated from fast muscle. This pattern of proliferation and differentiation is also seen in the expression of myogenic regulatory factor genes. Myf5 is detected in both fast or slow 6-day-old cell cultures, when satellite cells are in the exponential stage of proliferation. MyoD and myogenin are subsequently detected in slow satellite cell cultures, but their expression in fast cell cultures is delayed by 2 and 4 days respectively. MRF4 is detected in both types of cultures when they contain striated and contractile myofibres. Muscle-specific myosin heavy chains are expressed earlier in slow satellite cell cultures. No adult myosin heavy chain isoforms are detected in fast cell cultures for 13 days, whereas cultures from slow cells express neonatal, adult slow and adult fast myosin heavy chain isoforms at that time. In both fast and slow satellite cell cultures containing striated contractile fibres, neonatal and adult myosin heavy chain isoforms are coexpressed. However, cultures made from satellite cells derived from slow muscles express the slow myosin heavy chain isoform, in addition to the neonatal and the fast isoforms. These results are further supported by the expression of the mRNA encoding the adult myosin heavy chain isoforms. These data provide further evidence for the existence of satellite cell diversity between two rabbit muscles of different fibre-type composition, and also suggest the existence of differently preprogrammed satellite cells.     

Explaining load dependence of ventricular contractile properties with a model of excitation-contraction coupling

A theory is present which accounts for a very broad range of ventricular properties that have been noted in recent experiments. The theory is based upon a four-state biochemical scheme that accounts for the dynamic interaction between calcium, actin and myosin which includes a calcium-free force generating complex between actin and myosin. This original scheme was supplemented by incorporating two additional basic properties of cardiac muscle: length dependence of calcium binding affinity and load dependence of force generation. The biochemical scheme was used to provide the force-length-time properties of cardiac muscle which were used to construct a ventricle via a spherical geometry. In addition to being able to accurately interrelate previously measured calcium and muscle force transients, this theory was able to account for many fundamental aspects of ventricular performance including: a realistic contractility dependent curvilinearity of the end-systolic pressure-volume relationship: enhancement of contractile strength on ejecting compared to isovolumic beats; improved contractile efficiency on ejecting as compared to isovolumic beats; appropriate load-dependent changes in time to peak pressure, time constant of relaxation and duration of contraction on isovolumic and ejecting beats; realistic estimated time course of tension-dependent heat generation. The explanation for these phenomena were explored within the context of the theory and presented in detail.     

Assembly mechanism of Dictyostelium myosin II: regulation by K+, Mg2+, and actin filaments

Regulated assembly of myosin II in Dictyostelium discoideum amoebae partially controls the orderly formation of contractile structures during cytokinesis and cell migration. Kinetic and structural analyses show that Dictyostelium myosin II assembles by a sequential process of slow nucleation and controlled growth that differs in rate and mechanism from other conventional myosins. Nuclei form by an ordered progression from myosin monomers to parallel dimers to 0.43 microns long antiparallel tetramers. Lateral addition of dimers to bipolar tetramers completes the assembly of short (0.45 microns) blunt-ended thick filaments. Myosin heads are not staggered along the length of tapered thick filaments as in skeletal muscle, nor are bipolar minifilaments formed as in Acanthamoeba. The overall assembly reaction incorporating both nucleation and growth could be kinetically characterized by a second-order rate constant (kobs,N+G) of 1.85 x 10(4) M-1 s-1. Individual rate constants obtained for nucleation, kobs,N = 4.5 x 10(3) M-1 s-1, and growth, kobs,G = 2.5 x 10(4) M-1 s-1, showed Dictyostelium myosin II to be the slowest assembling myosin analyzed to date. Nucleation and growth stages were independently regulated by Mg2+, K+, and actin filaments. Increasing concentrations of K+ from 50 to 150 mM specifically inhibited lateral growth of dimers off nuclei. Intracellular concentrations of Mg2+ (1 mM) accelerated nucleation but maintained distinct nucleation and growth phase kinetics. Networks of actin filaments also accelerated the nucleation stage of assembly, mechanistically accounting for spontaneous formation of actomyosin contractile fibers via myosin assembly (Mahajan et al., 1989). The distinct assembly mechanism and regulation utilized by Dictyostelium myosin II demonstrates that myosins from smooth muscle, striated muscle, and two types of amoebae form unique thick filaments by different pathways.     

