BAM  9(2), 1999

                    47        The relation between skeletal muscle myopathy and exercise capacity in chronic heart failure
                                G Vescovo and L Dalla Libera     [Full text pdf 777Kb]

                    53        Differential inotropic effects of 4-aminopyridine and tetraethylammonium on rat diaphragm and limb muscles
                                E van Lunteren     [Full text pdf 194Kb]

                    61        Microvasculature of the unconditioned Latissimus Dorsi muscle after vascular delay and postmobilization
                                for cardiomyoplasty
                                R Scelsi, P Poggi and L Scelsi     [Full text pdf 394Kb]

                    65        Structural alterations of skeletal muscle induced by chronic administration of D-amphetamine and food restriction
                                JA Duarte, F Carvalho, K Natsis, F Remião, ML Bastos, JMC Soares and HJ Appell     [Full text pdf 436Kb]

                    71        Purification of myosin heavy chain isoforms by electroendosmotic preparative gel electrophoresis: characterization
                                of embryonic slow myosin heavy chain
                                M Sandri, C Rizzi, K Rossini, C Catani, M Cantini and M Spina   [Full text pdf 543Kb]  

                    79        Single and paired motor unit performance in skeletal muscles: comparison between simple and series-fibred muscles 
                                from the rat and the Guinea pig
                                PW Sheard, P McHannigan and MJ Duxson      [Full text pdf 62.5Kb]
 
 

The Relation between Skeletal Muscle Myopathy and Exercise Capacity in Chronic Heart Failure

Giorgio Vescovo and Luciano Dalla Libera⁽¹⁾

Divisione Medica I, Ospedale Civile di Venezia and (1) C.N.R. Unit for Muscle Physiopathology, Università di Padova
 

Chronic Heart Failure (CHF) is characterised by a leg skeletal muscle disorder with atrophy and shift from the "slow" aerobic fatigue resistant MHC1 to the "fast" more fatigable MHC2a and MHC2b. Atrophy has been shown to be, at least in non-cachectic patients, related more to TNFa -triggered myocyte apoptosis, rather than ubiquitin-dependent muscle waste. The CHF myopathy is specific and not secondary to detraining or atrophy. In fact the shift in MHCs is independent from muscle bulk loss since it appears before myocyte apoptosis and atrophy develop. It is due to adaptation to the relative ischemia of muscle fibres that is secondary to the capillary network damage. Moreover myofibres apoptosis is not selective. The shift in MHCs is, at least in part, responsible for the reduced exercise capacity in CHF patients. In fact there is a strong correlation between indices of severity of CHF, such as NYHA class, diuretic consumption and exercise time, and gastrocnemius MHC composition. The strongest correlation is however with cardiopulmonary exercise testing parameters (peak VO₂, VT and O₂ pulse) that are the most objective measurements of exercise capacity.

Muscle fatigue which limits exercise capacity, appears earlier in patients that have a greater skeletal muscle expression of MHC2a and MHC2b. These isoforms have in fact higher speed of shortening, ATP consumption, and lower threshold for lactate production, so that they reach anaerobic metabolism and symptoms of muscle fatigue much earlier.

Key words: chronic heart failure, skeletal muscle, myosin heavy chains, exercise capacity.

Dr. Giorgio Vescovo, Divisione Medica I, Ospedale Civile di Venezia, 30100 Venezia, Italy, phone +39 041 5294361, fax +39 041 5294651.

Differential Inotropic Effects of 4-Aminopyridine and Tetraethylammonium on Rat Diaphragm and Limb Muscles

Erik van Lunteren

Departments of Medicine and Neurosciences, Case Western Reserve University and Cleveland VA Medical Center, Cleveland, USA

