PubMed Health⌕ Search

Biomedical subjects

T K Borg

Publications and source records attributed to T K Borg.

At least 73 records · Page 4Linked to original sources
PubMed1985

Extracellular matrix components influence the survival of adult cardiac myocytes in vitro.

Calcium-tolerant myocytes were isolated from adult rat hearts by collagenase perfusion and plated on various substrates in serum-free medium and their adhesion to various extracellular matrix (ECM) components was determined. The myocytes attached readily to dishes coated with collagen type IV (C-IV), laminin (LN), and to fetal bovine serum (FBS) in a manner dependent on the concentration of the components. Substantially fewer myocytes adhered to dishes coated with fibronectin (FN) or to uncoated plastic dishes. Cells adhered equally well to dishes coated with C-IV, LN and FBS within 1-4 h. However, when examined after 2 weeks in culture it was found that only C-IV and LN could support survival of the attached myocytes, and when cultured on C-IV or LN the myocytes were spread and had formed a dense monolayer. The actin filaments had at this time reorganized linearly along the long axis of the cell and the myocytes contracted spontaneously. Rabbit antibodies were raised against myocyte membranes and their ability to inhibit attachment to ECM components was studied. Purified IgG inhibited attachment to C-IV, while having only a minor effect on attachment to LN. These data are compatible with the presence of a specific cell surface component(s) that interacts with ECM substrates and influences cell shape and possibly thereby influences cellular functions.

Animals↗
PubMed1985

Alteration of the connective tissue network of striated muscle in copper deficient rats.

The connective tissue network in striated muscle, consisting principally of collagen is arranged in a three dimensional network and is intimately associated with muscle function. Previous studies have shown that animals maintained on a copper-deficient diet undergo myocardial hypertrophy and exhibit cardiovascular lesions such as ventricular aneurysms that eventually rupture. A deficiency of copper in the diet is known to inhibit lysyl oxidase, a metalloenzyme requiring copper as a cofactor and which is also responsible for collagen and elastin crosslinking. Examination by scanning and transmission electron microscopy of skeletal and cardiac muscle from rats maintained on copper-deficient diets showed both gross and microscopic lesions to the connective tissue network. Immunohistochemical staining by light microscopy with antibodies against lysyl oxidase showed that the enzyme was equally present in both control and experimental animals. Fluorescent staining for antibodies against collagen types I and III showed similar results. From these studies we concluded that the collagen secreted during hypertrophy was not crosslinked by lysyl oxidase due to the absence of the copper cofactor. This resulted in the failure of the connective tissue network to transmit and distribute the increased force associated with myocardial hypertrophy and resulted in myocardial aneurysms.

Animals↗
PubMed1984

Interactions of mammalian cells with collagen.

Isolated stationary cells recognize and adhere to immobilized extracellular matrix (ECM) components. These processes are mediated by specific receptor-ligand types of interaction. The formation of cell-ECM contacts influences subsequent cellular behaviour, such as the promotion of cell survival, epithelial cell polarization, and cell differentiation. The binding reaction between cells and collagen is discussed in this paper in terms of findings from studies with two cell systems, adult rat hepatocytes and rat cardiac myocytes. Isolated adult rat hepatocytes adhere to or bind laminin, fibronectin, heparan sulphate and collagen. We have characterized the interaction of hepatocytes with collagen and have isolated a glycoprotein fraction from rat liver membranes that contains collagen-binding components. The ability of rat cardiac myocytes to recognize ECM components depends on the state of cell maturation. Myocytes isolated from neonatal rats adhere to the interstitial collagens (types I-III), to collagen types IV and V, to fibronectin and to laminin. In contrast, myocytes isolated from adult rats bind effectively only to collagen type IV and laminin and bind much less effectively to fibronectin. Furthermore, antibodies raised against neonatal myocyte membranes inhibit the adhesion of both neonatal myocytes and hepatocytes to interstitial collagens, but antibodies raised against adult myocyte membranes lack these effects. These observations indicate that similar collagen-binding molecules are present on such diverse cells as hepatocytes and neonatal myocytes and that these components might be lost during cell maturation.

