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PubMed2006

Determination of the big head carp myofibrillar (Aristichthys nobilis) adenosine triphosphatase activity by ion chromatography.

A method for the determination of adenosine triphosphatase (ATPase) activity of myofibrils of big head carp by using ion chromatography was introduced. Adenosine triphosphate (ATP), adenosine diphosphate (ADP) and orthophosphate (Pi) were separated completely. Recoveries for ATP, ADP and Pi were 98+/-5%, 97+/-4% and 98+/-5%, respectively. Pi liberated from ATP during reaction was monitored by ion chromatography using the suggested method. This method was applicable to the determination of myofibrils ATPase activity for quick quality evaluation of surimi.

Adenosine Triphosphatases↗
PubMed2006

Cytoplasmic gamma-actin is not required for skeletal muscle development but its absence leads to a progressive myopathy.

Nonmuscle gamma(cyto)-actin is expressed at very low levels in skeletal muscle but uniquely localizes to costameres, the cytoskeletal networks that couple peripheral myofibrils to the sarcolemma. We generated and analyzed skeletal muscle-specific gamma(cyto)-actin knockout (Actg1-msKO) mice. Although muscle development proceeded normally, Actg1-msKO mice presented with overt muscle weakness accompanied by a progressive pattern of muscle fiber necrosis/regeneration. Functional deficits in whole-body tension and isometric twitch force were observed, consistent with defects in the connectivity between muscle fibers and/or myofibrils or at the myotendinous junctions. Surprisingly, gamma(cyto)-actin-deficient muscle did not demonstrate the fibrosis, inflammation, and membrane damage typical of several muscular dystrophies but rather presented with a novel progressive myopathy. Together, our data demonstrate an important role for minimally abundant but strategically localized gamma(cyto)-actin in adult skeletal muscle and describe a new mouse model to study the in vivo relevance of subcellular actin isoform sorting.

Actins↗
PubMed2003

The muscle ankyrin repeat proteins: CARP, ankrd2/Arpp and DARP as a family of titin filament-based stress response molecules.

CARP, ankrd-2/Arpp, and DARP, are three members of a conserved gene family, referred to here as MARPs (muscle ankyrin repeat proteins). The expression of MARPs is induced upon injury and hypertrophy (CARP), stretch or denervation (ankrd2/Arpp), and during recovery following starvation (DARP), suggesting that they are involved in muscle stress response pathways. Here, we show that MARP family members contain within their ankyrin repeat region a binding site for the myofibrillar elastic protein titin. Within the myofibril, MARPs, myopalladin, and the calpain protease p94 appear to be components of a titin N2A-based signaling complex. Ultrastructural studies demonstrated that all three endogenous MARP proteins co-localize with I-band titin N2A epitopes in adult heart muscle tissues. In cultured fetal rat cardiac myocytes, passive stretch induced differential distribution patterns of CARP and DARP: staining for both proteins was increased in the nucleus and at the I-band region of myofibrils, while DARP staining also increased at intercalated discs. We speculate that the myofibrillar MARPs are regulated by stretch, and that this links titin-N2A-based myofibrillar stress/strain signals to a MARP-based regulation of muscle gene expression.

Amino Acid Motifs↗
PubMedDate not supplied

Local anesthetic myotoxicity.

Skeletal muscle toxicity is a rare and uncommon side effect of local anesthetic drugs. Intramuscular injections of these agents regularly result in reversible myonecrosis. The extent of muscle damage is dose dependent and worsens with serial or continuous administration. All local anesthetic agents that have been examined are myotoxic, whereby procaine produces the least and bupivacaine the most severe muscle injury.The histologic pattern and the time course of skeletal muscle injury appear rather uniform: hypercontracted myofibrils become evident directly after injection, followed by lytic degeneration of striated muscle sarcoplasmic reticulum, and by myocyte edema and necrosis over the next 1 to 2 days. Myoblasts, basal laminae, and connective tissue elements remain intact in most cases, which permits muscular regeneration within 3 to 4 weeks. Subcellular pathomechanisms of local anesthetic myotoxicity are still not understood in detail. Increased intracellular Ca2+ levels appear to be the most important element in myocyte injury; since denervation, inhibition of sarcolemmal Na+ channels, and direct toxic effects on myofibrils have been excluded as sites of action. In this respect, the quantitative impact of further mitochondria-mediated pathways--at least in bupivacaine toxicity--is still to be established. Although experimental myotoxic effects are impressively intense and reproducible, only a few case reports of myotoxic complications in patients after local anesthetic administrations have been published. In particular, the occurrence of clinically relevant myopathy and myonecrosis has been described after continuous peripheral blocks, infiltration of wound margins, trigger point injections, and peri- and retrobulbar blocks.

