Skeletal muscle fatigue can be defined as the inability to produce a desired amount of force. Fatigue can not only limit athletic performance and rehabilitation, but it can affect one's ability to perform every day activity as well. Despite extensive investigation of muscle fatigue, little is known about the exact mechanisms that result in decreased muscle performance. It likely involves several factors that are themselves dependent upon activation patterns and intensity. The process of excitation-contraction (EC) coupling is of particular importance with respect to regulation of force production. The release of calcium (Ca²⁺) from the sarcoplasmic reticulum (SR), which is stimulated by the depolarization of the sarcolemma, causes muscle contraction. The SR Ca²⁺-adenosine triphosphatase (ATPase) drives the translocation of two Ca²⁺ ions into the SR, utilizing the energy derived from the hydrolysis of one adenosine triphosphate (ATP) molecule. The process of SR Ca²⁺ uptake causes muscle relaxation. It has been proposed that both glycogen and glycolytic enzymes are associated with the SR membrane (SR-glycogenolytic complex). Interestingly, glycogen phosphorylase, an enzyme involved in glycogen breakdown, seems to be associated with the SR-glycogenolytic complex through its binding to glycogen. The presence of the SR-glycogenolytic system may serve to locally regenerate ATP utilized by the SR Ca²⁺-ATPase. The purpose of the present study was to investigate the effects of prolonged muscle contraction on glycogen concentration, glycogen phosphorylase content and activity, and maximum Ca²⁺ uptake rate associated with the SR. Tetanic contractions, elicited once per second for 15 minutes, significantly reduced glycogen associated with SR to 5.1% of control from 401.17 ± 79.81 to 20.46 ± 2.16 mg/mg SR protein (£ 0.05). The optical density of glycogen phosphorylase from SDS-PAGE was significantly reduced to 21.2% of control (£ 0.05). Activity of glycogen phosphorylase, in the direction of glycogen breakdown, was significantly reduced to 4.1% of control (£ 0.05). Pyridoxal 5'-phosphate (PLP) concentration, a quantitative indicator of glycogen phosphorylase content, was significantly reduced to 3.3% of control (£ 0.05). Maximum SR Ca²⁺ uptake rates were significantly reduced to 80.8% of control (£ 0.05). These data suggest reduced glycogen and glycogen phosphorylase may be involved, either directly or indirectly, in a mechanism that causes decreased SR Ca²⁺ uptake normally found in fatigue. / Master of Science

No / We have examined whether melanin affects Ca2+ homeostasis in cultured normal human melanocytes. Intracellular Ca2+ concentrations ([Ca2+]i), were measured in four Caucasian and in three Negroid melanocyte cultures. Under resting conditions [Ca2+]i was around 100 nM in all cultures, but differences between cells within cultures were observed. All cultures responded to endothelin-1 (ET-1) with increases in [Ca2+]i and there were no differences between Caucasian and Negroid cultures. However, large differences in responses between cells within cultures were observed, indicating that melanocyte cultures are very heterogeneous. The addition of 2.5 mM CaCl2 to melanocytes kept in Ca2+-free medium resulted in rapid and transient increases in [Ca2+]i of up to 1500 nM. These increases were on average more than two times smaller in melanocyte cultures established from Negroid donors compared with Caucasian cultures. In addition, well melanized Caucasian melanocytes, cultured in the presence of 400 ¿M tyrosine and 10 mM NH4Cl, showed a reduced increase in cytoplasmic Ca2+ concentration upon the addition of extracellular Ca2+. The difference in maintaining Ca2+ homeostasis between poorly and well melanized melanocytes may be the result of the clearance of cytoplasmic Ca2+ into melanosomes and the greater capacity for this in the more pigmented melanocytes.

Streptococcus pneumoniae (pneumococcus) is a commensal gram-positive colonizer of the human nasopharynx capable of causing diseases including otitis media, pneumonia, bacteremia, and meningitis. Although it is often a harmless colonizer, there is a high rate of mortality and morbidity among the immunocompromised, elderly, and young children. While these infections can often be treated with antibiotics, resistance to numerous antibiotics is increasing. Antibiotic resistance is a well-studied dilemma; however, little information is known of how bacteria take up certain antibiotics. Because most antibiotics cannot diffuse freely across the bacterial cell wall, we hypothesize that metabolite transport proteins participate in the uptake of certain classes of antibiotics.

