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Biomedical subjects

A Weisberg

Publications and source records attributed to A Weisberg.

At least 19 recordsLinked to original sources
PubMed2006

Plasminogen activator inhibitor-1 deficiency protects against aldosterone-induced glomerular injury.

This study tests the hypothesis that plasminogen activator inhibitor-1 (PAI-1) contributes to aldosterone-induced renal and cardiac injury. The effects of 12-week aldosterone (2.8 microg/day)/salt (1% drinking water) versus vehicle/salt on renal and cardiac histology and mRNA expression were determined in wild-type (WT) and PAI-1 deficient (PAI-1(-/-)) mice. Systolic blood pressure was similar in aldosterone-infused WT and PAI-1(-/-) mice until 12 weeks, when it was significantly higher in the WT mice. At 12 weeks, urine volume, sodium excretion, and sodium/potassium ratio were similarly increased in the two aldosterone-infused groups. In contrast, urine albumin excretion was greater in aldosterone-infused WT mice (mean+/-s.d.: 699.0+/-873.0 microg/24 h) compared to vehicle-infused WT (23.6+/-9.0 microg/24 h, P=0.003) or aldosterone-infused PAI-1(-/-) mice (131.6+/-110.6 microg/24 h, P=0.007). Aldosterone increased glomerular area to a greater extent in WT (4651+/-577 versus 3278+/-488 microm2/glomerulus in vehicle-infused WT, P<0.001) than in PAI-1(-/-) mice (3713+/-705 microm2/glomerulus, P=0.001 versus aldosterone-infused WT), with corresponding mesangial expansion. Renal collagen content was also increased in aldosterone-infused WT versus PAI-1(-/-) mice. In WT mice, aldosterone increased renal mRNA expression of PAI-1, collagen I, collagen III, osteopontin, fibronectin, monocyte chemoattractant protein-1 (MCP-1), and F4/80 (all P<0.05), but not transforming growth factor beta (TGF-beta). In PAI-1(-/-) mice, aldosterone increased renal expression of collagen I, osteopontin, fibronectin, and MCP-1, and tended to increase collagen III. Renal osteopontin expression was diminished in aldosterone-treated PAI-1(-/-) compared to aldosterone-treated WT mice (P=0.05). Aldosterone induced cardiac hypertrophy but not fibrosis in WT and PAI-1(-/-) mice. PAI-1 contributes to aldosterone-induced glomerular injury.

Albuminuria↗
PubMed2003

[A new tricortical implant].

We wish to introduce a new type of implant intended for use in the posterior maxilla when only 8 mm or less of the resorbed alveolar ridge is present, without the need for sinus lift procedures or ridge augmentation. The implant is called "Excalibur" and will be available in varying lengths with either an internal or external hex. The implant is supported at three points in the cortical bone due to the use of an apically positioned screw, which passes through the implant and the buccal and palatal cortices at 90 degrees to the long axis of the implant. The bicortical screw is inserted via a minimal full thickness flap or through a small incision in the gingiva at the proposed point of placement. The additional stability provided by this screw allows for immediate loading at the time of implant placement. In comparative tests with regular implants, the "Excalibur" was found to be far more resistant to forces applied to the implant resulting in far less stress on the neck of the implant, which was shown on the finite element modeling. Two clinical cases are presented: 1) Excalibur implants were placed in the posterior maxilla and four months after the surgical procedure the permanent prosthetic rehabilitation was completed. 2) Excalibur implants were placed at the time of extraction, with an immediate temporary acrylic bridge. Permanent prosthetic rehabilitation was begun four months later.

Alveolar Bone Loss↗
PubMed2001

Multiple structures of thick filaments in resting cardiac muscle and their influence on cross-bridge interactions.