Anesthetics, Local↗
PubMed2006

Caffeic acid phenethyl ester prevents cadmium-induced cardiac impairment in rat.

Caffeic acid phenethyl ester (CAPE), a flavonoid like compound, is one of the major components of honeybee propolis. It was found to be a potent free radical scavenger and antioxidant recently. The aim of this study was to examine the effect of CAPE on cadmium (Cd)-induced hypertension and cardiomyopathy in rats. In particular, nitric oxide (NO) may contribute to the pathophysiology of Cd induced cardiac impairment. Malondialdehyde (MDA, an index of lipid peroxidation) levels and nitric oxide (NO, a vasodilator) levels were used as markers Cd-induced cardiac impairment and the success of CAPE treatment. Also, the findings have been supported by the histopathologic evidences. The rats were randomly divided into three experimental groups each (12), as follows: the control group, Cd-treated group (Cd) and Cd plus CAPE-treated group (Cd+CAPE). CdCl(2) in 0.9% NaCl was administrated intraperitoneally (i.p.) with a dose of 1mg/kg/day. CAPE was co-administered i.p. a dose of 10 microM/kg for 15 days. Hypertension was found to be induced by intraperitoneal administration of Cd in a dose of 1mg/kg/day on the measurements taken 15 days later. MDA levels were increased (p<0.001) in cardiac tissue and NO levels were decreased (p<0.05) in serum in the Cd group than those of the control group had. On the other hand, there was a slight difference (increase) in MDA levels in the Cd+CAPE group than the ones in the control group (p<0.003). In addition, MDA levels were decreased and NO levels were increased in the Cd+CAPE group compared with the Cd group (p<0.001, p<0.0001, respectively). As a result, treatment with CAPE significantly reversed the increased lipid peroxidation (LPO) product, MDA, and decreased NO levels in Cd treated animals. In the histopathologic examination, a significant hypertrophy in atrial and ventricular myofibrils was observed in only Cd administered group, in comparison with the control group. There was no statistically significant difference between the CAPE given and control groups by means of atrial and ventricular myofibril diameters. In conclusion, the underlying mechanism of the myocardial hypertrophy may be related to hypertension due to inhibition of NO production in the vessels, and CAPE has a protective effect on Cd-induced hypertension mediated cardiac impairment in the rats.

Animals↗
PubMed2006

Unusual splicing events result in distinct Xin isoforms that associate differentially with filamin c and Mena/VASP.

Filamin c is the predominantly expressed filamin isoform in striated muscles. It is localized in myofibrillar Z-discs, where it binds FATZ and myotilin, and in myotendinous junctions and intercalated discs. Here, we identify Xin, the protein encoded by the human gene 'cardiomyopathy associated 1' (CMYA1) as filamin c binding partner at these specialized structures where the ends of myofibrils are attached to the sarcolemma. Xin directly binds the EVH1 domain proteins Mena and VASP. In the adult heart, Xin and Mena/VASP colocalize with filamin c in intercalated discs. In cultured cardiomyocytes, the proteins also localize in the nonstriated part of myofibrils, where sarcomeres are assembled and an extensive reorganization of the actin cytoskeleton occurs. Unusual intraexonic splicing events result in the existence of three Xin isoforms that associate differentially with its ligands. The identification of the complex filamin c-Xin-Mena/VASP provides a first glance on the role of Xin in the molecular mechanisms involved in developmental and adaptive remodeling of the actin cytoskeleton during cardiac morphogenesis and sarcomere assembly.

