Biomedical Physiology and Kinesiology - Theses, Dissertations, and other Required Graduate Degree Essays

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Proton modulation of the cardiac voltage-gated sodium channel

Author: 
Date created: 
2012-09-17
Abstract: 

Voltage-gated sodium (NaV) channels generate the action potential upstroke in most electrically excitable cells. The cardiac-isoform, NaV1.5, is the predominant NaV channel in cardiac muscle. Changes in NaV1.5 channel function often lead to cardiac dysfunction resulting in syncope, cardiac arrhythmia, and even sudden cardiac death. Extracellular protons block NaV1.5 channel conductance with a pKa ≈ 6.0 and shift the voltage-dependence of NaV1.5 channel function to more positive potentials. During cardiac ischemia extracellular pH drops to as low as pH 6.0 within 10 minutes of its onset. A detailed analysis of the effects of protons on NaV1.5 channel function has not been completed. Further, the molecular underpinnings of the proton-channel interaction remain unknown. Characterizing NaV1.5 channel proton modulation will contribute to the treatment and prevention of the life-threatening events that occur during and following cardiac ischemia and acidosis. In this study wild-type and mutant NaV1.5 channels were expressed in Xenopus laevis oocytes. Ionic and gating NaV1.5 currents were recorded with extracellular solution titrated to pH 4.0 through pH 8.0 using a cut-open voltage clamp. These data demonstrate three critical findings: (1) extracellular protons destabilize the fast and slow-inactivated states of NaV1.5 channels, (2) destabilization of the fast-inactivated state occurs through proton modulation of NaV1.5 channel gating charge, (3) protons interact within the NaV1.5 channel pore to modulate the slow-inactivated state

Document type: 
Thesis
File(s): 
Supervisor(s): 
Peter C. Ruben
Tom W. Claydon
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Dissertation) Ph.D.

Investigating syncope in children and adolescents

Date created: 
2012-08-08
Abstract: 

Syncope, or fainting, is a heterogeneous condition and hence difficult to diagnose. Treatments for syncope are vast and largely ineffective because individual variability impacts success. Research into the mechanisms and treatment of syncope has focused on adults, despite 15-25% of children experiencing episodes. Thus, we aimed to investigate syncope in children and adolescents and explore a non-pharmacological approach to its treatment. We conducted cardiovascular autonomic function testing (Valsalva manoeuvre, cerebral reactivity to hypo- and hypercapnia, and orthostatic stress testing) to evaluate cardiovascular factors predisposing to syncope in 21 children. We also evaluated the efficacy of graded calf compression stockings for the treatment of syncope in 15 young adults. We found that (1) autonomic function testing in children was appropriate, but current diagnostic criteria may need to be altered for paediatric populations; and (2) the utility of calf compression stockings to improve orthostatic tolerance is dependent on specific anthropometric variables.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Victoria Claydon
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) M.Sc.

The distribution of the inositol phosphatase SHIP1 in a murine model of Amyotrophic Lateral Sclerosis (ALS)

Date created: 
2012-07-17
Abstract: 

Src homology 2 domain-containing inositol-5’ phosphatase (SHIP1) is a protein which suppresses the activation, proliferation, and survival of hematopoietic cells. Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by the degeneration of specific neuron populations which leads to atrophy of skeletal muscles, paralysis, and death. Microgliosis is a common hallmark in ALS patients and in mouse models having over-expression of SOD1 (mSOD1); however, the association between microgliosis and disease progression has not yet been determined. Using immunohistochemistry (IHC), SHIP1 expression in macrophages and microglia was investigated in the lumbar spinal cord of control and mSOD1 mice at 3 time points: 11 weeks (asymptomatic), 15 weeks (symptomatic), and 18 weeks (advanced stage). A significant increase in SHIP1 immunoreactivity was found between control mice and diseased mice at symptomatic and advanced stages. SHIP1 immunoreactivity also significantly increased throughout disease progression suggesting that SHIP1 is involved in regulating microgliosis in ALS.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Charles Krieger
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) M.Sc.

The effect of exercise on the cardio-postural relationship

Author: 
Date created: 
2012-05-11
Abstract: 

Syncope is common in individuals who experience orthostatic hypotension which is often associated with cardiovascular conditions, brain injuries, and ageing. A bi-directional link between the cardiovascular and postural control systems was recently identified, and may provide insight into syncope and orthostatic hypotension. This thesis examined the inter-dependent relationship between cardiovascular and postural controls before and after light exercise to induce mild orthostatic stress. It was hypothesized that after exercise, there would be a greater reliance on the skeletal muscle pump to prevent venous pooling to maintain cardiac output and blood pressure, and that this effect would be more pronounced in men. There was an increase in skeletal muscle pump activity which maintained venous return and increased posture stability. In addition, there was a shift in the overall interaction dynamics between the two systems with a greater dependence on posture control to maintain venous return after exercise, particularly in men.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Andrew Blaber
Victoria Claydon
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) M.Sc.