Based on two criteria, the tightness of packing of myosin rods within the backbone of the filament and the degree of order of the myosin heads, thick filaments isolated from a control group of rat hearts had three different structures. Two of the structures of thick filaments had ordered myosin heads and were distinguishable from each other by the difference in tightness of packing of the myosin rods. Depending on the packing, their structure has been called loose or tight. The third structure had narrow shafts and disordered myosin heads extending at different angles from the backbone. This structure has been called disordered. After phosphorylation of myosin-binding protein C (MyBP-C) with protein kinase A (PKA), almost all thick filaments exhibited the loose structure. Transitions from one structure to another in quiescent muscles were produced by changing the concentration of extracellular Ca. The probability of interaction between isolated thick and thin filaments in control, PKA-treated preparations, and preparations exposed to different Ca concentrations was estimated by electron microscopy. Interactions were more frequent with phosphorylated thick filaments having the loose structure than with either the tight or disordered structure. In view of the presence of MgATP and the absence of Ca, the interaction between the myosin heads and the thin filaments was most likely the weak attachment that precedes the force-generating steps in the cross-bridge cycle. These results suggest that phosphorylation of MyBP-C in cardiac thick filaments increases the probability of cross-bridges forming weak attachments to thin filaments in the absence of activation. This mechanism may modulate the number of cross-bridges generating force during activation.

Actins↗
PubMed2001

Morphology of the frontal operculum: a volumetric magnetic resonance imaging study of the pars triangularis.

OBJECTIVE: Broca's area, which includes the pars triangularis (PTR), is a neuroanatomical region important in speech and language production. Linear measures of the PTR have been found to be asymmetric, with the direction of the asymmetry correlating with language dominance determined by Wada testing. It is unclear, however, whether these linear measurements correlate with volumetric measures, and it is also unknown whether white matter and/or gray matter contribute differentially to these asymmetries. To investigate these issues, volumetric magnetic resonance imaging methodologies were used to measure the PTR in a group of healthy right-handed men (n = 12). There was a significant leftward asymmetry of the PTR using linear and volumetric measures. Linear measures of the left and right hemispheres were highly correlated with volumetric measures. Underlying gray and white matter both contributed to PTR asymmetry. Anatomical boundaries and four configurations (V, U, Y, and J) are discussed with reference to potential interhemispheric differences.

Adult↗
PubMed2000

Characterization of the vaccinia virus H3L envelope protein: topology and posttranslational membrane insertion via the C-terminal hydrophobic tail.

The vaccinia virus H3L open reading frame encodes a 324-amino-acid immunodominant membrane component of virus particles. Biochemical and microscopic studies demonstrated that the H3L protein was expressed late in infection, accumulated in the cytoplasmic viral factory regions, and associated primarily with amorphous material near immature virions and with intracellular virion membranes. Localization of the H3L protein on the surfaces of viral particles and anchorage via the hydrophobic tail were consistent with its extraction by NP-40 in the absence of reducing agents, its trypsin sensitivity, its reactivity with a membrane-impermeable biotinylation reagent, and its immunogold labeling with an antibody to a peptide comprising amino acids 247 to 259. The H3L protein, synthesized in a coupled in vitro transcription/translation system, was tightly anchored to membranes as determined by resistance to Na(2)CO(3) (pH 11) extraction and cytoplasmically oriented as shown by sensitivity to proteinase K digestion. Further studies demonstrated that membrane insertion of the H3L protein occurred posttranslationally and that the C-terminal hydrophobic domain was necessary and sufficient for this to occur. These data indicated that the H3L protein is a member of the C-terminal anchor family and supported a model in which it is synthesized on free ribosomes and inserts into the membranes of viral particles during their maturation.

Animals↗
PubMed2000

Effects of deletion or stringent repression of the H3L envelope gene on vaccinia virus replication.