Alternative Splicing↗
PubMed1999

Pathogenesis of dilated cardiomyopathy: molecular, structural, and population analyses in tropomodulin-overexpressing transgenic mice.

Dilated cardiomyopathy is characterized by decreased contractile function and loss of myofibril organization. Previously unexplored structural and molecular events that precede and initiate dilation can now be studied in tropomodulin-overexpressing transgenic (TOT) mice exhibiting progressive dilated cardiomyopathy. Onset of dilation did not correspond to a change in transgene expression levels, which were more than threefold above normal at birth and remained elevated throughout postnatal life. Similarly, mitogen-activated protein kinase activation (p38, ERK1/ERK2, JNK1/JNK2) was not associated with dilation. In contrast, calcineurin was activated before dilation, presumably due to doubling of intracellular diastolic calcium levels in TOT cardiomyocytes. Amplitude of systolic calcium transients was greatly increased as well, demonstrating the novel and unique calcium handling profile of TOT cardiomyocytes. Loss of myofibril organization was not apparent by confocal microscopy until over 1 week after birth, although neonatal sarcomeric abnormalities were revealed by ultrastructural analysis. Rapid postnatal increases in heart:body weight ratio at 1.5 weeks were followed by two waves of mortality between 2 and 3 weeks after birth coincident with maturational stress. Ultimately, TOT pathogenesis is a compensatory response to altered sarcomeric structure driven by calcineurin activation within days after birth, making TOTs an excellent paradigm for studying the role of calcium overload in dilated cardiomyopathy.

Animals↗
PubMed1982

Muscle diffraction theory. Relationship between diffraction subpeaks and discrete sarcomere length distributions.

A theoretical discussion is presented that describes the diffraction on monochromatic light by a three-dimensional sarcomere array having the following properties. The basic repetitive diffracting unit is the sarcomere. The contiguous arrangement of physically attached serial sarcomeres in the myofibril is contained within the model so that relative position of sarcomeres depend upon the lengths of intervening ones. Sarcomere length is described by a distribution function. This function may be discrete or continuous and contain one or more subpopulations. Two arrangements of sarcomeres are considered: (a) when sarcomeres of different lengths are arranged randomly in myofibrils the amplitude and width of mth order (m greater than or equal to 1) peaks and associated secondary diffraction maxima decrease and increase monotonically, respectively, as the standard deviation of the length distribution increases. No subpeaks are present regardless of the number of subpopulations within the distribution function. This behavior is shown to follow from the dependence of sarcomere position on the length of intervening sarcomeres. (b) When sarcomeres belonging to the same length subpopulation are arranged in serial contiguous fashion to form domains and more than one length subpopulation is present, then mth order diffraction peaks split to form subpeaks. The theoretical basis for this behavior is developed for the first time and may explain the subpeaks evident in diffraction patterns from cardiac and skeletal muscle.

Light↗
PubMed1998

Force regulation by Ca2+ in skinned single cardiac myocytes of frog.