Atherosclerosis is a disease characterized by cholesterol-rich plaques within the intima of medium and large arteries. Cholesterol deposition is thought to occur by infiltration of low-density lipoprotein (LDL) into lesions followed by uptake into macrophages, generating lipid-loaded “foam cells.” Foam cells can also be generated in vitro by treatment of macrophages with LDL or oxidized LDL (oxLDL). The purpose of the current investigation was to determine the contribution of selective cholesteryl ester (CE) uptake versus whole-particle uptake during LDL-induced foam cell formation in cultured macrophages. Murine bone marrow-derived macrophages (BMMs) exhibited significant cholesterol accumulation when treated with LDL as indicated by quantification of cellular cholesterol and visualization of Oil Red-O-stained neutral lipid droplets. Uptake of LDL cholesterol was determined by measuring uptake of 3H and 125I into BMMs during treatment with [3H]CE/125I-LDL. [3H]CE uptake was linearly related to the LDL concentration at the concentrations used and was much larger than 125I uptake, indicating that the majority of LDL-cholesterol was acquired by nonsaturable, selective CE uptake. This pathway was demonstrated to be independent of whole-particle uptake by showing that inhibition of actin polymerization blocked LDL particle uptake but not selective CE uptake. Analysis by thin-layer chromatography (TLC) indicated that following uptake, [3H]CE was rapidly hydrolyzed into [3H]cholesterol by cells and largely effluxed into the culture medium. In contrast to LDL, studies of [3H]CE/125I-oxLDL uptake demonstrated that CE was acquired from oxLDL by whole-particle uptake with little or no selective CE uptake. Using a series of ten different [3H]CE/125I-oxLDLs oxidized for 0-24 hours, selective [3H]CE uptake was shown to be progressively impaired by LDL oxidation, while 125I-LDL particle uptake was increased as expected. Interestingly, the impairment of selective CE uptake occurred very early in LDL oxidation and this minimally oxidized LDL induced significantly less cholesterol accumulation in BMMs compared to native LDL. Together, these results demonstrate that selective CE uptake is the primary mode of cholesterol uptake from LDL but not oxidized LDL, a finding that has important implications for cholesterol metabolism in atherosclerotic lesions. Future studies seek to identify the molecular components that participate in the macrophage selective CE uptake mechanism.

M. Comm. / Psychiatrists are medical doctors who have specialised in the field of Psychiatry. Psychiatry is one of the five major fields in medicine, the other fields being Surgery, Obstetrics and Gynaecology, Internal Medicine and Paediatrics. Psychiatrists treat psychiatric disorders by way of diagnosis and invariably the prescription of the appropriate medication. Sixty to seventy percent of the diagnoses made by psychiatrists in private practice involve the so-called mood disorders in which a depressed mood is a common occurence. Depression is mostly treated with anti-depressant medication. (Olfson and Klerman , 1993:572). Accumulating evidence suggests that the use of anti-depressant medications is increasing. Sclar et. al. examined data from the National Ambulatory Medical Care Survey for the period 1990 through 1995. American National estimates of the number of office-based visits resulting in a prescription for or continuation of anti-depressant pharmacotherapy for any purpose escalated from 16 534 268 in 1990 to 28 664 796 in 1995, a 73,4% increase. (Sclar, Robinson, Skaer, Galin.1998:870) .although a Medline search cannot produce more recent figures it is commonly accepted that the most widely prescribed anti-depressants today fall in the class known as the SSRI's which stands for selective serotonin reuptake inhibitors. Use of a SSRI for the treatment of depression increased from 37.1% in 1990 to 64.6% in 1995. The first SSRI medication to become available on the South African market was fluoxetine under the trade name of Prozac in late 1987. (Preskorn, 1996: 18). To date approximately 25 million people have used Prozac worldwide. Prozac and other newer anti-depressants have been the topic of lead articles in national news magazines, best-selling books and widely watched television talk shows.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 5 uppsatser.

Cerium oxide nanoparticles (nanoceria) have shown great potential as antioxidant and radioprotective agents for applications in cancer therapy. Recently, various polymer-coated nanoceria preparations have been developed to improve their aqueous solubility and allow for surface functionalization of these nanoparticles. However, the interaction of polymer-coated nanoceria with cells, their uptake mechanism, and subcellular localization are poorly understood. Herein, we engineered polymer-coated cerium oxide nanoparticles with different surface charges (positive, negative, and neutral) and studied their internalization and toxicity in normal and cancer cell lines. The results showed that nanoceria with a positive or neutral charge enters most of the cell lines studied, while nanoceria with a negative charge internalizes mostly in the cancer cell lines. Moreover, upon entry into the cells, nanoceria is localized to different cell compartments (e.g., cytoplasm and lysosomes) depending on the nanoparticles surface charge. The internalization and subcellular localization of nanoceria plays a key role in the nanoparticles cytotoxicity profile, exhibiting significant toxicity when they localize in the lysosomes of the cancer cells. In contrast, minimal toxicity is observed when they localize into the cytoplasm or do not enter the cells. Taken together, these results indicate that the differential surface-charge-dependent localization of nanoceria in normal and cancer cells plays a critical role in the nanoparticles toxicity profile.