The C-terminal membrane anchor protein encoded by the H3L open reading frame of vaccinia virus is located on the surfaces of intracellular mature virions. To investigate the role of the H3L protein, we constructed deletion (vH3Delta) and inducible (vH3i) null mutants. The H3L protein was not detected in lysates of cells infected with vH3Delta or vH3i in the absence of inducer. Under these conditions, plaques were small and round instead of large and comet shaped, indicative of decreased virus replication or cell-to-cell spread. The mutant phenotype was correlated with reduced yields of infectious intra- and extracellular virus in one-step growth experiments. The defect in vH3i replication could not be attributed to a role of the H3L protein in virus binding, internalization, or any event prior to late gene expression. Electron microscopic examination of cells infected with vH3Delta or vH3i in the absence of inducer revealed that virion assembly was impaired, resulting in a high ratio of immature to mature virus forms with an accumulation of crescent membranes adjacent to granular material and DNA crystalloids. The absence of the H3L protein did not impair the membrane localization of virion surface proteins encoded by the A27L, D8L, and L1R genes. The wrapping of virions and actin tail formation were not specifically blocked, but there was an apparent defect in low-pH-mediated syncytium formation that could be attributed to decreased virus particle production. The phenotypes of the H3L deletion and repression mutants were identical to each other but differed from those produced by null mutations of genes encoding other vaccinia virus membrane components.

Animals↗
PubMed1998

Relation between crossbridge structure and actomyosin ATPase activity in rat heart.

Cardiac myofilaments contain proteins that regulate the interaction between actin and myosin. In the thick filament, there are several proteins that may contribute to the regulation of the contraction. The myosin binding protein C, or C protein, has 4 sites that can be phosphorylated by a Ca2+-calmodulin-controlled kinase, protein kinase A or protein kinase C. Using electron microscopy and optical diffraction, we examined the structure of thick filaments isolated from rat ventricles with either the alpha or beta isoform of myosin heavy chain (MHC) and the effect of specific phosphorylation of C protein on the structure. In thick filaments with alpha-MHC, crossbridges were clearly visible. Phosphorylation of C protein by protein kinase A extended the crossbridges from the backbone of the filament, changed their orientation, increased the degree of order of the crossbridges, and decreased the flexibility of the crossbridges. Crossbridges in filaments with beta-MHC were less ordered and apparently more flexible. Phosphorylation of C protein in beta-MHC-containing filaments did not extend the crossbridges and did not alter degree of order or flexibility. The relative flexibility of the crossbridges inferred from the optical diffraction pattern correlated well with the rate of ATP hydrolysis by actomyosin. These results suggest that (1) crossbridge flexibility is an important parameter in setting the rate of crossbridge cycling, and (2) C protein-mediated control of the position and flexibility of crossbridges may regulate actomyosin ATPase activity by modifying the kinetics of crossbridge cycling.

Actin Cytoskeleton↗
PubMed1998

Expression and purification of large nebulin fragments and their interaction with actin.

cDNA clones encoding mouse skeletal muscle nebulin were expressed in Escherichia coli as thioredoxin fusion proteins and purified in the presence of 6 M urea. These fragments, called 7a and 8c, contain 28 and 19 of the weakly repeating approximately 35-residue nebulin modules, respectively. The nebulin fragments are soluble at extremely high pH, but aggregate when dialyzed to neutral pH, as assayed by centrifugation at 16,000 x g. However, when mixed with varying amounts of G-actin at pH 12 and then dialyzed to neutral pH, the nebulin fragments are solubilized in a concentration-dependent manner, remaining in the supernatant along with the monomeric actin. These results show that interaction with G-actin allows the separation of insoluble nebulin aggregates from soluble actin-nebulin complexes by centrifugation. We used this property to assay the incorporation of nebulin fragments into preformed actin filaments. Varying amounts of aggregated nebulin were mixed with a constant amount of F-actin at pH 7.0. The nebulin aggregates were pelleted by centrifugation at 5200 x g, whereas the actin filaments, including incorporated nebulin fragments, remained in the supernatant. Using this assay, we found that nebulin fragments 7a and 8c bound to actin filaments with high affinity. Immunofluorescence and electron microscopy of the actin-nebulin complexes verified that the nebulin fragments were reorganized from punctate aggregates to a filamentous form upon interaction with F-actin. In addition, we found that fragment 7a binds to F-actin with a stoichiometry of one nebulin module per actin monomer, the same stoichiometry we found in vivo. In contrast, 8c binds to F-actin with a stoichiometry of one module per two actin monomers. These data indicate that 7a can be incorporated into actin filaments to the same extent found in vivo, and suggest that shorter fragments may not bind actin filaments in the same way as the native nebulin molecule.