Atrial and ventricular myocytes 200 to 300 microm long containing one to five myofibrils are isolated from frog hearts. After a cell is caught and held between two suction micropipettes the surface membrane is destroyed by briefly jetting relaxing solution containing 0.05% Triton X-100 on it from a third micropipette. Jetting buffered Ca2+ from other pipettes produces sustained contractions that relax completely on cessation. The pCa/force relationship is determined at 20 degrees C by perfusing a closely spaced sequence of pCa concentrations (pCa = -log[Ca2+]) past the skinned myocyte. At each step in the pCa series quick release of the myocyte length defines the tension baseline and quick restretch allows the kinetics of the return to steady tension to be observed. The pCa/force data fit to the Hill equation for atrial and ventricular myocytes yield, respectively, a pK (curve midpoint) of 5.86 +/- 0.03 (mean +/- SE.; n = 7) and 5.87 +/- 0.02 (n = 18) and an nH (slope) of 4.3 +/- 0.34 and 5.1 +/- 0.35. These slopes are about double those reported previously, suggesting that the cooperativity of Ca2+ activation in frog cardiac myofibrils is as strong as in fast skeletal muscle. The shape of the pCa/force relationship differs from that usually reported for skeletal muscle in that it closely follows the ideal fitted Hill plot with a single slope while that of skeletal muscle appears steeper in the lower than in the upper half. The rate of tension redevelopment following release restretch protocol increases with Ca2+ >10-fold and continues to rise after Ca2+ activated tension saturates. This finding provides support for a strong kinetic mechanism of force regulation by Ca2+ in frog cardiac muscle, at variance with previous reports on mammalian heart muscle. The maximum rate of tension redevelopment following restretch is approximately twofold faster for atrial than for ventricular myocytes, in accord with the idea that the intrinsic speed of the contractile proteins is faster in atrial than in ventricular myocardium.

Animals↗
PubMedDate not supplied

Qualitative and quantitative changes in the ultrastructure of the dog heart after temporary ischaemia and coronary reperfusion.

A total ischaemia of one area of the myocardium was produced by ligature of a coronary artery in dogs. After 30 min, 1 hr, 2 hrs, and 4 hrs the ligature was loosened and the artery was for 1--2 hrs reperfused up to 4--7 days. At the end of the ischaemia and after reperfusion the ultrastructure of the myocardium was qualitatively and morphometrically investigated. The findings concerned: loss of glycogen (partly glycogen accumulation), mitochondrial swellings and fusions and development of megamitochondria, loss of cristae, rupture of the mitochondrial outer membranes, relaxation or supercontraction of the myofibrils, vesicular and vacuolar changes of the sarcoplasmic reticulum, oedema of the sarcoplasm, rupture of the sarcolemma. No significant differences of the quantitative parameters could be observed during the ischaemia from 30 min to 4 hrs: myofibrils 53.65--59.74%, mitochondria 26.51--33.59%, sarcoplasm 8.22--11.86%, sarcoplasmic reticulum 1.41--2.63%, lipofuscin 0.05--0.87%, lipids 0.01--0.10%. In comparing the data of the single animals we could determine significant differences between some parameters at the ends of the ischaemic phase and of the reperfusion phase, but as far as the findings are concerned both increases and decreases could be observed. The investigations show that the limit of the reversibility of damages in myocardial cells is about 45 min; in special cases a longer survival time may be taken into account. Reperfusion has different, though not always positive, effects.

Animals↗
PubMed1995

Regulated expression of a contractile protein gene correlates with recovery of contractile function after reversible metabolic inhibition in cultured myocytes.

Little is known of the relation between recovery of contraction and the regulation of contractile protein gene expression in ventricular myocytes after severe ATP depletion. We have examined alterations in activation of an MLC-2 luciferase fusion gene in cultured neonatal rat ventricular myocytes produced by exposure to 2 mM Na CN and 20 mM 2-deoxyglucose, and after recovery is serum or serum free medium. The effects of metabolic inhibition followed by recovery on expression on an RSV-luciferase activity were also investigated. Myocytes were co-transfected with a CMV beta-galactosidase fusion gene, and luciferase activities were normalized relative to beta-galactosidase activity to control for transfection efficiency. Two hours of metabolic inhibition produced significant cell injury, as documented by disorganization of myofilaments, and reduction in luciferase and beta-galactosidase activity within transfected cells. Cells allowed to recover for 48 h in serum free hormone supplemented medium showed a further decline in corrected luciferase activity, consistent with a marked reduction in MLC-2 gene transcription. Cells recovered from severe metabolic inhibition in serum free medium also showed failure to redevelop contractile activity, and failure of redevelopment of organized myofibrils. In contrast, myocytes exposed to serum during the 48 h recovery period had a marked increase in luciferase activity, resumed contractile activity and re-established organized myofilaments. There were no significant differences between RSV luciferase activities in cells recovered in serum versus serum free media. In ventricular myocytes in which contraction was inhibited by exposure to 10 microM verapamil, MLC-2 luciferase activity declined by 87%. However, even when contractile activity was inhibited by exposure to verapamil during recovery from metabolic inhibition, exposure to serum containing medium caused a significantly greater increase in MLC-2 luciferase activity than did serum free medium. Thus, the effects of serum on MLC-2 gene expression were not solely due to an effect of serum on recovery of contractile activity. Verapamil had no consistent effect on expression of RSV luciferase. These results suggest that expression of the MLC-2 gene is markedly reduced following recovery from severe metabolic inhibition, an effect largely due to cessation of myocyte contractile activity. Resupply of growth factors present in fetal calf serum reactivate expression of this gene, and this is associated with resumption of contractile activity and redevelopment of organized myofibrils. These results suggest that reactivation of contractile protein gene expression during recovery from metabolic inhibition may be beneficial in allowing cells to recover from this insult.