Animals↗
PubMed1984

Recognition of extracellular matrix components by neonatal and adult cardiac myocytes.

Recognition of extracellular matrix (ECM) components by isolated cardiac myocytes from neonatal (4-5 days postpartum) and adult rats was determined by measuring cell attachment to substrates made of ECM components. The substrates were petri dishes coated with either fibronectin, laminin, native monomers of collagen types I, II, III, IV, and V, denatured collagen, or gels containing reconstituted collagen fibers. Adult myocytes attached efficiently to laminin and type IV collagen, weakly to fibronectin, but not at all to the other types of collagen. Neonatal myocytes attached well to all types of collagen and to fibronectin and laminin. Antibodies raised against surface membranes of neonatal myocytes, adult myocytes, or adult hepatocytes were assayed for their ability to inhibit cell attachment to the various ECM substrates. Antibodies against the surface of neonatal myocytes as well as antibodies against the hepatocyte cell surface inhibited the attachment of neonatal myocytes and hepatocytes to collagen but not to fibronectin. Antibodies against the adult myocyte cell surface did not inhibit the attachment of neonatal myocytes or hepatocytes to ECM components. These results indicate the presence of binding molecules on the surface of neonatal myocytes that are involved in the recognition of collagen at a time when collagen is being secreted and formed into a three-dimensional network that attaches to the cell surface of the myocytes. This recognition and adhesion to collagen occurs by a mechanism independent of fibronectin. The binding molecules for collagen could not be detected on normal adult myocytes isolated at a time when the formation of the collagen network has already been completed.

Aging↗
PubMed1983

The effects of systole on left ventricular blood flow.

Coronary artery flow is complex. Flow in this system is divided into systolic and diastolic. However, systolic flow should be divided into two phases, isovolumetric and the ejection phase, since these two components are determined by completely different parameters. Flow through the myocardium is affected by the close mechanical coupling between myocytes and capillaries effected by the array of collagen struts and their disposition. This latter provides the anatomic arrangement that makes possible the integrated "massaging" effect postulated by Wiggers (26).

Animals↗
PubMed1983

Specific attachment of collagen to cardiac myocytes: in vivo and in vitro.

The formation and attachment of collagen to the sarcolemma of cardiac myocytes were examined in vivo in neonatal rats and hamsters and in vitro in cultures of neonatal rat myocytes. Scanning, transmission, and high-voltage electron microscopy were used to show that the collagen struts attach to specific sites on the sarcolemma just lateral to the Z band of neonatal animals. In vitro, collagen preferentially attaches to distal end of myocytes at a site where internal stress fibers also attach to the sarcolemma. Formation of the collagen struts appeared to be a multistep process involving several components of the extracellular matrix. The role of the collagen struts is involved in the distribution of force generated by muscle contraction.

Animals↗
PubMed1982

Development of the connective tissue network in the neonatal hamster heart.

The formation of the connective tissue network, composed principally of collagen, in the left ventricle of the neonatal hamster heart developed primarily during the first 20 days postpartum. The weave network of the endomysium, which was absent at birth, was visible by 4 days and was similar to that of the adult by 15 days postpartum. Myocyte-myocyte and myocyte-capillary struts formed gradually as the heart underwent physiological hypertrophy. These data were similar to the development of the connective tissue network in the rat except that the myocyte-myocyte struts were more numerous in the hamster. Presumably this is because the hamster has a higher heart rate, which would require more mechanical coupling of the myocytes. Formation of the struts appears to take place at precise areas on the sarcolemma through the interaction of collagenous and noncollagenous components of the extracellular matrix.

Animals↗
PubMed1982

Effects of serum concentration on some growth characteristics of cultured murine parietal yolk sac carcinoma cells.

