Adverse effects of myasthenia gravis on rat phrenic diaphragm contractile performance

2004 ◽  
Vol 97 (3) ◽  
pp. 895-901 ◽  
Author(s):  
Erik van Lunteren ◽  
Michelle Moyer ◽  
Henry J. Kaminski
Keyword(s):  
Myasthenia Gravis ◽  
Muscle Function ◽  
Initial Period ◽  
Neuromuscular Diseases ◽  
Diaphragm Muscle ◽  
Twitch Force ◽  
Continuous Stimulation ◽  
Intermittent Stimulation ◽  
Contractile Performance

Myasthenia gravis has variable effects on the respiratory system, ranging from no abnormalities to life-threatening respiratory failure. Studies characterized diaphragm muscle contractile performance in rat autoimmune myasthenia gravis. Rats received monoclonal antibody that recognizes acetylcholine receptor determinants (or inactive antibody); 3 days later, phrenic nerve and diaphragm were studied in vitro. Myasthenic rats segregated into two groups, those with normal vs. impaired limb muscle function when tested in intact animals (“mild” and “severe” myasthenic). Baseline diaphragm twitch force was reduced for both severe ( P < 0.01) and mild ( P < 0.05) myasthenic compared with control animals (twitch force: normal 1,352 ± 140, mild myasthenic 672 ± 99, severe myasthenic 687 ± 74 g/cm2). However, only severe myasthenic diaphragm had impaired diaphragm endurance, based on significantly ( P < 0.05) accelerated rate of peak force decline during the initial period of stimulation (0.02 + 0.02, 0.03 ± 0.01, and 0.09 ± 0.01%/pulse for normal, mild myasthenic, and severe myasthenic, respectively, during continuous stimulation) and intratrain fatigue (up to 30.5 ± 7.4% intratrain force drop in severe myasthenic vs. none in normal and mild myasthenic, P < 0.01). Furthermore, compared with continuous stimulation, intermittent stimulation had a protective effect on force of severe myasthenic diaphragm (force after 2,000 pulses was 31.4 ± 2.0% of initial during intermittent stimulation vs. 13.0 ± 2.1% of initial during continuous stimulation, P < 0.01) but not on normal diaphragm. These data indicate that baseline force and fatigue may be affected to different extents by varying severity of myasthenia gravis and furthermore provide a mechanism by which alterations in breathing pattern may worsen respiratory muscle function in neuromuscular diseases.

Effect of Phasic Activation on Endplate Potential in Rat Diaphragm

1999 ◽  
Vol 82 (6) ◽  
pp. 3030-3040 ◽  
Author(s):  
Michelle Moyer ◽  
Erik van Lunteren
Keyword(s):  
Time Course ◽  
Complete Recovery ◽  
Stimulation Frequency ◽  
Drop Out ◽  
Rat Diaphragm ◽  
Continuous Stimulation ◽  
Intermittent Stimulation ◽  
Rate Of Decline ◽  
Phasic Activation

Neuromuscular junction endplate potentials (EPPs) decrease quickly and to a large extent during continuous stimulation. The present study examined the hypothesis that EPP rundown recovers rapidly, thereby substantially preserving neurotransmission during intermittent compared with continuous stimulation. Studies were performed in vitro on rat diaphragm, using μ-conotoxin to allow recording of normal-sized EPPs from intact fibers. During continuous 5- to 100-Hz stimulation, EPP amplitude declined with a biphasic time course. The initial fast rate of decline was modulated substantially by stimulation frequency, whereas the subsequent slow rate of decline was relatively frequency independent. During intermittent 5- to 100-Hz stimulation (duty cycle 0.33), EPP amplitude declined rapidly during each train, but recovered substantially by the onset of the following train. The intra-train declines were substantially greater than the inter-train declines in EPP amplitude. Intra-train reductions in EPP amplitude were stimulation frequency dependent, based on both the total decline and rate constant of EPP decline. In contrast, the degree of recovery from train to train was independent of stimulation frequency, indicating low frequency dependence of inter-train rundown. The substantial recovery of EPP amplitude in between trains resulted in greater cumulative EPP size during intermittent compared with continuous stimulation. During continuous stimulation, EPP drop-out was only seen during 100-Hz stimulation; this was completed mitigated during intermittent stimulation. Miniature EPP size was unaffected by either continuous or intermittent stimulation. The pattern of rapid intra-train rundown and slow inter-train rundown of EPP size during intermittent stimulation is therefore due to rapid changes in the magnitude of neurotransmitter release rather than to axonal block or postsynaptic receptor desensitization. These findings indicate considerable rundown of EPP amplitudes within a stimulus train, with near complete recovery by the onset of the next train. This substantially attenuates the decrement in EPP amplitude during intermittent compared with continuous stimulation, thereby preserving the integrity of neurotransmission during phasic activation.