Analysis of Variance↗
PubMed2003

The complete mouse nebulin gene sequence and the identification of cardiac nebulin.

Nebulin is a giant (M(r) 750-850kDa), modular sarcomeric protein proposed to regulate the assembly, and to specify the precise lengths of actin (thin) filaments in vertebrate skeletal muscles. Nebulin's potential role as a molecular template is based on its structural and biochemical properties. Its central approximately 700kDa portion associates with actin along the entire length of the thin filament, its N-terminal region extends to thin filament pointed ends, and approximately 80kDa of its C-terminal region integrates within the Z-line lattice. Here, we determined the exon/intron organization of the entire mouse nebulin gene, which contains 165 exons in a 202kb segment. We identified 16 novel exons, 15 of which encode nebulin-repeat motifs (12 from its central region and 3 from its Z-line region). One novel exon shares high sequence homology to the 20 residue repeats of the tight-junction protein, ZO-1. RT-PCR analyses revealed that all 16 novel exons are expressed in mouse skeletal muscle. Surprisingly, we also amplified mRNA transcripts from mouse and human heart cDNA using primers designed along the entire length of nebulin. The expression of cardiac-specific nebulin transcripts was confirmed by in situ hybridization in fetal rat cardiomyocytes and in embryonic Xenopus laevis (frog) heart. On the protein level, antibodies specific for skeletal muscle nebulin's N and C-terminal regions stained isolated rat cardiac myofibrils at the pointed and barbed ends of thin filaments, respectively. These data indicate a conserved molecular layout of the nebulin filament systems in both cardiac and skeletal myofibrils. We propose that thin filament length regulation in cardiac and skeletal muscles may share conserved nebulin-based mechanisms, and that nebulin isoform diversity may contribute to thin filament length differences in cardiac and skeletal muscle.

Amino Acid Sequence↗
PubMed1983

An in vitro study of the interactions of skeletal muscle M-protein and creatine kinase with myosin and its subfragments.

Two proteins reported to be located in the M-band of skeletal muscle are M-protein (Mr 160,000) and creatine kinase (Mr 83,000). We have isolated and purified these proteins from adult chicken pectoralis muscle, and have studied their in vitro interactions with myosin, heavy meromyosin, light meromyosin and subfragment-2 in order to obtain a fuller understanding of the role these proteins play in the M-band of skeletal muscle. Experiments using the techniques of analytical ultracentrifugation, affinity chromatography and electron microscopy were carried out near physiological pH and ionic strength, under which conditions the M-band proteins are known to be firmly bound to the myofibril in situ. The results of our studies indicate that such interactions are either weak or absent in vitro. Discrepancies between our results and those from several other studies are discussed. We conclude that additional components may be required in order to observe interactions in vitro which are similar to those present in the intact myofibril.

Animals↗
PubMed2002

"Cap disease"--a failure in the correct muscle fibre formation.