Murine parietal yolk sac carcinoma cells were examined by scanning and transmission electron microscopy to determine the ultrastructural changes resulting from growth, in vitro, in media containing different serum concentrations. Cells grown in medium supplemented with 10% fetal bovine serum (FBS) formed spherical bodies, were gradually oval with numerous surface microvilli, well-organized microtubules, abundant free polysomes and a well-developed Golgi apparatus. By contrast, cells grown in 1% FBS failed to form multicellular spheres, were generally flattened over the growth surface and lacked the surface and intracellular features demonstrated when cells were grown in 10% serum. These differences could explain the alterations in the glycosylation of secreted glycoprotein associated with culture in the presence of low serum.

Animals↗
PubMed1982

Changes in the distribution of fibronectin and collagen during development of the neonatal rat heart.

Specific antibodies to different types of collagen (I, III, IV and V) and fibronectin were used to investigate the formation of the collagenous connective tissue network in the neonatal rat heart. Immunofluorescence data showed that the staining pattern for fibronectin and Type III collagen was similar as were the patterns for Type I, IV and V collagens. These differences in the staining patterns correlated with previous studies on the development of the connective tissue network and indicated that Type III collagen was the major type of collagen associated with the myocytes. The results of this study showed that by 20 days post-partum the development of the connective tissue network was similar to the adult.

Age Factors↗
PubMed1982

Functional arrangement of connective tissue in striated muscle with emphasis on cardiac muscle.

The presence and arrangement of connective tissue associated with cardiac and skeletal muscle and composed principally of collagen is clearly demonstrable by scanning and high voltage electron microscopy. The basic organization consists of a perimysium composed of bundles of collagen fibers that connect the epimysium to the endomysium. The endomysium has at least 4 components: (1) a dense weave network that surrounds myocytes, (2) myocyte-myocyte collagen struts that connect adjacent myocytes, (3) myocyte-capillary struts that connect capillaries and myocytes, and (4) a complex of single collagen fibers, glycoproteins, and glycosaminoglycans. The amount of collagen in each component varies with the function of the muscle. Different types of skeletal muscles contain different amounts of collagen depending upon the function and composition of the particular muscle. In cardiac muscle the amount of collagen varies with different species. Different regions of the heart show differences in the amount of collagen due to different functional requirements of those regions. Thus, the amount of collagen in atria is different than in the ventricles due to differences in pressure and volume of these components of the heart.

Animals↗
PubMed1981

The collagen matrix of the heart.

Scanning electron microscopy demonstrates an extensive and highly organized network of collagen in the left ventricle of all species examined. This system is arbitrarily divisible into three major components: a collagen weave network that surrounds groups of myocytes; an extensive array of collagen struts measuring 120 to 150 nm in diameter that extend from the basal lamina of a myocyte to the basal laminae of all contiguous myocytes; and an array of similar sized collagen struts that extend from the basal lamina of all capillaries to the basal laminae of all contiguous myocytes. The functions of the individual components of this complicated network are not well-defined. The weave network certainly contributes to the viscous and elastic properties of the heart. Myocyte-to-myocyte struts can prevent slippage of adjacent cells during the cardiac cycle and would ensure equal stretch of adjacent myocytes during diastole. Myocyte to capillary struts may be important in maintaining capillary patency during the early phases of systole. In rats. rabbits and hamsters this entire system is virtually absent at birth and develops rapidly to the adult form by 15 days.

Aging↗
PubMed1981

A freeze-fracture study of avian epiphyseal cartilage differentiation.

The morphological features of avian epiphyseal cartilage have been investigated by freeze-fracture techniques. Progressive changes occurred in both the cells and the matrix during differentiation. Chondrocytes changed in shape from small flattened cells with few, short cellular processes, to enlarged ovoid cells with numerous long processes often associated with extracellular vesicles. In the matrix these vesicles appeared first in the cellular lacunae, then in the extralacunar matrix, becoming larger and more numerous. Large membrane-associated particles (MAPS) were seen on the p faces of the plasmalemma. These became progressively concentrated on and around the cellular processes, with few large MAPS being seen on the e face. Similar distribution of MAPS was seen in the matrix vesicles. Domains of hydrated proteoglycan aggregates were manifest as regular fracture patterns in the extralacunar matrix of the upper regions of the plate. Collagen fibrils progressively increased in size and state of aggregation, often being associated with matrix vesicles and in the end, with long plate-like mineral crystals. These findings, while in basic agreement with patterns observed with TEM, reveal important new features concerning cellular and matrix structure during cartilage differentiation.