Actins↗
PubMed1998

The envelope protein encoded by the A33R gene is required for formation of actin-containing microvilli and efficient cell-to-cell spread of vaccinia virus.

The vaccinia virus (VV) A33R gene encodes a highly conserved 23- to 28-kDa glycoprotein that is specifically incorporated into the viral outer envelope. The protein is expressed early and late after infection, consistent with putative early and late promoter sequences. To determine the role of the protein, two inducible A33R mutants were constructed, one with the late promoter and one with the early and late A33R promoter elements. Decreased A33R expression was associated with small plaques that formed comets in liquid medium. Using both an antibiotic resistance gene and a color marker, an A33R deletion mutant, vA33delta, was isolated, indicating that the A33R gene is not essential for VV replication. The plaques formed by vA33delta, however, were tiny, indicating that the A33R protein is necessary for efficient cell-to-cell spread. Rescue of the large-plaque phenotype was achieved by inserting a new copy of the A33R gene into the thymidine kinase locus, confirming the specific genetic basis of the phenotype. Although there was a reduction in intracellular virus formed in cells infected with vA33delta, the amount of infectious virus in the medium was increased. The virus particles in the medium had the buoyant density of extracellular enveloped viruses (EEV). Additionally, amounts of vA33delta cell-associated extracellular enveloped viruses (CEV) were found to be normal. Immunogold electron microscopy of cells infected with vA33delta demonstrated the presence of the expected F13L and B5R proteins in wrapping membranes and EEV; however, fully wrapped vA33delta intracellular enveloped viruses (IEV) were rare compared to partially wrapped particles. Specialized actin tails that propel IEV particles to the periphery and virus-tipped microvilli (both common in wild-type-infected cells) were absent in cells infected with vA33delta. This is the first deletion mutant in a VV envelope gene that produces at least normal amounts of fully infectious EEV and CEV and yet has a small-plaque phenotype. These data support a new model for VV spread, emphasizing the importance of virus-tipped actin tails.

Actin Cytoskeleton↗
PubMed1997

The A34R glycoprotein gene is required for induction of specialized actin-containing microvilli and efficient cell-to-cell transmission of vaccinia virus.

The mechanisms allowing vaccinia virus to spread from cell to cell are incompletely understood. The A34R gene of vaccinia virus encodes a glycoprotein that is localized in the outer membranes of extracellular virions. The small-plaque phenotype of an A34R deletion mutant was similar to that of mutants with deletions in other envelope genes that fail to produce extracellular vaccinia virions. Transmission electron microscopy, however, revealed that the A34R mutant produced numerous extracellular particles that were labeled with antibodies to other outer-envelope proteins and with protein A-colloidal gold. Fluorescence and scanning electron microscopy indicated that expression of the A34R protein was necessary for detection of vaccinia virus-induced actin tails, which provide motility to the intracellular enveloped form of vaccinia virus, and of virus-tipped specialized microvilli that project from the cell. The ability of vaccinia virus-infected cells to form syncytia after a brief exposure to a pH below 6, known as fusion from within, failed to occur in the absence of expression of the A34R protein; nevertheless, purified A34R- virions were capable of mediating low-pH-induced fusion from without. The present study provides genetic and microscopic evidence for the involvement of a specific viral protein in the formation or stability of actin-containing microvilli and for a role of these structures in cell-to-cell spread rather than in formation of extracellular virions.

Actins↗
PubMed1996

Alteration of myosin cross bridges by phosphorylation of myosin-binding protein C in cardiac muscle.

