Creatine kinase (CK) primarily serves as an energy buffer assisting in regulating ATP homeostasis through synthesis of ATP from ADP and phosphocreatine (PCr). This enzyme is bound in the sarcomere near sites of ATP consumption via acto-myosin ATPase (A‧M‧ATPase) and research in cardiac muscle has found that PCr can alter contractile performance (maximal isometric force and Ca²⁺ sensitivity). Based on this evidence, CK and A‧M‧ATPase may be coupled in skeletal muscle. Therefore the purpose of this investigation was to determine the influence of the CK system on contractile performance and energy utilization in skeletal muscle. When skinned fibers (membrane removed) were provided a limited supply of [ATP] (0.1 mM), this resulted in increased Ca²⁺ sensitivity. The addition of PCr to low ATP solutions restored Ca²⁺ sensitivity and allowed normal isometric force generation across a range of [Ca²⁺] via ATP synthesis by CK. This was also possible with only CK reaction substrates (ADP, PCr) in the absence of ATP. Based on these findings, endogenous CK activity in glycerol skinned skeletal muscle fibers is sufficient to permit normal function of the contractile apparatus. Energy utilization was studied by indirect assessment of ADP production. Decreased net ADP production as measured by NADH fluorescence revealed endogenous CK was able to convert ADP produced by A‧M‧ATPase to ATP in skeletal muscle across a range of both [Ca²⁺] and [ATP]. This was confirmed directly via high-performance liquid chromatography measurements of ATP and ADP by showing that skinned skeletal muscle bundles have sufficient endogenous CK activity to produce ATP from substrates (ADP, PCr) and the ability to maintain low [ADP] in the presence of PCr. This study adds to the evidence for specific compartmentation of CK near sites of ATP utilization and contributes to the body of knowledge on contractile performance in skinned skeletal muscle fibers. By showing how changing demands on skeletal muscle (through increased Ca²⁺) alters force production and Ca²⁺ sensitivity, these findings lend support for the importance of endogenous CK as a pathway of ATP regeneration in skeletal muscle. / Ph. D.

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Thesis advisor: David Burgess / The contractile ring is pictured, analyzed, and even named under the basic assumption that the geometry of the structure begins and ends circularly and the ring is a single homogenous structure acting uniformly. However, under physiological conditions cell-to-cell adhesions force cells and therefore initial contractile rings into highly irregular and noncircular shapes. To investigate this basic assumption of contractile ring geometry, contractile ring shape of dividing sea urchin embryos was analyzed under three conditions: in seawater where cell-to-cell adhesion is strong, calcium free seawater where cell-to-cell adhesion is minimized, and in microfabricated chambers to artificially manipulate the initial contractile ring shape. We found that contractile ring geometry evolves over time to become circular even when it begins as an irregular shape due to cell-to-cell adhesions or artificial manipulation. By analyzing velocities of specific regions of the contractile ring, it became apparent that there is always a pattern of rounding regions of lowest circularity before overall ring contraction. This pattern suggests that the contractile ring is capable of producing varying forces in a coordinated manner. Therefore the contractile ring can not only be noncircular, but can also possess regions with different molecular and biophysical properties. / Thesis (MS) — Boston College, 2016. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Biology.