K⁺ channels regulate action potential duration and thereby force of skeletal muscles. Diaphragm differs from limb muscles in the dependence of contraction on extracellular Ca⁺⁺. We hypothesized that diaphragm also differs from limb muscles in the regulation of contraction by membranous K⁺ conductances. This was tested in vitro by assessing changes in isometric twitch force and kinetics in response to K⁺ channel blockers, and comparing responses of rat diaphragm with that of two limb muscles, the extensor digitorum longus (which contains mainly fast-twitch fibers) and the soleus (which contains mainly slow-twitch fibers). 4-Aminopyridine (0.3 mM) increased twitch force of diaphragm by 71 ± 7%, which was significantly more than that of the extensor digitorum longus (28 ± 11%, P < 0.005) and the soleus (22 ± 3%, P < 0.005). In contrast, tetraethylammonium (10 mM) increased twitch force of the diaphragm by 9 ± 1%, which furthermore was smaller than that of the extensor digitorum longus (41 ± 2%, P < 0.001) and soleus (53 ± 3%, P < 0.001) muscles. There was also a differential pattern among muscles in percent prolongation of isometric contraction time, which paralleled that of twitch force augmentation. Charybdotoxin (10 nM), apamin (100 nM) and glibenclamide (100 mM) did not alter muscle isometric twitch force or kinetics of any muscle. Thus the pattern of diaphragm muscle responses to the K⁺ channel blockers 4-aminopyridine and tetraethylammonium differs from that of limb muscles. This can not be attributed to differential blockade among muscles of ATP-sensitive or Ca⁺⁺-activated K⁺ channels, but could be explained if diaphragm contains different delayed rectifier K⁺ channel subtypes from those found in limb muscle.

Key words: diaphragm, limb muscle, rat, contraction, 4-aminopyridine, tetraethylammonium.

Microvasculature of the Unconditioned Latissimus Dorsi Muscle after Vascular Delay and Postmobilization for Cardiomyoplasty

Roberto Scelsi, Paola Poggi⁽¹⁾ and Laura Scelsi⁽²⁾

Department of Human Pathology, University of Pavia, (1) Institute of Human Normal Anatomy, University of Pavia and (2) Department of Cardiology, IRCCS Policlinico S. Matteo, Pavia, Italy

Vascular deafferentation of the Latissimus Dorsi Muscle (LDM) for dynamic cardiomyoplasty is an important cause of ischemia in the distal portion of the muscle with degeneration of muscle fibres and consequent reduction in the effectiveness of the surgery.

Experimental studies suggest that a vascular delay procedure and a 10-day delay adaptation significantly improve the distal perfusion and function of the LDM flap for cardiomyoplasty.

We here report a comparative histological and ultrastructural study of biopsies from unconditioned LDM flaps of two patients, taken 30 days after vascular deafferentation and dynamic cardiomyoplasty, and 10 days after a vascular delay procedure, respectively.

In the first case, in the distal part of LDM we found muscle atrophy and degeneration, necrosis of capillaries, with swelling of endothelial cells and disruption of cytoplasmic organelles, and capillary neoangiogenesis. In the second patient, the distal LDM after vascular delay procedure show minimal muscle fibre degeneration, dilatation of capillaries with endothelial cell preservation, and scarce capillary neoangiogenesis.

The present results seem to confirm that a vascular delay procedure on LDM for use with cardiomyoplasty may improve the LDM perfusion and function, inducing moderate morphological changes in muscle fibres and vasculature in comparison to the deafferentated LDM.

Key words: vascular delay, dynamic cardiomyoplasty, Latissimus Dorsi flap, damage.

Prof. Roberto Scelsi, Department of Human Pathology, University of Pavia, Italy, phone +39 0382 528474, fax +39 0382 525866, Email

Structural Alterations of Skeletal Muscle Induced by Chronic Administration of D-Amphetamine and Food Restriction

José A. Duarte⁽¹⁾, Felix Carvalho⁽²⁾, Konstantinos Natsis⁽³⁾, Fernando Remião⁽²⁾, Maria L. Bastos⁽²⁾, José M.C. Soares⁽¹⁾ and Hans J. Appell^{(1, 4)}

(1) Department of Sports Biology, Faculty of Sport Sciences, University of Porto, Portugal, (2) Department of Toxicology, Faculty of Pharmacy, University of Porto, Portugal, (3) Department of Anatomy, Faculty of Medicine, Aristotelian University of Thessaloniki, Greece and (4) Institute of Sport Orthopedics, German Sport University Cologne, Germany

Amphetamines are frequently used as anorexigenic drugs to facilitate fasting and weight loss, although some side effects are known. The objective of the study was to study the effects of fasting induced by amphetamine administration as compared to food restriction alone on skeletal muscle. Twelve male Wistar rats were assigned to three groups: One group (AMPH) received d-amphetamine sulphate during 14 days (20 mg/Kg/day, s.c.); group FRES was the pair-fed, food restricted control receiving each day the same quantity of food consumed by the AMPH group the day before; a control group (CONT) was fed ad libitum. Food intake and body weights were controlled daily. After 14 days the animals were sacrificed and the soleus muscles were removed for light and electron microscopical evaluation and muscle fiber morphometry. Towards the end of the experimental period, food intake returned to normal in the AMPH group due to amphetamine tolerance. The AMPH and FRES animals experienced a comparable weight loss of about 15%. The muscles fibers of the AMPH and FRES group showed a slightly (n.s.) higher incidence of central nuclei than the CONT group. Their muscle fibers atrophied by about 25%. Signs of degeneration and regeneration were observed at the ultrastructural level in both experimental groups. It is concluded that the deleterious effects on skeletal muscle are rather the common result of the alimentary restriction than the particular effect of amphetamine.