Four unrelated patients are reported with muscle hypotonia, weakness, skeletal dysmorphism and respiratory insufficiency since childhood. Muscle tissues were found to contain a number of muscle fibres with abnormal structure. Peripherally located structures such as a cap lacking in ATP-ase and fast myosin activity, rich in desmin, tropomyosin and alpha-actinin consisted of abnormally arranged myofibrils. The position of the peripherally situated myofibrils, as well as their abnormal sarcomere pattern, seems to point to an error in fusion and muscle protein synthesis. Whether our cases of congenital myopathy with cap structures are of hereditary origin or of a sporadic type remains unknown, so far. It seems that the result of our study, as well as data presented in the literature, allows us to divede cap disease into two forms: fatal and nonfatal. The morphological changes in the muscle fibres are identical in all the presented cases but the number of muscle fibres with cap structures is much higher in the fatal form.

Adolescent↗
PubMed1999

Decreased expression of myotonic dystrophy protein kinase and disorganization of sarcoplasmic reticulum in skeletal muscle of myotonic dystrophy.

Pathological expression of myotonic'dystrophy protein kinase (DMPK) in skeletal muscle of myotonic dystrophy (DM) was studied by Western blot analysis, immunohistochemistry, and immunoelectron microscopy of DMPK. Western blot analysis showed that DMPK protein in DM skeletal muscles dramatically decreased. DMPK-positive muscle fibers showed typical DM pathological changes such as type I atrophy, central nuclei, nuclear chains, and sarcoplasmic masses. In degenerated DMPK-positive muscle fibers, cross-striated bands disappeared, and irregular granular DMPK-positive materials appeared in sarcoplasm. By immunoelectron microscopy, DMPK was localized in the terminal cisternae of the sarcoplasmic reticulum (SR) in DM muscle. Swollen DMPK-positive SRs were detected between well preserved myofibrils in the early stage of DM muscle degeneration, and degenerated intramembranous structures with DMPK and an accumulation of mitochondria were observed between disorganized myofibrils in degenerated DM muscle. We concluded that SR is the primary site of the degeneration of DM skeletal muscle and that the decreased DMPK might cause dysregulation of intracellular calcium metabolism, which is followed by DM muscle degeneration.

Adenosine Triphosphatases↗
PubMed2003

Relationship between cardiac protein tyrosine phosphorylation and myofibrillogenesis during axolotl heart development.

The axolotl, Ambystoma mexicanum, is a useful system for studying embryogenesis and cardiogenesis. To understand the role of protein tyrosine phosphorylation during heart development in normal and cardiac mutant axolotl embryonic hearts, we have investigated the state of protein tyrosine residues (phosphotyrosine, P-Tyr) and the relationship between P-Tyr and the development of organized sarcomeric myofibrils by using confocal microscopy, two-dimensional isoelectric focusing (IEF)/SDS-polyacrylamide gel electrophoresis (PAGE) and immunoblotting analyses. Western blot analyses of normal embryonic hearts indicate that several proteins were significantly tyrosine phosphorylated after the initial heartbeat stage (stage 35). Mutant hearts at stages 40-41 showed less tyrosine phosphorylated staining as compared to the normal group. Two-dimensional gel electrophoresis revealed that most of the proteins from mutant hearts had a lower content of phosphorylated amino acids. Confocal microscopy of stage 35 normal hearts using phosphotyrosine monoclonal antibodies demonstrated that P-Tyr staining gradually increased being localized primarily at cell-cell boundaries and cell-extracellular matrix boundaries. In contrast, mutant embryonic hearts showed a marked decrease in the level of P-Tyr staining, especially at sites of cell-cell and cell-matrix junctions. We also delivered an anti-phosphotyrosine antibody (PY 20) into normal hearts by using a liposome-mediated delivery method, which resulted in a disruption of the existing cardiac myofibrils and reduced heartbeat rates. Our results suggest that protein tyrosine phosphorylation is critical during myofibrillogenesis and embryonic heart development in axolotls.

Ambystoma mexicanum↗
PubMed1996

Morphological and immunohistochemical properties of primary long-term cultures of adult guinea-pig ventricular cardiomyocytes with peripheral cardiac neurons.