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Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

<p> We hypothesized that acute inhibition of the contraction-induced expansion of the muscle TCA cycle intermediate (TCAI) pool via would not adversely effect metabolism or contractile function. Forty rats were anaesthetized and the gastrocnemius muscle (GAS) from one leg was vascularly isolated and perfused with saline (CON) or a red cell media containing DL-cycloserine (CYCLO; Sigma C-7005; dose=0.05 mg/g), an inhibitor of alanine aminotransferase (AAT). After 1h of perfusion, the GAS muscle was either snap frozen (CON-Rest, n=11; CYCLO-Rest, n=9) or stimulated to contract for 10 min (1Hz, 0.3 ms, 2 V) with blood flow fixed at 30 ml min-1 100g-1 and then snap frozen (CON-Stim, n=10; CYCLO-Stim, n=10). The maximal activity of AAT was lower (P≤0.05) at both CYCLO-Rest (0.61±0.02 mmol·kg-1w.w./min; mean± SEM) and CYCLO-Stim (0.63±0.01 mmol·kg-1w.w./min) vs CON-Rest (3.56±0.16 mmol·kg-1w.w./min) and CON-Stim (3.92±0.29 mmol·kg-1w.w./min). Consistent with lower net flux through AAT, muscle [alanine] was lower (P≤0.05) after CYCLO-Stim (6.97±0.26 mmol·kg-1 dw) compared to CON-Stim (8.55±0.56 mmol·kg-1 dw) and not different vs CON-Rest (6.79±0.41 mmol·kg-1 dw). The sum of five measured TCAI (malate, fumarate, citrate, isocitrate, and 2-oxoglutarate) was higher (P≤0.05) at both CON-Rest (2.10± 0.09 mmol·kg-1 dw) and CON-Stim (2.48± 0.11 mmol·kg-1 dw) vs CYCLO-Rest (1.56± 0.11 mmol·kg-1 dw) and CYCLO-Stim (1.88± 0.15 mmol·kg-1 dw) respectively. Despite the reduction in [TCAI] following CYCLO treatment, there was no difference between conditions in muscle lactate accumulation or phosphocreatine degradation after 10 min of stimulation. Contractile function was not different (P≤0.05) between conditions at either rest or stimulation and the decline in force production over ten minutes of stimulation was identical (~60%) between CON-Stim and CYCLO-Stim respectively. We conclude that flux through AAT was reduced after cycloserine treatment, however the acute inhibition of TCAI expansion did not compromise aerobic energy provision. These data support the hypothesis that the contraction-induced increase in muscle [TCAI] is not causally linked to oxidative energy delivery.</p> / Thesis / Master of Science (MSc)

Pelvic organ prolapse, the decent of the pelvic organs from their normal anatomical position, is a common condition among women that is associated with mechanical alterations of the vaginal wall. In order to characterize the complex mechanical behavior of the vagina, we performed planar biaxial tests of vaginal specimens in both the passive (relaxed) and active (contracted) states. Specimens were isolated from virgin, female Long-Evans rats (n=16) and simultaneously stretched along the longitudinal direction (LD) and circumferential direction (CD) of the vagina. Tissue contraction was induced by electric field stimulation (EFS) at incrementally increasing values of stretch and, subsequently, by KCl. On average, the vagina was stiffer in the CD than in the LD (p<0.001). The mean maximum EFS-induced active stress was significantly higher in the CD than in the LD (p<0.001). On the contrary, the mean KCl-induced active stress was lower in the CD than in the LD (p<0.01). When comparing the mean maximum EFS-induced active stress to the mean KCl-induced active stress, no differences were found in the CD (p=0.404) but, in the LD, the mean active stress was much higher in response to the KCl stimulation (p<0.001). Collectively, these results demonstrate that the anisotropic behavior of the vaginal tissue is determined not only by the collagen and smooth muscle fiber organization but also by the innervation. The findings of this study may contribute to the development of more effective treatments for pelvic organ prolapse. / MS / Pelvic organ prolapse (POP), the decent of the pelvic organs from their normal anatomical position, is a common condition among women that is associated with alterations of the mechanical properties of the vaginal wall. The characterization of the mechanical properties of the vagina is crucial for the development of effective treatments for POP. Biaxial tensile tests were performed in this study so we could observe the behavior of the vagina along both the circumferential direction (CD) and the longitudinal direction (LD). In these tests, square specimens were secured along all four edges and pulled outward such that we could observe the relationship between the stretch and the stress that the tissue experienced. Additionally, because the vagina contains smooth muscle, we also tested the tissue in its active, or contractile state at each stretch level. Contractions were induced by applying electric field stimulation (EFS) to observe nerve-mediated responses, and subsequently by potassium chloride (KCl). On average, the vagina was stiffer in the CD than in the LD (p<0.001). The mean maximum EFS-induced active stress was significantly higher in the CD than in the LD (p<0.001). On the contrary, the mean KCl-induced active stress was lower in the CD than in the LD (p<0.01).