Loss of muscle performance in seniors: changes to the dynamic muscle structure and muscle gearing

Author: 
Date created: 
2012-04-18
Abstract: 

Muscle structure changes with ageing in a manner that can alter its contractile mechanics, resulting in a reduction in strength and mobility. Fascicles within a muscle can shorten at slower velocities than the muscle belly, in a process known as belly gearing. Belly gearing allows the fascicles to produce a greater force when they contract. However, it may be compromised when we age. The gastrocnemii muscles in the calf were imaged in young adults and seniors using ultrasound. Their muscle structures were compared during standing and during ankle extensions. The overall gearing of a muscle-tendon-unit was largely determined by the belly gearing, but its variability was driven by changes in tendon stretch. The decrease in performance and power output in seniors may be associated with reduced gearing due to atrophy of the muscles.

Document type: 
Thesis
File(s): 
Supervisor(s): 
James Wakeling
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) M.Sc.

3D muscle architecture in the triceps surae muscle: 3D ultrasound methods and maps of fascicle orientation and curvature

Author: 
Date created: 
2012-03-13
Abstract: 

Muscle fascicle architecture is an important parameter affecting the mechanical function of skeletal muscle. Most previous studies on fascicle architecture have been in 2D and the importance of 3rd dimension has not been much explored. The 3D orientation of the whole muscle may be regionalized in the muscle and can change with the contraction state of the muscle. Fascicles are arranged as sheets in muscles and the sheets’ arrangement may change when the muscle bulges during contraction. With the muscle bulging, fascicle sheets may deform and affect the 3D fascicle orientations which will further influence the force generated by the muscle. In this thesis methods were developed and validated to study the in-vivo muscle fascicle architecture in 3D using B-mode ultrasound and optical tracking systems. Images were obtained from multiple scans of the muscles with scan times less than two minutes and analyzed for fascicle orientations, fascicle curvatures, fascicle sheet orientations and fascicle sheet curvatures. The 3D architecture information further was used to study the effect of ultrasound probe orientation and position on the measured 2D fascicle orientations. The orientation and curvature values of the fascicles and the fascicle sheets were quantified in the soleus and the gastrocnemii muscles in six male subjects for three torque levels 0%, 30% and 60% of MVC and four ankle angles -15°, 0°, 15° and 30° of planter flexion. The probe orientation and position was more critical in soleus than the gastrocnemii muscle due to more complex fascicle arrangement. Fascicle orientations and curvature values were regionalized across the muscles and changed with the change in ankle angle and relative torque level, p<0.01. The change in fascicle arrangement may be in response to the intramuscular pressure, and these changes can alter the mechanical output. The 3D information obtained in this thesis will be useful to understand the force generation of muscle and also to understand the change in muscle function with diseases affecting the muscle architecture.

Document type: 
Thesis
File(s): 
Supervisor(s): 
James M. Wakeling
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Dissertation) Ph.D.

Cerebrovascular control following spinal cord injury

Date created: 
2011-12-02
Abstract: 

Spinal cord injury (SCI) leads to drastic loss of motor and sensory function. The autonomic consequences of SCI are less well known and include diminished cardiovascular control, with large decreases and increases in blood pressure; conditions known as orthostatic hypotension (OH) and autonomic dysreflexia (AD), respectively. These disorders have important quality of life implications for individuals with SCI, due not only to blood pressure fluctuations, but also due to proposed alterations in cerebral perfusion secondary to impaired cerebral autoregulation. However, comprehensive studies examining autoregulation during OH and AD after SCI are scarce. We, therefore, determined cardiovascular and cerebrovascular responses to these conditions in individuals with SCI; accounting for level and severity of injury to sympathetic cardiovascular pathways, arterial gas concentrations and symptoms. Our results indicate, for the first time, that cerebral autoregulation is diminished after SCI and that this dysfunction is related to the level and severity of autonomic injury.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Victoria Claydon
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) M.Sc.

