The experiments described in this thesis comprise a series of related, yet independent investigations examining the physiological and metabolic responses of well-trained amateur cyclists under conditions designed to mimic actual competitive situations, during individual and mass start races. In Section A the physiological responses to constant load and steady state exercise are determined. In Section B, the metabolic factors associated with constant and variable load cycling performance are examined.

Ca2+-binding proteins (CaBP) alter Ca2+ signals, triggering cellular processes such as gene transcription regulation in neurons. CaBP1/CD is a calmodulin (CaM)-like Ca2+ binding protein that may regulate neuronal functions through interactions with effectors such as voltage-gated Ca2+ (Cav) channels and inositol trisphosphate receptors (InsP3Rs). To gain insight into the potential cellular functions of CaBP1/CD, we analyzed the expression and localization of CaBP1/CD variants in mouse brain. Of the three CaBP1/CD splice variants that have been characterized (CaBP1-S, CaBP1-L, and caldendrin (CD)), CD was the major variant expressed in mouse brain by western blot and quantitative polymerase chain reaction. These results reflected the expression of CaBP1/CD since they were not reproduced in mice with targeted disruption of the gene encoding CaBP1/CD (CaBP1 knock-out). By immunoperoxidase labeling, CaBP1/CD was localized in multiple cell-types including pyramidal cells in the cerebral cortex and hippocampal CA3 neurons and inhibitory neurons in the cerebellum. In the cerebellum, CaBP1/CD was not detected in Purkinje neurons but strongly colocalized with voltage-sensitive Shaker-type potassium channel, Kv1.2, in the pinceau formation formed between basket cells and the Purkinje cell axon initial segment. We conclude that CaBP1/CD is expressed in a subset of principal neurons where it may regulate Ca2+ signaling and neuronal excitability.

African runners dominate distance running both in South Africa and internationally. Therefore, the aim of this thesis was to compare selected exercise and skeletal muscle characteristics in well-trained African and Caucasian 10 km runners to determine if evidence exists of differences between these groups with respect to these physiological and biochemical characteristics. Furthermore, the relationship between exercise and skeletal muscle characteristics was investigated. Sedentary individuals from each population group were also studied to determine if differences existed in untrained skeletal muscle between groups. Maximal oxygen consumption and peak treadmill speed were measured using an incremental treadmill protocol whilst submaximal exercise characteristics were measured during a specifically designed protocol consisting of four sequential submaximal workloads relative to the peak treadmill speed of the individual. The final workload was maintained until fatigue with resistance to fatigue defined as total test time. Running economy was measured at a treadmill speed of 16.1 km/hr. Race pace characteristics were measured directly at race pace. Characteristics measured during exercise tests were oxygen uptake, minute ventilation, respiratory exchange ratio and heart rate whilst plasma lactate concentration was determined immediately after exercise. Skeletal muscle characteristics were determined by needle biopsy of the vastus lateralis muscle. Skeletal muscle enzymes citrate synthase, phosphofructokinase, 3-hydroxyacyl CoA dehydrogenase, hexokinase and carnitine palmityl transferase were assayed spectrophotometrically. Skeletal muscle buffering capacity was measured using by titration and fibre type proportions were analysed histochemically. Comparisons between groups were made with the Student's t-test for unpaired data whilst the relationships between variables were analysed using the Pearson's correlation coefficient. The first major finding was that when exercising at the same relative percentage of individual maximal treadmill velocity, African distance runners were able to exercise for longer than the Caucasians (1376±227 vs 1137±126 sec, p<0.01) with lower plasma lactate accumulation (4.8±3.2 vs 7.7±2.8 mmol/l,p<0.05). Time to fatigue was significantly related to a lower plasma lactate concentration (r=-0.63) and a lower respiratory exchange ratio (r=-0.53). The second major finding indicated that African runners were able to race 10 km at a higher percentage of their maximal oxygen uptake (93.5 vs 86.0%, p<0.005), whilst eliciting only a comparable plasma lactate concentration and respiratory exchange ratio. The third main finding was that the African runners were more economical than the Caucasian runners (p<0.05). The fourth main finding is that the African runners had a 50% greater activity of citrate synthase (p<0.005) and 3-hydroxyacyl CoA dehydrogenase (p<0.01) in the vastus lateralis than the Caucasians and this could not be explained by fibre type proportions, because the proportion of type I fibres was lower in the African runners (p<0.05). Citrate synthase activity, was related to the runners' ability to resist fatigue at high intensity relative to their individual peak treadmill velocity (r=0.70, p<0.05). A higher CS activity was related to a lower plasma lactate concentration and a lower RER. The sixth main finding of this thesis was that skeletal muscle buffering capacity of the Caucasian runners was higher than that of the African runners (p<0.05). A methodological study of buffering capacity in rats showed the buffering capacity was largely dependent upon fibre type and protein concentration, however these parameters could not explain the difference observed between the African and Caucasian runners. Furthermore, despite the differences in skeletal muscle characteristics observed between African and Caucasian runners in the current thesis, there was no evidence of these differences being inherently present in sedentary African and Caucasian individuals. In conclusion, the current series of studies do provide evidence of differences in selected exercise and skeletal muscle characteristics between African and Caucasian distance runners, with the African runners possessing exercise and skeletal muscle profiles that are considered to be more advantageous for endurance performance.