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Diabetes is considered a major threat to human health in both developed and developing nations. Cardiovascular disease which is common in diabetic patients has increased the overall disease affliction. Moreover, stress-induced hyperglycemia has led to increased mortality and morbidity in patients with an acute myocardial infarction (MI), whether the patient has diabetes or not. In addition, acute MI might stem from stress-induced hyperglycemia capability to increase inflammation and oxidative stress resulting in a worse functional cardiac outcome. Hyperglycemia-induced oxidative stress can similarly result in the formation of miss folded or damaged proteins that may be eliminated by the ubiquitin-proteasome system (UPS). Futhermore, hyperglycemia-induced oxidative stress can also result in dysregulation of the UPS that removes these misfolded proteins. Additionally, an increasing body of evidence implicates UPS dysfunction in cardiac diseases and hyperglycemia which has been associated with increased inflammation and blunted cardiac function in response to ischemia-reperfusion. Literature however is blurred whether a reduction or a rise in the UPS is damaging with hyperglycemia and in response to ischemia-reperfusion. In light of this, we hypothesized that UPS inhibitors such as Z-Leu-Leu-Leu-al (MG-132) and lactacystin, protects the rat heart against ischemia-reperfusion under hyperglycemic perfusion conditions. Isolated rat hearts were perfused ex vivo with Krebs-Henseleit buffer containing 33 mM glucose vs. controls (11 mM glucose) for 60 min, followed by 20 min global ischemia and 60 minutes reperfusion ± PI treatment (MG-132 and lactacystin), anti-inflammatory (Ibuprofen) and anti-oxidant (NAC). Infarct size was determined using Evans Blue dye and 1% 2,3,5-triphenyl tetrazolium chloride (TTC) staining with 20 minutes regional ischemia and 2 hours reperfusion ± PI’s treatments. Tissues were collected at the end of the global ischemia experiments and analyzed for UPS activity, oxidative stress, apoptosis and inflammation. Our data expressed a reduced cardiac contractile function in response to ischemia and reperfusion under hyperglycemic conditions as well as an increase in UPS activity. PI treatment resulted in cardio-protection for ex vivo rat heart model exposed to ischemia and reperfusion under hyperglycemic conditions as well as ibuprofen and NAC. In parallel lactacystin treatment significantly decreased myocardial oxidative stress, apoptosis, and inflammation which provided cardio-protection in response to ischemia and reperfusion under hyperglycemic conditions This study shows that acute hyperglycemia elicits myocardial oxidative stress, apoptosis and inflammation that in time results in an increase in contractile dysfunction following ischemia and reperfusion. However, we found that PI treatment with both MG-132 and lactacystin blunted high glucose-induced damaging effects which resulted in a robust cardio-protection in response to ischemia and reperfusion under hyperglycemic conditions, by reducing oxidative stress, decreasing apoptosis and limiting inflammation. A parallel outcome was observed at baseline although the underlying mechanisms driving this process still need to be clarified. Our findings indicate that the UPS may be a unique therapeutic target to treat ischemic heart disease in diabetic patients, and non-diabetic individuals that present with stress-induced hyperglycemia. In summary, this thesis established that PIs act as a novel cardio-protective intervention to treat acute hyperglycemia with associated cardiovascular complications. / AFRIKAANSE OPSOMMING: Diabeties word beskou as ‘n baie groot problem vir menslieke gesondhied vir biede die ontwikkel en onontwikkelende lande. Kardiovaskulêre siekte wat normaal met diabetiese pasiente geassoseerd word veroorsaak ‘n toeneemende druk, wat hierdie siekte laat toeneem. Verder meer vergroot stresgeïnduseerde hiperglukemie die mortaliteit van pasiente met of sonder diabeties wat akute miokardiale infarksie onder lede het. Akute miokardiale infarksie kan ook ontstaan van stresgeïnduseerde hiperglukemie se bekwaamheid om meer inflamasie en oksidante stress te veroorsaak wat in ‘n meer swakker funksionele kardiale toestand. Hiperglukemiegeïnduseerde oksidatiewe stres ook tot wanregulering van die ubikwitien-proteosoomsisteem (UPS) wat wangevoude protïene verwyder, aanleiding gee. Kontrasterende data bestaan van verhoogde/verlaagde UPS aktiwietiet, sowel as met hiperglukemie en/of in reaksie tot isgemie-reperfussie. As gewolg hiervan,, hipotetiseer ons dat Z-Leu-Leu-Leu-al (MG-132) and lactacystin as ‘n nuwe kardiobeskermingsmiddel kan optree deur miokardiale oksidatiewe stress, inflamasie en UPS aktiwiteit te verlaag in reaksie op isgemie-reperfussie tydens akute hiperglukemiese toestande kan verlaag. Geïsoleerde rotharte is ex vivo met Krebs-Henseleit buffer, wat, 33 mM glukose vs. kontrole (11 mM glukose) bevat, vir 60 min geperfuseer, daarna is dit deur 20 min globale isgemie gevolg en 60 min reperfussie ± PI behandeling (MG-132 and lactacystin), antiflammatoriese behandeling (Ibuprofen) en antioxidant behandeling (NAC). Infarkgrootte is bepaal deur Evans bou kleursel en 1% 2. 