Biomechanics of balance recovery by handrail grasping

Date created: 
2011-11-23
Abstract: 

While public transportation continues to grow in relevance, few ergonomic and biomechanical studies have examined passenger safety, especially related to falls from standing, and the role of handrail grasping in balance maintenance. In this thesis, I examined forces from upper limbs (from a load cell), lower limbs (from a force-plate) and muscle responses (from EMG) involved in balance recovery during simulated vehicle acceleration and deceleration pulses. Subjects stood (forward or sideways) on a platform holding a handrail in two different positions (shoulder height and overhead). A linear motor accelerated the platform at high and low perturbation magnitudes. Hand configuration, perturbation direction and perturbation magnitude influenced hand forces, COP displacement and muscle activation. Forward stance while holding the handrail at shoulder height increased the musculoskeletal demands of balance maintenance. Improved knowledge from this project should help guide the design of safer vehicles.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Dr. Stephen Robinovitch
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) M.Sc.

Constitutive activation of Fyn kinase induces dual kinase modulation of the cardiac voltage-gated sodium channel, Nav1.5

Date created: 
2011-11-03
Abstract: 

Ion channels are critical regulators of excitability in neurons and muscle. The cardiac sodium channel, Nav1.5, is responsible for the initial upstroke of the action potential in ventricular myocytes. Post-translational modifications, such as phosphorylation, modulate Nav1.5. During physiological events, constitutive activation of one or more enzymes results in the integration of signal transduction pathways, thereby altering channel modulation. Specifically, previous studies implicate the integration of PKC and Fyn kinase signal transduction pathways. I studied the effects of dual kinase modulation in Nav1.5 by using Fyn kinase (Fyn) and a partially-selective PKC inhibitor, Bisindolylmaleimide-1 (BIM1). Whole-cell voltage clamp experiments were performed using HEK293 cells co-expressing Nav1.5 and either FynCA (constitutively active) or FynKD (kinase dead, which exerts a dominant-negative effect on tyrosine phosphorylation). Cells co-expressing Nav1.5 + FynCA (without BIM1) showed (i) a significant left shift in the mid-point of steady-state fast inactivation, (ii) accelerated rate of fast inactivation, and (iii) increased non-inactivating sodium current, all of which were not seen in Nav1.5 + FynKD (without BIM1), control or Nav1.5 + FynCA + BIM1 experiments. These results indicate that constitutive activation of Fyn (i) confers dual kinase modulation of Nav1.5 and (ii) leads to the hypoexcitability of cells, which may be pro-arrthythmogenic.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Peter Ruben
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) M.Sc.

Investigations into the accumulation of hematopoietic cells in the spinal cord in a murine model of motor neuron disease

Date created: 
2011-08-12
Abstract: 

Transgenic mice over-expressing human mutant superoxide dismutase 1 (mSOD) develop motoneuron loss resembling amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease. Bone marrow (BM) chimeric mice created by myeloablating and transplanting mice with green fluorescent protein (GFP)-labelled BM were used to study the recruitment of BM-derived cells (BMDCs) into spinal cords of mSOD and control mice. Accumulation of GFP+ cells in mSOD spinal cord paralleled disease progression and significantly greater numbers of GFP+ cells were observed in mSOD spinal cord at symptomatic and disease end-stages compared to controls. GFP+ BMDCs expressed the macrophage markers CD11b and F4/80, which are also expressed by microglia. GFP+ BDMCs constituted 10-20% of total CD11b/F4/80 + cells within spinal cord, indicating expansion of microglia within mSOD spinal cord is primarily through proliferation of resident microglia. Analysis of morphology and proximity of BMDCs to blood vessels revealed that only a fraction of BMDCs acquire the stellate morphology and Iba1+ immunophenotype characteristic of parenchymal microglia, and the majority of BMDCs remained in close proximity to blood vessels. Mice transplanted with BM from donors expressing GFP in only CX3CR1+ cells demonstrated that this population of cells accumulates within control and mSOD spinal cord. To determine whether myelosuppressive regimens alternative to irradiation potentiate BMDC accumulation in mSOD and control spinal cord, mice were treated with the chemotherapeutic Busulfex (BU) and transplanted with GFP+ BM. GFP+ cells were observed in spinal cords of mSOD and control mice. Cytotoxic T-cells were also observed in control and mSOD spinal cord, suggesting the dose of BU used in this study has neurotoxic and neuroinflammatory effects. The differential accumulation of CX3CR1+ BM cells and cells derived from definitive hematopoiesis was analyzed by transplanting irradiated mSOD and control mice with the CX3CR1+/GFP fraction of BM cells along with red fluorescent protein (RFP) c-Kit+Lin-Sca1+ cells. Analysis of spinal cord at disease end-stage revealed CX3CR1+/GFP and RFP+ cells in the spinal cords of mSOD and controls, indicating that circulating cells from the CX3CR1+/GFP BM fraction and cells derived from definitive haematopoiesis are accumulate in spinal cord.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Charles Krieger
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Dissertation) Ph.D.