Glycogen depletion has frequently been shown to result in a decrease in respiratory exchange ratio (RER). However, the metabolic response to glycogen depletion has generally been studied in overnight fasted subjects or in subjects who were already fatigued, or hypoglycaemic, or both, raising the question of whether the differences seen were due to general "carbohydrate deficiency" or due specifically to muscle or liver glycogen depletion. If euglycaemia and especially hyperglycaemia is maintained, the " carbohydrate deficiency" is overcome. In addition, because insulin stimulates muscle glucose uptake and not liver glucose uptake during euglycaemia (except at very high concentrations), insulin infusion would differentiate between liver and muscle glycogen depletion, since if the decrease in RER previously observed is abolished with insulin infusion while euglycaemia is maintained, this would indicate that the decrease is specifically due to muscle glycogen depletion. Thus, the aim of this study was to investigate the metabolic effect of glycogen content while an adequate amount or an excess of carbohydrate was provided in the form of an intravenous glucose infusion and when plasma insulin concentrations are raised.

Bibliography / Thesis (MScMedSc (Biomedical Sciences. Medical Physiology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Male infertility is often associated with impaired sperm motility and morphology (asthenoteratozoospermia) for which there is no specific therapeutic treatment. It has come to light that the modification and expression of human sperm proteins play a crucial role in sperm function. In the present study, we present proteomic data of human spermatozoa in the context of sperm dysfunction. Novel techniques have been used to successfully isolate and identify differences in protein expression on a cellular level associated with asthenoteratozoospermia. In the first part of the study, differences in protein expression within the total sperm proteome were investigated between immature and mature sperm populations. Semen was collected from healthy donors (n=23) and separated into mature and immature sperm populations by 3-layer Percoll gradient centrifugation. Cells were washed and motility and morphology were measured by computer assisted sperm analysis (CASA). For the proteomic investigation cells were lysed and proteins separated by means of two-dimensional gel electrophoresis (2D electrophoresis). PD-Quest was used to identify the differentially expressed proteins. The protein spots of interest were excised and subjected to in-gel digestion. Peptides were separated by High Pressure Liquid Chromatography (HPLC) analysis and amino acid sequences determined by mass spectrophotometry. Proteins were identified by Mascot, using the Swiss Prot database. The results show that the motility (immature; 26.1±1.75% total motile cells vs. mature; 60.93±3.24% total motile cells; p<0.001) and morphology parameters (immature; 64.1±2.75% normal head morphology vs. mature; 87.63±3.24% normal head morphology; p<0.001) of the two populations differed significantly. After 2D electrophoresis, 16 differentially expressed protein spots were identified within the total sperm proteome between the immature and mature sperm populations. 56% of the differentially expressed proteins were more abundant in the immature sperm population compared to the mature sperm population. Functions have been ascribed to these proteins of which only four proteins, namely Tubulin -3C/D chain, Tubulin -2C chain, Outer dense fibre protein 2 and A-Kinase anchoring protein 4 precursor, were directly related to sperm motility and morphology. In the second part of the study the expression of nuclear proteins in human spermatozoa was investigated between immature and mature sperm populations. Semen was collected from healthy donors (n=156) and further separated from the seminal plasma by PureSperm® gradient centrifugation. The immature and mature sperm populations were retrieved and used during further analysis. For the proteomic analysis of nuclear proteins, cells were fractionated into four different subcellular protein fractions, instead of analyzing the whole sperm proteome. The results show that the motility (immature; 32.33±0.51% total motile cells vs. mature; 88.67±0.85% total motile cells; p<0.0001) and morphology parameters (immature; 13.51±0.87% normal head morphology vs. mature; 20.89±1.20% normal head morphology; p<0.0001) of the two populations differ significantly. After 2D electrophoresis, 21 differentially expressed nuclear proteins were identified between the immature and mature sperm populations. 