Long-term (2-12 weeks) cultures of adult guinea-pig ventricular myocytes, cocultured with neurons derived from stellate or intrinsic cardiac ganglia, retain their functional properties (Horackova et al., 1993, 1994, 1995). The present study was designed to investigate the morphological and immunochemical properties of such neurons and their associated cardiomyocytes. Cultured myocytes studied by means of phalloidin-rhodamine (for F-actin) and an antibody raised against myomes revealed parallel myofibrils with striations typical of rod-shaped cardiomyocytes, even while myocytes changed from cylindrical to flattened form as they established intercellular contacts. Microtubular networks, identified by alpha-tubulin DM1A antibody, were arrayed longitudinally in myofibrils, being especially prominent during the formation of intercellular contacts between myocytes. Histochemically identified adult peripheral autonomic neurons cultured alone or with myocytes displayed a variety of shapes. alpha-Tubulin staining was associated with the somata and neurites of various-shaped neurons whether cultured alone or with myocytes. Cultured neurons derived from stellate and intrinsic cardiac ganglia also exhibited staining for the general neuronal marker PGP 9.5 (protein gene product 9.5), and for specific markers of the following neurochemicals: tyrosine hydroxylase, acetylcholinesterase, choline acetyltransferase, neuropeptide Y, vasoactive intestinal peptide, calcitonin gene-related peptide, bradykinin, oxytocin, and NADPH-diaphorase. These data indicate that: (a) adult ventricular myocytes cocultured with intrathoracic neurons retain the structural properties of adult myocytes found in vivo; (b) intrinsic cardiac and extrinsic intrathoracic neurons cultured alone or with cardiomyocytes display morphological characteristics similar to those of neurons studied in situ; (c) intrinsic cardiac and intrathoracic extracardiac neurons cultured alone or with cardiomyocytes display a variety of morphologies (unipolar, bipolar, and multipolar), larger and more multipolar neurons being present in cultures derived from stellate versus intrinsic cardiac ganglia; (d) such cultured neurons are associated with a number of neurochemicals, more than one chemical being associated with each neuron. This model presents an excellent opportunity to study the morphology of individual peripheral extracardiac and intracardiac neurons as well as their potential to produce various neurochemicals that are known to be involved in the neuromodulation of cardiomyocyte function.

Animals↗
PubMed1997

Melittin and phospholipase A2 from bee (Apis mellifera) venom cause necrosis of murine skeletal muscle in vivo.

Melittin and phospholipase A2 (PLA2) from bee (Apis mellifera) venom were rested for their ability to induce necrosis of skeletal muscle cells after intramuscular injection into mice. Light and electron microscopic examination of tissue indicated that both melittin (4 micrograms/g) and bee venom PLA2 (4 micrograms/g) caused necrosis of skeletal muscle cells within 30 min after i.m. injection. Early changes in the cells consisted of delta lesions, indicating a ruptured plasma membrane, and hypercontraction of myofibrils. By 24 hr the affected cells appeared as an amorphous mass of disorganized and disrupted myofibrils contained in an intact basal lamina. To ensure that the myotoxic activity of the melittin preparation was not due to contaminating. PLA2 activity, the preparation was treated with p-bromophenacyl bromide (p-BPB), a known inhibitor of PLA2 activity. The p-BPB-treated melittin was determined to have no detectable PLA2 activity using a sensitive muscle cell culture assay, and it still induced myonecrosis, although to a lesser extent and of a slower onset. Additionally, p-BPB treatment of purified bee venom PLA2 completely inhibited its myotoxic activity. These results indicate that both melittin and bee venom PLA2 are capable of inducing necrosis of skeletal muscle cells upon i.m. injection, and that the catalytic and myotoxic activities of bee venom PLA2 are inihibited by p-BPB. Also, melittin and contaminating PLA2 in the melittin fraction may be acting synergistically to induce a stronger and more rapid myotoxic effect than occurs with either alone.

Acetophenones↗