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Diabetes mellitus is a major risk factor for atherosclerosis. In atherosclerotic lesions, arterial smooth muscle cells (SMC) change from a contractile to a synthetic phenotype characterized by active proliferation. A similar phenotype modulation occurs in vitro when isolated arterial SMC are grown in culture and is characterized by both changes in cell morphology and a typical switch in actin isoform expression. In this study, we examined the influence of streptozotocin (STZ)-induced diabetes on the differentiation state and the phenotype modulation of cultured rat aortic SMC. We used transmission electron microscopy to study the fine structure of STZ-diabetic and non-diabetic SMC in primary culture and immunological methods for the determination of the proportions of alpha-smooth muscle actin (alpha-SM) and nonmuscle beta-actin (beta-NM) isoforms. Cultured STZ-diabetic SMC exhibited a large cytoplasmic volume, rich in rough endoplasmic reticulum, when compared with cultured non-diabetic SMC. alpha-SM, organized in stress fibers, was less homogeneously and abundantly distributed and by contrast, beta-NM was more abundant in STZ-diabetic than in non-diabetic SMC. Cytofluorimetric analyses demonstrated that the alpha-SM content was reduced in freshly STZ-diabetic SMC. Furthermore, during logarithmic growth of cultured SMC, the decrease of alpha-SM was more important in STZ-diabetic than in non-diabetic SMC. Immunoblotting of actin isoforms confirmed that expression of beta-NM was more important in STZ-diabetic than in non-diabetic SMC even in freshly isolated cells. The results suggest that SMC from STZ-diabetic rats express a more dedifferentiated state and undergo a more rapid phenotypic modulation in primary cultures than SMC from non-diabetic rats. Therefore, diabetes could induce changes in the phenotype of arterial SMC which might be associated with the onset or progression of the atherogenic process.     

Ultrastructural and immunohistochemical studies of Wharton's jelly umbilical cord cells

In order to determine the significance of Wharton's jelly, the characteristics of these cells were examined by means of electron microscopy and immunohistochemistry. These cells possessed ultrastructural characteristics of both fibroblasts and smooth muscle cells, indicating that they are modified, rather than typical fibroblasts. Immunohistochemically those 'myofibroblasts' stained positive for actin, non-muscle myosin, vimentin and desmin. Staining for muscle myosin was negative, supporting the ultrastructural findings. As our results indicate that these cells can function in both fibrogenesis and cell contraction, we speculate that they may contribute to the elasticity of Wharton's jelly, by synthesizing collagen fibers, and participate in the regulation of umbilical blood flow by virtue of their contractile properties.     

Primary structure of bovine Hageman factor (blood coagulation factor XII): comparison with human and guinea pig molecules

An understanding of the consequences of autologous vein grafting reveals both the reasons why cryopreserved allogenic veins are being used clinically and how they are most likely to be expected to fail. Autologous vein bypass grafts are characterized by a series of distinct biological properties that influences their in vivo patency. Current surgical practice ensures that the endothelium of vein grafts is preserved at the time of implantation and that there is minimal damage to the smooth muscle cells. After implantation, the endothelial cells show varying degrees of morphological changes that are maximal within the first 3 days after grafting. In autografts, extensive endothelial denudation does not appear to occur. During the initial grafting period, the smooth muscle cells change from a contractile phenotype to a synthetic phenotype, migrate from the media, proliferate in the intima, and lay down connective tissue. Thereafter, endothelial cell changes regress and the smooth muscle cells return to their contractile phenotype. Perioperative manipulation of vein grafts results in decreased endothelial cell function but preservation of smooth muscle cell responsiveness. Postoperatively endothelial cell-mediated relaxation to acetylcholine is lost and smooth muscle cell contractility is decreased. Within 7 days after implantation, smooth muscle cell contractility returns and, with time, becomes markedly greater than that of the control vein. Endothelium-mediated relaxation to acetylcholine never returns in vein grafts and this loss of endothelial cell function appears to be related to receptor-coupled G-protein defects. Smooth muscle cell contractility remains abnormal. Many of the intimal hyperplastic lesions in vein grafts progress to stenosis or become sites of accelerated atherosclerosis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification and expression of the SOS response, aidB-like, gene in the marine sponge Geodia cydonium: implication for the phylogenetic relationships of metazoan acyl-CoA dehydrogenases and acyl-CoA oxidases