No description available.

Master of Science / Department of Kinesiology / Thomas J. Barstow / Purpose: Oxygen uptake (VO2) has been shown to be controlled by a nonlinear system, yet the VO2 response to ramp style exercise appears linear. We tested the hypothesis that an integrative model incorporating nonlinear parameter values could accurately estimate actual VO2 responses to ramp style exercise. Methods: Six healthy, men completed three bouts of varying ramp rate exercise (slow ramp (SR): 15 W/min, regular ramp (RR) 30 W/min, fast ramp (FR) 60W/min) and four bouts of extended-step incremental exercise, where each step lasted 5-15 min or until volitional fatigue on a cycle ergometer on separate days. The step-responses were then fit with a simple monoexponential starting at time zero (MONO) or allowing a time delay and using only the first 5 min of data (5TD). The resulting VO2 parameters from the step protocol were incorporated into an integrative model for the estimation of the VO2 response to each of the rates of ramp incremental exercise. The parameters from the actual and model ramp protocols were compared with 2 way repeated-measures ANOVAs. Results: Both Gain (G) and Mean Response Time (MRT) (or time constant) values increased significantly across work rate transitions (mean±SD; Gain:10.0±0.9, 11.6±1.1, 13.1±1.3, 17.6±3.3 ml O2/min/W; MRT:39.4±7.7, 54.0±5.4, 79.6±15.0, 180.1±56.2 s). Up to maximalVO2 the models over-estimated the actual VO2 response for FR (Gain: ACT 8.7±1.0, MONO 9.9±0.4, 5TD 10.3±0.3 ml O2/min/W). Up to 80% maximal VO2 the models accurately predicted the actual VO2 response across all ramp rates (Gain: ACT 10.7±1.1, 10.2±0.5, 9.2±1.0; MONO 11.0±0.8, 10.3±0.6, 9.2±0.5; 5TD 10.4±0.4, 10.2±0.3, 9.8±0.2 ml O2/min/W, values are listed SR,RR,FR). Conclusions: When variable parameter values (G and either MRT or time constant and time delay) were utilized by an integrative model, accurate estimations of the VO2 response to ramp incremental exercise were possible regardless of ramp rate (up to 80% maximal VO2). The increases in both G and MRT (or time constant) appear to balance each other to produce the quasi-linear VO2 responses.

This study examines three possible methods for improving the digestibility and bioavailability of zinc to rainbow trout (Oncorhynchus mikiss). The first method was to examine the availability of the zinc utilisation from commonly used protein sources; the second was to assess the efficacy of the upstream use of an enzyme treatment of the raw materials; the third was to assess the use of organically complexed mineral supplements as opposed to the inorganic salts widely used at present. The first section indicated that the zinc from the soyabean meal was the most available (49.4%). The zinc digestibilities of the animal based protein used in this current study were 15.1% for LT94 fish meal, 26.6% for the Provimi 66 white fishmeal and 15.8% for poultry meat meal. The zinc in the maize/corn gluten meal was 31.9% digestible and from the NuPro 26.1%. Gram for gram maize gluten meal supplied the least amount of zinc to the fish (3.66 mg per kg). Based on these results the diets for the subsequent supplementation trials were formulated. The liver, eye and caudal fin were identified biomarkers of a severe zinc deficiency. The second part of the study revealed a soybean product, treated by exogenous enzymes, had a higher phosphorus digestibility, (49.0%, vs. 36.6%) and zinc digestibility (30.7% vs. 7.9%) The treatment did not improve the protein digestibility (85%). The third part of the study showed the organic source proved more digestible than the inorganic, 37.4% and 26.9% respectively. The fish fed the organic source maintained a higher level of zinc in both the eye and caudal fin. The liver zinc levels were unaffected by both dietary level and zinc source. Analysis of the liver for a zinc dependant protein showed that under stress conditions only the organic supplemented fish were able to synthesis this protein. The analysis of the mRNA levels coding for this protein indicate the fish on both zinc forms up regulated the production of the mRNA to the same extent when stressed. Finally this study also examined the viability of using a stable isotope to identify different ‘preferences’ for one form of supplementation over the other in different tissues. This method illustrated a tissue dependant difference to how the fish attempted physiologically to compensate for zinc deficiency. The rate of turnover was fastest in the liver, then the caudal fin and then the eye, and also showed that when the diet was more deficient there was an increased ability for the tissues to take up the organic form.