In addition to the contractile proteins actin and myosin, contractile filaments of striated muscle contain other proteins that are important for regulating the structure and the interaction of the two force-generating proteins. In the thin filaments, troponin and tropomyosin form a Ca-sensitive trigger that activates normal contraction when intracellular Ca is elevated. In the thick filament, there are several myosin-binding proteins whose functions are unclear. Among these is the myosin-binding protein C (MBP-C). The cardiac isoform contains four phosphorylation sites under the control of cAMP and calmodulin-regulated kinases, whereas the skeletal isoform contains only one such site, suggesting that phosphorylation in cardiac muscle has a specific regulatory function. We isolated natural thick filaments from cardiac muscle and, using electron microscopy and optical diffraction, determined the effect of phosphorylation of MBP-C on cross bridges. The thickness of the filaments that had been treated with protein kinase A was increased where cross bridges were present. No change occurred in the central bare zone that is devoid of cross bridges. The intensity of the reflections along the 43-nm layer line, which is primarily due to the helical array of cross bridges, was increased, and the distance of the first peak reflection from the meridian along the 43-nm layer line was decreased. The results indicate that phosphorylation of MBP-C (i) extends the cross bridges from the backbone of the filament and (ii) increases their degree of order and/or alters their orientation. These changes could alter rate constants for attachment to and detachment from the thin filament and thereby modify force production in activated cardiac muscle.

Animals↗
PubMed1996

Effect of endothelin-1 on actomyosin ATPase activity. Implications for the efficiency of contraction.

Endothelin is a powerful inotropic peptide that increases isometric force in isolated papillary muscle and the extent of shortening in isolated single cardiac myocytes. Its mechanism of action has been variously attributed to increased Ca2+ activation, increased Ca2+ sensitivity of the contractile proteins, and increased intracellular pH, but the physiological function of the changes in cardiac performance remains obscure. In this study, the effects of endothelin-1 on both force development and the kinetics of contraction have been examined. Isometric force, actomyosin ATPase activity, and unloaded shortening velocity were measured. The effects were dose dependent. From 1 to 50 pmol/L endothelin-1 did not alter force development in isolated trabeculae with intact endothelial cells, but actomyosin ATPase activity was increased. Between 100 pmol/L and 10 nmol/L endothelin-1 raised isometric force, decreased actomyosin ATPase activity, and decreased unloaded shortening velocity. The reduction in ATPase activity was progressively enhanced as sarcomere length was increased from 1.9 t0 2.4 microns. These results indicate that the effects of endothelin-1 on the force of contraction and the rate of ATP hydrolysis are not tightly coupled and are changed in the opposite directions by endothelin-1 over most of its effective dose-range. This raises the possibility that endothelin-1 may increase the economy of contraction. A novel function of endothelin may be the modulation of the efficiency of contraction, particularly when increased preload raises the contractile work of the heart.

Adenosine Triphosphate↗
PubMed1995

Endothelin regulation of cardiac contractility in absence of added endothelin.

Endothelin has a positive inotropic effect on cardiac muscle, but its role in the regulation of contraction in cardiac tissue is not clear, inasmuch as there has been no demonstration of endothelin regulation of contractility in the absence of added endothelin. To address this question, the changes in contractility of isolated rat ventricular trabeculae produced by endothelin and by BQ-123, an endothelin receptor A antagonist, were measured in tissues with different levels of contractility resulting from bathing the tissues for different lengths of time. The effect of endothelin depended on the extent to which tension had declined from its peak level: the greater the decline, the larger the increase in developed force produced by endothelin. The effect of BQ-123 also depended on the extent to which force had declined. The effects of the addition of endothelin or BQ-123 indicate the presence of substantial regulation of contractility due to basal secretion of endothelin: the degree of endothelin activity is greater in cardiac tissue generating more tension. Damage to the endocardial endothelium from a brief exposure to Triton X-100 reduced the response to BQ-123. The response to BQ-123 depends on the number of functioning endothelial cells. From the extent of the effect of endothelin or BQ-123, it appears that as much as 50% of total force-generating capacity of the tissue is sensitive to endothelin produced by the endothelial cells in the isolated heart. This stimulation of contractility is gradually lost in the isolated cardiac tissue, contributing to the progressive decline in developed force with time.

Animals↗
PubMed1994

cAMP can raise or lower cardiac actomyosin ATPase activity depending on alpha-adrenergic activity.