Lysophosphatidic acid (LPA) is an extracellular signaling molecule that can enter the central nervous system following injury or diseases that disrupt the blood-brain-barrier. Using a combination of time-lapse microscopy, immunocytochemistry, and biochemical techniques, we demonstrate that LPA stimulates profound changes in astrocyte morphology that are due to effects on the actomyosin cytoskeleton. Flat astrocytes in primary culture display prominent actin stress fibers. Treatment with the myosin light chain kinase inhibitor, ML-9, causes stress fiber dissolution and dramatic morphology changes including rounding of the cell body and the formation of processes. LPA can stabilize actin stress fibers and inhibit the morphology changes in ML-9-treated cells. Furthermore, this activity is dependent upon activation of the GTP-binding protein Rho as evidenced by the ability of C3 exoenzyme, a specific inhibitor of Rho, to block the effect. Phosphorylation of the regulatory light (RLC) chain initiates conformational changes in myosin II that result in the formation of myosin filaments and the recruitment of actin into contractile stress fibers. LPA-induced stabilization of stress fibers is accompanied by increases in phosphorylation of the RLC of myosin. Furthermore, astrocytes grown on flexible silicone undergo rapid contraction in response to LPA treatment. The forces generated by these cells manifest themselves as increased wrinkling in the silicone. The observed contraction and accompanying increases in regulatory light chain phosphorylation suggest that LPA-induced signaling cascades in astrocytes regulate actin/myosin interactions.     

Immunological identification of candidate proteins involved in regulating active shape changes of outer hair cells

By employing immunological methods, it has been demonstrated that myosin, myosin light chain (MLC) and myosin light chain kinase (MLCK) proteins in outer hair cells (OHC) are immunologically different from isoforms in platelets, smooth muscle and heart muscle, and are probably more related to isoforms found in red blood cells (RBC). Moreover, proteins related to band 3 protein (b3p) and protein 4.1 (p 4.1), ankyrin as well as fodrin and spectrin, but not glycophorin, have been identified in isolated OHCs. Both OHCs and RBC differ from other motile non-muscle cells in their lack of smooth muscle isoforms of actin, their common high levels of spectrin-, ankyrin- and band 3-like proteins, as well as the expression of the 80 kDa protein 4.1 isoform. The data support the notion that motility of OHC may be based upon regulation of the b3p/p 4.1/ankyrin complex, and thus may be reminiscent to the active shape changes in RBC.     

Study of molecular mechanisms of muscle contraction using polarization fluorometry

The review summarizes results of studies on the conformational changes in contractile proteins during muscle contraction. The studies were carried out by polarized fluorescence technique in the UV and visible light. The revealed were alterations of actin and myosin in muscle fiber, taking place at various stages of contractile cycle. Transition from a weak binding state of actomyosin to a strong one was accompanied by F-actin subunit rearrangements, with C- and N-terminals moving relative to the core of thin filament. Myosin light chains and 20-kDa domain of myosin head moved in the same direction as C- and N-terminal regions of actin. The flexibility of actin filaments increased, whereas that of C- and N-terminal regions decreased sharply. Actin-myosin interaction changed dramatically tropomyosin flexibility and caused displacement of the protein relative to C- and N-terminals of actin. Actin structure "freezing" by glutaraldehyde or phalloidin, actin cleavage by subtilisin, as well as actin alteration in denervational atrophy inhibited markedly the intramolecular movement and isometric tension of muscle contraction. Besides, troponin-, caldesmon-, calponin-, and myosin-systems, regulating muscle contraction, modified actomyosin rearrangements in a Ca(2+)-dependent manner. The role of the movement of polypeptide chains in contractile proteins during muscle contraction is discussed.     

Transitions in cell organization and in expression of contractile and extracellular matrix proteins during development of chicken aortic smooth muscle: evidence for a complex spatial and temporal differentiation program