Animals↗
PubMed1981

Mechanical and structural correlates of canine pericardium.

We have assessed viscoelastic properties of pericardium within the physiological range of stresses and related mechanical behavior to fiber direction as defined by scanning electron microscopy. Stiffness, stress relaxation, and creep were measured in samples taken from the anterior surface of 14 canine pericardia. Stress-strain relations generally were not exponential; stiffness at a stress of 1 g/mm2 ranged from 12.9 to 239 g/mm2 during stretch and varied both from pericardium to pericardium and with the orientation of the strip within the sample (anisotropy). The strips exhibited hysteretic behavior which was not promotional to rate of strain. Following a rapid increase in stress, creep averaged less than 1% and stress relaxation, 34% in a 30-minute test period. The orientation of the strip with the greatest stiffness was consistent from pericardium to pericardium, and correlated with a layer of collagen fibers oriented along the major axis of te strip.

Animals↗
PubMed1981

Structural basis of ventricular stiffness.

The morphologic component of ventricular stiffness has not been clearly delineated. This stiffness factor varies over wide ranges with the degree of distension, being very low at low volumes and very high at high volumes. It is constant in rats and hamsters from 30 days of age to 17 months, varying no more than 20%, with increases in mass of 4-fold. These parameters alone suggest a complex structure or structures. The ventricular stiffness factor of rats is about twice that of hamsters at all ages. This naturally occurring variation in stiffness of normal hearts from the two species provides an excellent model to examine for morphologic differences that might explain the variation in stiffness of the two ventricles. Hearts from each species from 1 to 7 months of age were examined by light microscopy and scanning and transmission electron microscopy. There is a major difference between the two species in the amount of collagen in the form of 120- to 150-nm. diameter bundles that form a weave around groups of myocytes. This system is far more extensive in rats than hamsters and is the only morphologic difference that can easily explain the divergence in stiffness between the two species.

Age Factors↗
PubMed1980

Morphology of connective tissue in skeletal muscle.

The arrangement and distribution of connective tissue in six different skeletal muscles and smooth muscle was examined by scanning electron microscopy. The endomysial arrangement of collagen was similar in all types of muscle and consisted of three components: (1) myocyte-myocyte connectives; (2) myocyte-capillary connectives; and (3) a weave network of collagen intimately associated with the basal laminae of the myocytes. The perimysium of the different muscles was qualitatively similar but quantitatively dissimilar. The perimysium consisted consisted of large tendon-like bundles of interwoven collagen which connected with the dense weave collagen that surrounded groups of muscles. The arrangement of the collagen in the perimysium and endomysium would explain differences in the mechanical properties of the different muscle. The contribution of the connective tissue to mechanical properties of muscle is discussed.

Animals↗
PubMed1979

The collagen network of the heart.

An extensive collagen skeleton in the myocardium is clearly demonstrable by scanning electron microscopy. This system mechanically connects myocytes to contiguous myocytes, connects myocytes to contiguous capillaries, and is responsible for orienting myocytes into anatomical units. The extent and location of the system involves it in a variety of physical parameters of the heart under both normal and abnormal conditions. The myocyte to myocyte collagen struts may provide for sarcomere alignment from cell to cell, ensure equal stretch of contiguous cells, and prevent slippage of adjacent cells. The numerous myocyte to web network connections would ensure that the entire group of cells function in a consistent fashion. The origin and course of the myocyte to capillary collagen struts could account for capillary patency during systole in the presence of high ventricular wall pressures. The complex web network surrounds groups of myocytes and is mechanically coupled to the contained myocytes. The loose collagen connections between groups easily permits slippage and rearrangement of groups of cells as expected in acute dilation. The web network itself could be the site of some of the viscoelastic properties of the heart.

Animals↗