Adenosine 3',5'-cyclic monophosphate (cAMP) or beta-adrenergic stimulation has been shown to increase actomyosin adenosinetriphosphatase (ATPase) activity in cardiac muscle. Because the major catecholamine transmitters have both alpha- and beta-adrenergic activity, the possibility of a role for alpha-adrenergic stimulation in the regulation of ATPase activity has been investigated. Histochemical measurement of actomyosin ATPase activity in quickly frozen rat hearts has been used as the assay of enzymatic function of the contractile proteins. The dose-response curve of ATPase activity to cAMP shows an increase in ATPase activity at a threshold concentration of 0.01 microM, a peak effect at 0.5-1.0 microM, and a decline beyond 1.5 microM to a level below control at 10 microM cAMP. Kinetic studies varying ATP concentration from 0.5 to 10 mM indicated the existence of multiple forms of actomyosin ATPase activity in the absence of cAMP and only one form with a higher maximum velocity in the presence of 1 microM cAMP. Apparently cAMP raises the enzymatic activity of the individual actomyosin molecule rather than increasing the number of active molecules. The addition of an alpha-adrenergic blocker had no significant effect in the absence of added cAMP, but in the presence of the cyclic nucleotide, 1 microM prazosin always produced a negative effect on ATPase activity. Over the entire range of 0.01-10 microM, cAMP lowered ATPase activity when the alpha-adrenergic antagonist was present. The integrity of the cAMP regulatory system was sensitive to the tissue oxygen tension at the time the heart was quickly frozen. At certain oxygen tension, the stimulatory component of the cAMP regulation was observed without any inhibitory component, suggesting that there are two relatively independent parts of the regulatory mechanism, an inhibitory and a stimulatory. In the presence of gamma-labeled [32P]ATP, 32P was incorporated into several proteins, including the inhibitory subunit of troponin (TNI), C protein, and the regulatory light chain of myosin. cAMP (1 microM) caused an increase in 32P labeling of TNI and C protein. The addition of prazosin with cAMP caused a decrease in the overall level of phosphorylation with specific dephosphorylation of C protein and TNI, the former to a degree similar to the decrease in actomyosin ATPase activity, the latter to a greater degree. These results indicate that alpha-adrenergic activity modulates the balance between kinase and phosphatase activity in the presence of cAMP, probably by inhibiting phosphatase activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenergic alpha-Agonists↗
PubMed1994

Endothelial cell storage and release of endothelin as a cardioregulatory mechanism.

Coronary vascular endothelial cells release substances into the coronary circulation that modify the contractile system of cardiac myocytes, and cardiac myocytes may release factors that modulate the secretion of cardioregulatory substances by endothelial cells. This regulatory loop is sensitive to the rate of coronary flow and tissue oxygen tension. In the present study, coronary venous effluent from isolated perfused hearts and the contents of the coronary vascular endothelial cells have been collected, the latter by disrupting the cells with coronary perfusion at high pressure. The relative amounts of upregulating and downregulating factors in both collections have been estimated by assaying their effects on the contractility of isolated cardiac trabeculas. The amount of upregulating factor stored in the endothelial cells is sensitive to the rate of coronary flow just before disruption of the cells. The quantity of endothelin in the coronary venous effluent and in the vascular endothelial cell contents was measured by radioimmunoassay and compared with the degree of upregulation of contractility produced by the two types of solutions. Upregulation was never produced in the absence of endothelin. The extent of the increase in contractility that was observed with endothelial cell contents correlated with the concentration of endothelin and was approximately the same as the increase in contractility from similar concentrations of endothelin added to standard Krebs' solution. The amount of the increase in contractility from coronary effluent could be accounted for by the concentration of endothelin in the effluent with the additional presence of some downregulating factor as well. The endothelin antagonist BQ123 inhibited the upregulation from coronary perfusate. It appears that endothelin alone can account for all of the upregulation of contractility produced by the vascular endothelial cells. Coronary flow, probably through shear forces, seems to regulate the production of endothelin possibly from an inactive precursor. Tissue oxygen tension appears to modulate the rate of release of the endothelin from endothelial cells though substances released by cardiac myocytes or other cells in the tissue. The downregulating factor is stored to a much smaller extent.