95% of the differentially expressed nuclear proteins were less abundant in the immature population compared to the mature population. Only one nuclear protein namely 78kDa Glucose regulated protein was more abundant in the immature population compared to the mature population. Functions ascribed to these individual proteins were directly related to sperm motility, morphology and energy metabolism. In conclusion,In conclusion, in the current study novel techniques have been employed to investigate protein differences between immature and mature sperm populations. From these results it is evident that protein expression in the total sperm proteome and nuclear protein fraction is significantly different and incomplete in the immature population, compared to mature population. Based on these findings, it is recommended that further studies should be done on human spermatozoa to validate the role of the individual proteins in sperm function. Proteomics is an ideal tool to identify idiopathic causes of male infertility, as it can help to identify novel receptors (and signal transduction pathways) that can be used in the screening of drugs to alleviate sperm dysfunction. / AFRIKAANSE OPSOMMING: Manlike infertiliteit word dikwels geassosieer met verlaagde sperm motiliteit en morfologie (asthenoteratozoospermia) waarvoor daar tot dusver nog geen spesifieke terapeutiese behandeling is nie. Dit het aan die lig gekom dat die modifisering en uitdrukking van menslike sperm proteïene ‘n belangrike rol speel in spermfunksie. In die huidige studie stel ons data voor van proteiene in menslike sperme in die konteks van abnormale spermfunksie. Unieke tegnieke was gebruik om verskille in proteïen uitdrukking op sellulêre vlak suksesvol te isoleer en identifiseer wat verband hou met asthenoteratozoospermia. Tydens die eerste deel van die studie was verskille in proteïen uitdrukking binne die totale spermproteoom tussen onvolwasse en volwasse spermpopulasies ondersoek. Sperme van gesonde skenkers (n=23) is geskei in twee spermpopulasies (onvolwasse en volwasse sperme) deur middel van ‘n 3-laag Percoll gradiënt sentrifugasie tegniek. Selle is gewas en sperm motiliteit en morfologie is gemeet deur rekenaar geassisteerde sperm analise (CASA). Vir proteomiese analise is selle geliseer en proteïene geskei deur twee dimensionele gel elektroforese (2D-elektroforese). PD-Quest sagteware is gebruik om statisties beduidende proteïen verskille aan te dui. Die proteïene van belang is uitgesny en onderwerp aan in-gel vertering. Peptiede is geskei met behulp van hoë druk vloeistof chromatografie (HPLC) analise en aminosuurvolgordes is bepaal deur massa spektrofotometrie. Proteïene is geïdentifiseer met behulp van Mascot deur van die Swiss Prot databasis gebruik te maak. Die resultate toon dat die sperm motiliteit (onvolwasse; 26.1±1.75% totale motiele selle vs. volwasse; 60.93±3.24% totale motiele selle; p <0,001) en morfologiese parameters (onvolwasse; 64.1±2.75% normale kop morfologie vs. volwasse; 87.63±3.24% normale kop morfologie; p <0,001) tussen die twee populasies beduidend verskil. Na 2Delektroforese is 16 proteïen kolle geïdentifiseer wat beduidend verskil het, tussen die totale sperm proteoom van onvolwasse spermpopulasies en volwasse spermpopulasies. 