scholarly journals Sphingomyelinase stimulates oxidant signaling to weaken skeletal muscle and promote fatigue

2010 ◽  
Vol 299 (3) ◽  
pp. C552-C560 ◽  
Author(s):  
Leonardo F. Ferreira ◽  
Jennifer S. Moylan ◽  
Laura A. A. Gilliam ◽  
Jeffrey D. Smith ◽  
Mariana Nikolova-Karakashian ◽  
...  
Keyword(s):  
Muscle Function ◽  
Muscle Force ◽  
Fold Increase ◽  
Diaphragm Muscle ◽  
Fiber Bundles ◽  
C2c12 Myotubes ◽  
Specific Force ◽  
Nonmuscle Cells ◽  
Failure Conditions

Sphingomyelinase (SMase) hydrolyzes membrane sphingomyelin into ceramide, which increases oxidants in nonmuscle cells. Serum SMase activity is elevated in sepsis and heart failure, conditions where muscle oxidants are increased, maximal muscle force is diminished, and fatigue is accelerated. We tested the hypotheses that exogenous SMase and accumulation of ceramide in muscle increases oxidants in muscle cells, depresses specific force of unfatigued muscle, and accelerates the fatigue process. We also anticipated that the antioxidant N-acetylcysteine (NAC) would prevent SMase effects on muscle function. We studied the responses of C2C12 myotubes and mouse diaphragm to SMase treatment in vitro. We observed that SMase caused a 2.8-fold increase in total ceramide levels in myotubes. Exogenous ceramide and SMase elevated oxidant activity in C2C12 myotubes by 15–35% ( P < 0.05) and in diaphragm muscle fiber bundles by 58–120% ( P < 0.05). The SMase-induced increase in diaphragm oxidant activity was prevented by NAC. Exogenous ceramide depressed diaphragm force by 55% ( P < 0.05), while SMase depressed maximal force by 30% ( P < 0.05) and accelerated fatigue—effects opposed by treatment with NAC. In conclusion, our findings suggest that SMase stimulates a ceramide-oxidant signaling pathway that results in muscle weakness and fatigue.

ATP-sensitive K+ channel blocker glibenclamide and diaphragm fatigue during normoxia and hypoxia

1998 ◽  
Vol 85 (2) ◽  
pp. 601-608 ◽  
Author(s):  
Erik Van Lunteren ◽  
Michelle Moyer ◽  
Augusto Torres
Keyword(s):  
Relaxation Time ◽  
Diaphragm Muscle ◽  
K Channel ◽  
Adult Rat ◽  
Fatigue Development ◽  
Stimulation Paradigm ◽  
Contractile Performance ◽  
Modest Effect