Key words: amphetamine, food-restriction, skeletal muscle damage, muscle atrophy, rats.

Prof. Dr. Hans-Joachim Appell, Institute of Sport Orthopedics, German Sport University, D-50927 Cologne, Germany, phone +49 221 4982543, fax +49 221 4912001, Email appell@hrz.dshs-koeln.de.

Purification of Myosin Heavy Chain Isoforms by Electroendosmotic Preparative Gel Electrophoresis: Characterization of Embryonic Slow Myosin Heavy Chain

Marco Sandri^{(1, 2)}, Corrado Rizzi⁽¹⁾, Katia Rossini⁽¹⁾, Claudia Catani⁽¹⁾, Marcello Cantini⁽¹⁾ and Michele Spina⁽³⁾

(1) C.N.R. Unit for Muscle Biology and Physiopathology, Department of Biomedical Sciences, (2) Institute of Experimental and Laboratory Medicine and (3) Institute of Histology and General Embryology, University of Padova, Padova, Italy

Myosin is a hexapolypeptide constituted by four light and two heavy chains the isoforms of which segregate differently in specific stages of animal development and in different fiber types in adulthood. In mammals the Myosin Heavy Chains (MHC) are polypeptides with a molecular mass of about 200 KDa which isoforms can be identified by SDS PAGE and/or immunochemistry. A method for the purification of myosin heavy chain isoforms using a SDS Electrendosmotic Preparative Gel Electrophoresis (SDS EPGE) is described. Semplicity and reproducibility of this approach permits purification of single isoforms from complex mixture with a sufficient high recovery to perform immunochemical or biochemical studies. The possibility to apply useful tool as SDS removal and protein concentration by KDS precipitation before further analysis on the sample is described. Application of the methodology to the study of slow type embryonic MHC by enzymatic as well as chemical peptide mapping and amino acid composition is described.

Key words: EPGE, KDS-precipitation, MHC isoforms, peptide mapping, amino acid analysis, muscle.

Dr. Marco Sandri, M.D., Department of Biomedical Sciences, University of Padova, Italy, phone +39 049 8276030, fax +39 8276040, Email patgen06@civ.bio.unipd.it.

Single and Paired Motor Unit Performance in Skeletal Muscles: Comparison Between Simple and Series-Fibred Muscles from the Rat and the Guinea Pig

Philip W. Sheard, Peter McHannigan and Marilyn J. Duxson⁽¹⁾

Developmental Biology Unit, Department of Physiology and (1) Developmental Biology Unit, Department of Anatomy & Structural Biology, University of Otago, Dunedin, New Zealand

We have compared the performance of isolated motor units in a simple parallel fibred rat skeletal muscle with those of a parallel series-fibred guinea pig skeletal muscle. In the rat muscle tension may be delivered efficiently to the tendons since all fibres have tendonous insertions at both ends, while in the guinea pig muscle most fibres terminate intrafascicularly so the pathway for tension delivery includes neighbouring fibres thereby introducing a series compliance. The properties of tension delivery through series fibres is likely to vary as a function of their stiffness (i.e. whether or not they are coactive) and therefore might be altered by motor unit usage patterns. To test this hypothesis we measured the physiological properties of pairs of isolated motor units when stimulated individually and when stimulated together. We found that coactivation of pairs of motor units on average resulted in delivery of more than the sum of the tension of the two contributing units, and that this was greater for the guinea pig than for the rat muscle (19.8% vs. 8.7% increase). The results indicate that tension delivery is modulated by interaction between active and inactive fibres, and that the spatial arrangement of active fibres across and along the muscle belly is a critical determinant of performance in the case of the series-fibred muscle.

Key words: skeletal muscle, motor unit, tension delivery, fibre architecture.

Dr. P.W. Sheard, phone (64 3) 479 7464, fax (64 3) 479 7323, Email phil.sheard@stonebow.otago.ac.nz.