3-5 tripfeniel tetrazoloimcholierd (TTC) kleuring met 20 minute regionale ischemie, en 2 uur reprefussie ± PI’s behandeling. Weefsels is aan die einde van die globale isgemie eksperimente versamel, en vir oksidatewe stres, apoptose en inflammasie ontleed. Ons data toon aan dat kardiale kontraktiele funksie in reaksie op isgemie-reperfussie onder hiperglukemiese toestande verlaag het asook ‘n toename in UPS aktiwitiet veroorsaak. PI behandeling het gelei tot kardiale beskerming vir ex vivo rotharte wat aan isgemie-reperfussie onder hiperglukemiese toestande blootgestel was sowel as ibuprofen en NAC. Parallel hiermee het lactacystin oksidatiewe stres, apoptose, inflmasie, en UPS aktiwiteit na isgemie-reperfussie, verlaag in reaksie isgemie-reperfussie onder hiperglukemiese toestande. Hierdie studie het bevind dat akute hiperglukemie, miokardiale oksidatiewe stres lei tot oksidante stress, apoptose, en inflamasie na kontraktiele wanfunksionering na isgemie-reperfussie lei. Ons het bevind dat beide MG-132 en lactacystin behandeling, hoë glukose-geïnduseerde skadelike effekte onderdruk, en kardiale-beskerming in reaksie op isgemie-reperfussie onder hiperglukemiese toestande ondervind was deur oksidante stress, apoptose, en inflamasie te verlaag. ‘n Soorgelyke effek is tydens die basislyn waargeneem, alhoewel die onderliggende meganisme wat hierdie proses meer ondersoek instel. Ons bevinding dei dat die UPS ‘n nuwe behandeling teiken kan word in sgemie-geïnduseerde reperfussie onder aktute en chroniese hoë glukose toestande. In opsomming, het die tesis belowend bevindinge gevind wat ‘n nuwe terapeutiese intervensie vir die behandeling van akute hiperglukemie met geassosieërde kardiovaskulêre komplikasies gebruik kan word.

Animals, fungi, and amoebas require an actomyosin contractile ring at the division site to perform cytokinesis. The contractile ring initiates and guides the invagination of the plasma membrane as it forms new barriers between the nuclei at the cell equator. Defects in the contractile ring can result in misdirected, delayed, or premature cytokinesis, which leads to abnormal chromosome numbers. Aneuploidies resulting from failed cytokinesis sometimes lead to aggressive forms of cancer. This dissertation was motivated by the goal of better understanding the properties of the contractile ring and how it drives cytokinesis. Actomyosin is initially recruited to the cell equator through the coordination of scaffolding factors, actin-binding proteins, and signaling cascades. Subsequently, the sliding of actin filaments by myosin reshapes the resulting meshwork into a compact ring. Once fully assembled, the contractile ring establishes tension, which leads the plasma membrane inward. The primary motor proteins in the contractile ring of animal cells are class-II nonmuscle myosins, which typically function as bipolar filaments. Filament assembly is activated by phosphorylation and plays a central role in myosin function during cytokinesis. However, many underlying processes that regulate contractile ring function are poorly understood. Current models of cytokinesis have been based on mechanistic insights provided by two decades of work in the fission yeast system Schizosaccharomyces pombe. In fission yeast, the class-II myosin Myo2 provides the major source of motor activity in the contractile ring. Myo2 is two-headed and has a rod-like tail, which is consistent with other class-II myosins. Yet, it was unknown whether Myo2 assembles into filaments, or how phosphorylation affects its activity. To investigate these features, recombinant Myo2 was purified from the baculovirus/Sf9 insect cell expression system. Hydrodynamic measurements were used to examine whether Myo2 forms filaments. These sedimentation velocity data gave no indication that Myo2 self-assembles under the typical physiological salt concentrations, which suggests that Myo2 is unlike any class-II myosin known to date. Myo2 was also treated in vitro with its native kinase Pak1. Phosphorylation of Myo2 molecules had no effect on self-assembly, however it reduced actin-binding in motility assays and increased steady-state ATPase rates by two fold. Our results imply that the function and regulation of fission yeast Myo2 during cytokinesis depends on a specific scaffolding scheme at the plasma membrane, which has not been observed in other eukaryotes. Another interest of this dissertation was how the contractile ring is regulated during cytokinesis. We examined one cytokinesis protein, Cyk3, believed to mediate between the ring and extracellular processes. Genetics and live cell imaging analyses indicated that Cyk3 functions through a catalytically-inactive enzyme domain, which implicated Cyk3's involvement in one of the primary cytokinesis signaling pathways. This dissertation sheds new light on core aspects of how fission yeast undergo cytokinesis, especially with respect to the mechanism of Myo2 activity in the contractile ring. Characterizing the physical and enzymatic properties of an essential myosin in a simple organism should provide insights into cytokinesis in higher organisms.