The role of ATP-sensitive K+ channels in skeletal muscle contractile performance is controversial: blockers of these channels have been found to not alter, accelerate, or attenuate fatigue. The present study reexamined whether glibenclamide affects contractile performance during repetitive contraction. Experiments systematically assessed the effects of stimulation paradigm, temperature, and presence of hypoxia and in addition compared intertrain with intratrain fatigue. Adult rat diaphragm muscle strips were studied in vitro. At 37°C and normoxia, glibenclamide did not significantly affect any measure of fatigue during continuous 5- or 100-Hz or intermittent 20-Hz stimulation but progressively prolonged relaxation time during 20-Hz stimulation. At 20°C and normoxia, neither force nor relaxation rate was affected significantly by glibenclamide during 20-Hz stimulation. At 37°C and hypoxia, glibenclamide did not significantly affect fatigue at 5-Hz or intertrain fatigue during 20-Hz stimulation but reduced intratrain fatigue and prolonged relaxation time during 20-Hz stimulation. These findings indicate that, although ATP-sensitive K+ channels may be activated during repetitive contraction, their activation has only a modest effect on the rate of fatigue development.

β2-Adrenoceptor agonists reduce the decline of rat diaphragm twitch force during severe hypoxia

1999 ◽  
Vol 276 (3) ◽  
pp. L474-L480 ◽  
Author(s):  
H. F. M. van der Heijden ◽  
L. M. A. Heunks ◽  
H. Folgering ◽  
C. L. A. van Herwaarden ◽  
P. N. R. Dekhuijzen
Keyword(s):  
Diaphragm Muscle ◽  
Severe Hypoxia ◽  
Rat Diaphragm ◽  
Duration Of Action ◽  
Inotropic Effects ◽  
Twitch Force ◽  
Control Value ◽  
Adrenoceptor Agonist ◽  
Long Acting

The aim of the present study was to investigate the in vitro effects of the short-acting β2-adrenoceptor agonist salbutamol and the long-acting β2-adrenoceptor agonist salmeterol on hypoxia-induced rat diaphragm force reduction. In vitro diaphragm twitch force (Pt) and maximal tetanic force (Po) of isolated diaphragm muscle strips were measured for 90 min during hyperoxia (tissue bath [Formula: see text] 83.8 ± 0.9 kPa and [Formula: see text] 3.9 ± 0.1 kPa) or severe hypoxia ([Formula: see text] 7.1 ± 0.3 kPa and [Formula: see text] 3.9 ± 0.1 kPa) in the presence and absence of 1 μM salbutamol or 1 μM salmeterol. During hyperoxia, salbutamol and salmeterol did not significantly alter the time-related decreases in Pt and Po (to ∼50% of initial values). Salbutamol had no effects on Po or the Pt-to-Poratio. Salmeterol treatment significantly reduced Po and increased the Pt-to-Poratio during hyperoxia ( P < 0.05 compared with control value). Hypoxia resulted in a severe decrease in Pt (to ∼30% of initial value) and Po after 90 min. Both salbutamol and salmeterol significantly reduced the decline in Pt during hypoxia ( P < 0.05). The reduction in Po was not prevented. Salbutamol increased Pt rapidly but transiently. Salmeterol had a delayed onset of effect and a longer duration of action. Addition of 1 μM propranolol (a nonselective β-adrenoceptor antagonist) did not alter Pt, Po, or the Pt-to-Poratio during hypoxia but completely blocked the inotropic effects of salbutamol and salmeterol, indicating that these effects are dependent on β2-adrenoceptor agonist-related processes.

scholarly journals Creatine Supplementation for Patients with Inflammatory Bowl Diseases: A Scientific Rationale for a Clinical Trial

Nutrients ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 1429
Author(s):  
Theo Wallimann ◽  
Caroline H. T. Hall ◽  
Sean P. Colgan ◽  
Louise E. Glover
Keyword(s):  
Ulcerative Colitis ◽  
Clinical Trial ◽  
Crohn’S Disease ◽  
Pilot Study ◽  
Crohn's Disease ◽  
Single Case ◽  
Initial Period ◽  
Creatine Supplementation