Animals↗
PubMed1993

Endothelial cells are required for the cAMP regulation of cardiac contractile proteins.

The contractile proteins in mammalian cardiac muscle are regulated by a cAMP-dependent reaction that alters the activity of the actomyosin ATPase. The ATPase activity of cardiac actomyosin has also been shown to depend on factors released by small arteries in the myocardial tissue. Endothelial cells have been implicated in the regulation of the contractile force developed by isolated cardiac tissue. To determine whether endothelial cells are required for the cAMP-dependent regulation of the contractile proteins, the effect of cAMP on the actomyosin ATPase activity was measured in cryostatic sections of isolated, quickly frozen rat ventricular trabeculae. In half of the trabeculae, the endocardial endothelial cells had been damaged by a 1-sec exposure to 0.5% Triton X-100. In trabeculae with intact endothelial cells, cAMP increased actomyosin ATPase activity toward an apparently maximum value. In trabeculae with damaged endothelial cells, cAMP did not change actomyosin ATPase activity. The coronary venous effluent from an isolated heart has already been shown to modify the maximum isometric force developed by an isolated trabecula. The extent to which the force of the isolated trabecula is changed by the coronary venous effluent is closely related to the degree to which cAMP has up-regulated the actomyosin ATPase activity in the isolated heart donating the coronary effluent: the greater the degree of up-regulation of ATPase activity, the greater the increase in force produced by the effluent. These results indicate that endothelial cells are required for the cAMP-dependent regulation of cardiac contractile proteins to function, and these results further suggest that the myocardium autoregulates by modulating the cAMP regulation of contractile proteins with endothelial-derived factors.

Animals↗
PubMed1993

Cardiac endothelial cells modulate contractility of rat heart in response to oxygen tension and coronary flow.

The aim of this study was to determine if endothelial cells in the heart release substances into the coronary perfusion medium that modify the contractility of myocardial cells. To assay the effects on the contractility of cardiac muscle of fluid that has passed through the coronary vasculature, a new method has been developed based on the cascade principle used to study vascular smooth muscle function. The coronary venous effluent from an isolated perfused working heart was collected periodically, and after reoxygenation it was used as the bathing medium for trabeculae isolated from the endocardial surface of another heart. The coronary venous effluent changed the contraction of the isolated trabeculae. The amplitude and the direction of the change depended on the degree of oxygen saturation of the coronary effluent before it was reoxygenated and the rate of coronary flow at the time the effluent was collected. The response of the trabecula to the coronary effluent was substantially altered by damaging the endocardial endothelium with a 1-second exposure to 0.5% Triton X-100 in Krebs' solution. It was completely eliminated by damaging endothelial cells in both the perfused heart producing the effluent and the trabecula on which the effluent was assayed. Therefore, endothelial cells are required for the presence of cardioactive substances in the coronary effluent. The production of a labile endothelium-derived upregulating (positively inotropic) factor and a more stable endothelium-derived downregulating (negatively inotropic) factor has been demonstrated and appears to account for all of the changes in myocardial contractility produced by the coronary effluent. Neither of the endothelium-derived substances demonstrated in the isolated perfused heart is nitric oxide or endothelin. The concentration of the endothelium-derived upregulating factor is sensitive to oxygen tension, whereas the concentration of the endothelium-derived downregulating factor is sensitive to the rate of coronary flow but not oxygen tension. The coronary effluent appears to contain substances that stimulate secretion by the endothelial cells (preendothelial factors) as well as substances that have been produced by the endothelial cells (endothelial factors). The results indicate that during the passage of perfusion medium through the coronary vasculature upregulating and downregulating factors are added to the perfusate in relative concentrations that depend at least in part on local tissue PO2 and the rate of coronary flow. In the intact heart, this mechanism could operate to maintain balance between energy supply and work performed.

Animals↗