Environmental temperature exhibits profound effects on the activity and ecology of ectotherms through its impact on muscle contractile physiology. While the performance of locomotor behaviors powered by muscle contraction directly decreases by at least 33% over a 10°C drop in body temperature, chameleons are known to feed, presumably with high performance, at body temperatures where sympatric lizard species remain inactive. I propose that ballistic movements that are powered by the recoil of preloaded elastic and collagenous tissues are less thermally dependent than movements that rely on direct muscular power. Despite the reduced thermal sensitivity of the elastic-recoil powered movement, I propose that the muscles associated with preloading these elastic tissues are themselves thermally sensitive and at low temperature, will take longer to load the elastic tissues. Finally, I expect that because of the different effect of temperature on elastic-recoil-powered and muscle-powered movements, performance declines for elastic-recoil-powered tongue projection at low temperature will not vary between species along an environmental temperature gradient (i.e., thermal effects will be the same for all species). Conversely, performance declines for muscle powered tongue retraction at low temperature will be lower in species from colder environments along an environmental temperature gradient. To test these predictions, I used high-speed videography, electromyography and in vitro muscle contractile experiment techniques in conjunction with temperature manipulations to test the mechanistic principles in Chamaeleo calyptratus. I then used high-speed videography at different temperatures in three Bradypodion species from different habitats in South Africa to compare thermal effects on elastic-recoil and muscle-powered movements in different species. I found that the elastic-recoil mechanism of tongue projection in chameleons circumvents the constraints that low temperature imposes on muscle rate properties, thereby reducing the thermal dependence of tongue projection. In all species examined, tongue projection was relatively thermally robust, maintaining a high degree of maximal performance at temperatures as low as 15°C. In contrast, the associated muscle-powered tongue retraction was strongly effected by temperature and experienced substantial performance declines over the same temperature range. While tongue projection performance was itself thermally robust, muscle contractile dynamics of the tongue projector muscle, which preloads the elastic elements responsible for powering projection, was strongly affected by temperature. Similarly, at cooler temperatures the tongue projector muscle became active earlier relative to the onset of tongue projection, due to the reduced rate of tension buildup and the resulting increase in time required to load the elastic elements of the tongue with the required force to subsequently power tongue projection. Further, the effect of temperature on both tongue projection performance and tongue retraction performance was found to vary between species living in different thermal environments. This suggests that despite differences in how temperature affects the performance of these different movement types, both elastic-recoil-powered movements and muscle-powered movements may experience selective pressure to optimize their performance to their environments. Based on these findings, I suggest that the relative thermal independence of tongue projection in chameleons is a more general characteristic of elastic-recoil-powered mechanisms and organisms that use elastic recoil mechanisms for ecologically important movements, such as feeding and locomotion, may benefit from an expanded thermal niche. Further, given the prevalence of elastic power-amplification mechanisms in ectotherms, the benefit of reduced thermal sensitivity may promote the evolution of these mechanisms in other ectothermic animals. Finally, I propose that temperature manipulations may be a useful methodological approach to testing for the presence or prevalence of elastic recoil in powering other biomechanical systems. While these studies examined thermal effects on ballistic tongue projection and tongue retraction in chameleons at difference mechanistic levels and within the framework of how these thermal relationships may be affected by their local environment, many of the results apply more broadly to similar systems in other ectotherms. Comparison of these findings to similar elastically powered systems may help solidify the generality of these findings among other taxa.