Based on theoretical considerations, experimental data with cells in vitro, animal studies in vivo, as well as a single case pilot study with one colitis patient, a consolidated hypothesis can be put forward, stating that “oral supplementation with creatine monohydrate (Cr), a pleiotropic cellular energy precursor, is likely to be effective in inducing a favorable response and/or remission in patients with inflammatory bowel diseases (IBD), like ulcerative colitis and/or Crohn’s disease”. A current pilot clinical trial that incorporates the use of oral Cr at a dose of 2 × 7 g per day, over an initial period of 2 months in conjunction with ongoing therapies (NCT02463305) will be informative for the proposed larger, more long-term Cr supplementation study of 2 × 3–5 g of Cr per day for a time of 3–6 months. This strategy should be insightful to the potential for Cr in reducing or alleviating the symptoms of IBD. Supplementation with chemically pure Cr, a natural nutritional supplement, is well tolerated not only by healthy subjects, but also by patients with diverse neuromuscular diseases. If the outcome of such a clinical pilot study with Cr as monotherapy or in conjunction with metformin were positive, oral Cr supplementation could then be used in the future as potentially useful adjuvant therapeutic intervention for patients with IBD, preferably together with standard medication used for treating patients with chronic ulcerative colitis and/or Crohn’s disease.

scholarly journals The Influence of a Knitted Hydrophilic Prosthesis of Blood Vessels on the Activation of Coagulation System—In Vitro Study

Nanomaterials ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 1600
Author(s):  
Maria Szymonowicz ◽  
Maciej Dobrzynski ◽  
Sara Targonska ◽  
Agnieszka Rusak ◽  
Zbigniew Rybak ◽  
...  
Keyword(s):  
Blood Vessels ◽  
Initial Period ◽  
In Vitro Study ◽  
Vascular Prosthesis ◽  
Coagulation System ◽  
Factor Xii ◽  
Scanning Calorimetry ◽  
Vascular Prostheses ◽  
Control Value

The replacement of affected blood vessels of the polymer material can cause imbalances in the blood haemostatic system. Changes in blood after the implantation of vascular grafts depend not only on the chemical composition but also on the degree of surface wettability. The Dallon® H unsealed hydrophilic knitted vascular prosthesis double velour was assessed at work and compare with hydrophobic vascular prosthesis Dallon®. Spectrophotometric studies were performed in the infrared and differential scanning calorimetry, which confirmed the effectiveness of the process of modifying vascular prostheses. Determination of the parameters of coagulation time of blood after contact in vitro with Dallon® H vascular prosthesis was also carried out. Prolongation of activated thromboplastin time, decreased activity of factor XII, IX and VIII, were observed. The prolonged thrombin and fibrinogen were reduced in the initial period of the experiment. The activity of plasminogen and antithrombin III and protein C were at the level of control value. The observed changes in the values of determined parameters blood coagulation do not exceed the range of referential values for those indexes. The observed changes are the result of considerable blood absorptiveness by the prosthesis of blood vessels and their sealing.

scholarly journals DNA Unwinding Is an MCM Complex-dependent and ATP Hydrolysis-dependent Process

2004 ◽  
Vol 279 (44) ◽  
pp. 45586-45593 ◽  
Author(s):  
David Shechter ◽  
Carol Y. Ying ◽  
Jean Gautier
Keyword(s):  
Dna Replication ◽  
Neutralizing Antibodies ◽  
Atp Hydrolysis ◽  
Initial Period ◽  
Dna Helicase ◽  
Dna Unwinding ◽  
Origin Firing ◽  
Replicative Helicase ◽  
Mcm Proteins