56% van die proteïene wat beduidend verskil het, was meer uitgedruk in die onvolwasse spermpopulasie ten opsigte van die volwasse sperm populasie. Funksies is toegeskryf aan hierdie proteïene waarvan net vier proteïene naamlik Tubulin -3C/D ketting, Tubulin -2C ketting, Buite digte vesel proteïen 2 en A-Kinase anker proteïen 4 voorloper direk verband hou met sperm motiliteit en morfologie. In die tweede deel van die studie is die uitdrukking van nukluêre proteïene in menslike spermatozoa tussen onvolwasse en volwasse spermpopulasies ondersoek. Sperme was van gesonde skenkers (n=156) versamel en verder geskei van seminale plasma deur middel van ‘n PureSperm® gradiënt sentrifugasie tegniek. Vir die proteomiese analise van nukluêre proteïene is selle gefraksioneer in vier verskillende sub-sellulêre proteïen fraksies, in plaas van analise van die totale spermproteoom. Die resultate toon aan dat die sperm motiliteit (onvolwasse; 32.33±0.51% totale motiele selle vs. volwasse; 88.67±0.85% totale motiele selle; p <0,001) en morfologiese parameters (onvolwasse; 13.51±0.87% normale kop morfologie vs. volwasse; 20.89±1.20% normale kop morfologie; p <0,001) tussen die twee populasies beduidend verskil. Na 2D-elektroforese is 21 kern proteïen kolle geïdentifiseer wat betekenisvol uitgedruk was tussen onvolwasse en volwasse spermpopulasies. 95% van die nukluêre proteïene wat beduidend verskil het, was minder uitgedruk in die onvolwasse spermpopulasie ten opsigte van die volwasse spermpopulasie. Slegs een kern proteïen naamlik 78kDa Glukose gereguleerde proteïen was meer uitgedruk in die onvolwasse spermpopulasie in vergelyking met die volwasse spermpopulasie. Funksies is toegeskryf aan hierdie proteïene wat direk verband hou met sperm motiliteit, morfologie en energie metabolisme. Ten slotte, in die huidige studie is unieke tegnieke geïmplementeer om proteïen verskille tussen onvolwasse en volwasse spermpopulasies te ondersoek. Uit hierdie resultate is dit duidelik dat proteïen uitdrukking in die totale sperm proteoom en in die kern proteïen fraksie beduidend verskil en onvolledig is in die onvolwasse spermpopulasie ten opsigte van die volwasse spermpopulasie. Op grond van hierdie bevindinge word aanbeveel dat verdere studies op menslike sperme gedoen moet word ten einde die rol van individuele proteïene in sperm funksie te kan bepaal. Proteomika is ‘n ideale tegniek om die iodiopatiese oorsake van manlike infertiliteit te identifiseer, aangesien dit kan help in die identifisering van unieke reseptore (en seintransduksie paaie) wat gebruik kan word om sperm disfunksie te verbeter deur farmaseutiese behandeling.

Airway hyperresponsivness (AHR) is one of most prominent pathophysiological features of asthma. Increasing evidence suggests that vagal bronchopulmonary afferents may be involved in the development of AHR. However, the underlying mechanisms are not clear. Therefore, the purpose of this dissertation was to investigate the effect of chronic airway inflammation induced by allergen sensitization on vagal bronchopulmonary afferents. The study was carried out in an animal model of allergic asthma. Brown-Norway rats were sensitized by intraperitoneal Ovalbumin (Ova) and exposed to aerosolized Ova 3 times/week for three weeks. Control rats received the vehicle. In vivo single-fiber recording technique was applied in this study. Our results showed that chronic Ova exposure caused an elevated baseline activity of pulmonary Cfibers, and a distinctly higher sensitivity of these afferents to chemical stimulants and lung inflation. After an acute Ova inhalation challenge, the increase in baseline activity and the excitability of pulmonary C-fibers were further augmented in sensitized rats, but not in control rats. In addition, sensitivity of pulmonary myelinated afferents to capsaicin was significantly elevated after chronic airway inflammation was induced by allergen. Furthermore, immunohistochemsitry data showed that, in nodose ganglia the proportion of transient receptor potential vanilloids type 1 channels (TRPV1)-expressing bronchopulmonary neurons was significantly higher in sensitized rats than in controls. This increase of TRPV1 expression was found mainly in neurofilament-positive neurons (myelinated neurons), but this effect was absent in jugular ganglia. In conclusion, allergen-induced airway inflammation caused a pronounced sensitizing effect on vagal pulmonary non-myelinated (C-fiber) afferents and elevated the sensitivity of vagal pulmonary myelinated afferents to capsaicin. The latter was accompanied by the upregulation of TRPV1 expression in these myelinated neurons.