Whereas the understanding of the mechanisms underlying skeletal and cardiac muscle development has been increased dramatically in recent years, the understanding of smooth muscle development is still in its infancy. This paper summarizes studies on the ontogeny of chicken smooth muscle cells in the wall of the aorta and aortic arch-derived arteries. Employing immunocytochemistry with antibodies against smooth muscle contractile and extracellular matrix proteins we trace smooth muscle cell patterning from early development throughout adulthood. Comparing late stage embryos to young and adult chickens we demonstrate, for all the stages analyzed, that the cells in the media of aortic arch-derived arteries and of the thoracic aorta are organized in alternating lamellae. The lamellar cells, but not the interlamellar cells, express smooth muscle specific contractile proteins and are surrounded by basement membrane proteins. This smooth muscle cell organization of lamellar and interlamellar cells is fully acquired by embryonic day 11 (ED 11). We further show that, during earlier stages of embryogenesis (ED3 through ED7), cells expressing smooth muscle proteins appear only in the peri-endothelial region of the aortic and aortic arch wall and are organized as a narrow band of cells that does not demonstrate the lamellar-interlamellar pattern. On ED9, infrequent cells organized in lamellar-interlamellar organization can be detected and their frequency increases by ED10. In addition to changes in cell organization, we show that there is a characteristic sequence of contractile and extracellular matrix protein expression during development of the aortic wall. At ED3 the peri-endothelial band of differentiated smooth muscle cells is already positive for smooth muscle alpha actin (alphaSM-actin) and fibronectin. By the next embryonic day the peri-endothelial cell layer is also positive for smooth muscle myosin light chain kinase (SM-MLCK). Subsequently, by ED5 this peri-endothelial band of differentiated smooth muscle cells is positive for alphaSM-actin, SM-MLCK, SM-calponin, fibronectin, and collagen type IV. However, laminin and desmin (characteristic basement membrane and contractile proteins of smooth muscle) are first seen only at the onset of the lamellar-interlamellar cell organization (ED9 to ED10). We conclude that the development of chicken aortic smooth muscle involves transitions in cell organization and in expression of smooth muscle proteins until the adult-like phenotype is achieved by mid-embryogenesis. This detailed analysis of the ontogeny of chick aortic smooth muscle should provide a sound basis for future studies on the regulatory mechanisms underlying vascular smooth muscle development.     

Role of caveolae in cholesterol transport in arterial smooth muscle cells exposed to lipoproteins in vitro and in vivo

Arterial smooth muscle cells are able to shift between two major differentiated states with distinct morphologic and functional properties, a contractile phenotype and a synthetic phenotype. Recently, it was demonstrated that contractile smooth muscle cells have numerous caveolae and that these specialized regions of the plasma membrane, to a large extent, are lost when the cells are modified into a synthetic phenotype. At the same time, the levels of the cholesterol-binding membrane protein caveolin remained unchanged and caveolin was redistributed from the cell surface to the perinuclear cytoplasm. In the present investigation, electron microscopy was used to study how smooth muscle cells of different phenotypes react to exposure to low-density lipoprotein and other lipoproteins both in vitro and in vivo. Our findings indicate that contractile cells (present early in primary culture and in the media of normal arterial walls) do not accumulate lipids in the cytoplasm and release excess cholesterol by means of plasma membrane caveolae. Extracellularly, the expelled lipids were built into membranous configurations and piled up as myelin-like deposits. In synthetic cells (formed after a few days in primary culture and as a response to arterial injury), lipids gathered in cytoplasmic droplets and increased amounts of membranous inclusions appeared in endosomes and lysosomes. On the other hand, no signs of extracellular discharge of lipids were detected. The results suggest that contractile smooth muscle cells use caveolin and caveolae to free themselves of excess lipoprotein-derived cholesterol and so manage to maintain a balance in the influx and efflux of cholesterol. Synthetic smooth muscle cells show a Golgi-like immunostaining for caveolin but have an insufficient capacity to use this protein to transport cholesterol to the plasma membrane and out of the cell. Cholesterol will then rather be esterified and collect in lipid droplets, eventually leading to foam cell formation if the uptake of lipoprotein continues.     

Airway structure and function in Eisenmenger's syndrome

The responsiveness of airways from patients with Eisenmenger's syndrome (n = 5) was compared with that in airways from organ donors (n = 10). Enhanced contractile responses to cholinergic stimulation were found in airways from patients with Eisenmenger's syndrome. The maximal responses to acetylcholine, carbachol, and parasympathetic nerve stimulation in airway tissue from these patients were 221%, 139%, and 152%, respectively, of the maximal responses obtained in donor tissue. Further, relaxation responses to isoproterenol and levocromakalim were absent (n = 2) or markedly impaired (n = 3) in airways from patients with Eisenmenger's syndrome. This attenuated relaxation response was nonspecific in that it was also absent after vasoactive intestinal peptide, sodium nitroprusside, papaverine, and electrical field application. These observations can most likely be explained by a decrease in intrinsic smooth muscle tone, as precontraction of airways revealed relaxation responses that were equivalent to those obtained in donor tissues. Morphometric analysis of tissues used for the functional studies revealed no differences in the airway dimensions (internal perimeter) or airway wall components (e.g., smooth muscle, cartilage) or total area to explain these observations. Although the mechanism for this observed decrease in intrinsic airway smooth muscle tone is not certain, it may be due to alteration in the substructure of the airway wall or, alternatively, may result from the continued release of depressant factors in the vicinity of the smooth muscle which permanently alters smooth muscle responsiveness.