Minichromosome maintenance proteins (Mcm) are essential in all eukaryotes and are absolutely required for initiation of DNA replication. The eukaryotic and archaeal Mcm proteins have conserved helicase motifs and exhibit DNA helicase and ATP hydrolysis activitiesin vitro. Although the Mcm proteins have been proposed to be the replicative helicase, the enzyme that melts the DNA helix at the replication fork, their function during cellular DNA replication elongation is still unclear. Using nucleoplasmic extract (NPE) fromXenopus laeviseggs and six purified polyclonal antibodies generated against each of theXenopusMcm proteins, we have demonstrated that Mcm proteins are required during DNA replication and DNA unwinding after initiation of replication. Quantitative depletion of Mcms from the NPE results in normal replication and unwinding, confirming that Mcms are required before pre-replicative complex assembly and dispensable thereafter. Replication and unwinding are inhibited when pooled neutralizing antibodies against the six different Mcm2–7 proteins are added during NPE incubation. Furthermore, replication is blocked by the addition of the Mcm antibodies after an initial period of replication in the NPE, visualized by a pulse of radiolabeled nucleotide at the same time as antibody addition. Addition of the cyclin-dependent kinase 2 inhibitor p21cip1specifically blocks origin firing but does not prevent helicase action. When p21cip1is added, followed by the non-hydrolyzable analog ATPγS to block helicase function, unwinding is inhibited, demonstrating that plasmid unwinding is specifically attributable to an ATP hydrolysis-dependent function. These data support the hypothesis that the Mcm protein complex functions as the replicative helicase.

Abstract P459: Mavacamten And Danicamtiv Reverse Respective Contractile Abnormalities In Engineered Heart Tissue Models Of Hypertrophic And Dilated Cardiomyopathy

2021 ◽  
Vol 129 (Suppl_1) ◽  
Author(s):  
Saiti S Halder ◽  
Lorenzo R Sewanan ◽  
Michael J Rynkiewicz ◽  
Jeffrey R Moore ◽  
William J Lehman ◽  
...  
Keyword(s):  
Dilated Cardiomyopathy ◽  
Calcium Sensitivity ◽  
Heart Tissue ◽  
Missense Mutations ◽  
Wild Type ◽  
Twitch Force ◽  
In Vitro Motility ◽  
Isometric Twitch ◽  
Engineered Heart Tissues

Missense mutations in alpha-tropomyosin (TPM1) can lead to development of hypertrophic (HCM) or dilated cardiomyopathy (DCM). HCM mutation E62Q and DCM mutation E54K have previously been studied extensively in experimental systems ranging from in vitro biochemical assays to animal models, although some conflicting results have been found. We undertook a detailed multi-scale assessment of these mutants that included atomistic simulations, regulated in vitro motility (IVM) assays, and finally physiologically relevant human engineered heart tissues. In IVM assays, E62Q previously has shown increased Calcium sensitivity. New molecular dynamics data shows mutation-induced changes to tropomyosin dynamics and interactions with actin and troponin. Human engineered heart tissues (EHT) were generated by seeding iPSC-derived cardiomyocytes engineered using CRISPR/CAS9 to express either E62Q or E54K cardiomyopathy mutations. After two weeks in culture, E62Q EHTs showed a drastically hypercontractile twitch force and significantly increased stiffness while displaying little difference in twitch kinetics compared to wild-type isogenic control EHTs. On the other hand, E54K EHTs displayed hypocontractile isometric twitch force with faster kinetics, impaired length-dependent activation and lowered stiffness. Given these contractile abnormalities, we hypothesized that small molecule myosin modulators to appropriately activate or inhibit myosin activity would restore E54K or E62Q EHTs to normal behavior. Accordingly, E62Q EHTs were treated with 0.5μM mavacamten (to remedy hypercontractility) and E54K EHTs with 0.5 μM danicamtiv (to remedy hypocontractility) for 4 days, followed by a 1 day washout period. Upon contractility testing, it was observed that the drugs were able to reverse contractile phenotypes observed in mutant EHTs and restore contractile properties to levels resembling those of the untreated wild type group. The computational, IVM and EHT studies provide clear evidence in support of the hyper- vs. hypo-contractility paradigm as a common axis that distinguishes HCM and DCM TPM1 mutations. Myosin modulators that directly compensate for underlying myofilament aberrations show promising efficacy in human in vitro systems.

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