Low density lipoprotein receptor (LDLR) is an apolipoprotein E (apoE) receptor and may play a role in Alzheimer’s disease (AD) development. A single nucleotide polymorphism (SNP), rs688, that has been identified to modulate the splicing efficiency of LDLR exon 12 and is associated with higher cholesterol and AD in some case-control populations. The exon 12 deleted mRNA is predicted to produce a soluble form of LDLR that fails to mediate apoE uptake. To gain additional insights, in this study, I seek to understand the regulation of LDLR splicing efficiency. To identify functional cis-elements within LDLR exon 12, I mutated several conserved putative exonic splicing enhancers (ESEs) to neutralize their affinity to serine/arginine-rich (SR) proteins. Transfection of wild type (WT) or mutant LDLR minigenes in HepG2 cells was performed, and splicing efficiency evaluated by quantitative RT-PCR. The results showed that two functional ESEs within exon 12, near rs688, are critical to LDLR splicing. To identify splicing factors that modulate exon 12 splicing, I co-transfected an LDLR minigene and vectors encoding different SR proteins and heterogeneous nuclear ribonucleoproteins (hnRNPs). After quantifying the splicing efficiency, I found that SRp20 and SRp38 increased exon 11- skipping. Moreover, ectopic expression of SRp38-2 and hnRNP G increased exon 11&12-skipping. Interestingly, the actions of hnRNP G did not require its RNA recognition motif (RRM). To further investigate the role of theses splicing factors on LDLR splicing, I quantified the expression level of these splicing factors as well as LDLR splicing efficiency in human brain and liver. I found that SRp38 mRNA expression is associated with LDLR splicing efficiency. In conclusion, this study discovered that rs688 is located close to the two functional ESEs within LDLR exon 12, and revealed a role of SRp38 in LDLR splicing efficiency.

Dysregulation of dopaminergic homeostasis has been established as the primary source of numerous neurological disorders including Parkinson’s and drug addiction. A tonic increase of dopamine (DA) in the nucleus accumbens is required for associating everyday events and behaviors with rewards. Yet many addictive exogenous compounds such as amphetamine (AMPH) and cocaine (COC) produce a much greater augmentation of synaptic DA levels that are linked to euphoria and a shift in behavior towards drug seeking. The protein responsible for maintaining extracellular levels of DA is the dopamine transporter (DAT). It is primarily located in the perisynaptic area at terminals of pre-synaptic neurons where its main function is to sequester DA from the extracellular space and to transport it back into the cell, a process that is electrogenic. AMPH and COC directly interact with DAT and alter its ionic currents. Not much is known about the effect of psychostimulant-induced DAT currents on neuronal excitability and neurotransmitter release. We use synthetic chemistry, molecular biology, and biophysics in heterologous expression systems to decipher the actions of drugs of abuse on DAT. Furthermore we demonstrate drug-induced DAT currents can activate Ca2+ channels associated with dopaminergic excitability. Lastly, we focused on investigating drug effects on excitability in a human midbrain dopaminergic cell line. Understanding how psychostimulants interact with DAT to produce the dysfunctional states of the transporter may facilitate the development of unique therapeutic strategies to treat psychostimulant dependence.

Acute kidney injury (AKI) is a major health burden associated with a 50% mortality rate. Of particular concern, the incidence of AKI has increased dramatically over the last decade. Yet, there is a paucity of available treatments to prevent AKI or to reduce the high rate of AKI-associated mortality. A common cause of AKI, especially in hospital settings, is prolonged decreases in renal blood flow (i.e., renal ischemia). Recent studies have demonstrated that activating the cholinergic anti-inflammatory pathway via vagal stimulation can mitigate AKI severity in rodent models of renal ischemia-reperfusion (IR) injury. While vagal stimulation is not a practical approach to prevent AKI in patients due its invasive nature and numerous side effects, recent studies have identified non-neuronal cholinergic cells within the kidney that could be targeted to reduce the severity of AKI. The overarching goal of this project is to examine the potential role of the renal cholinergic system in modulating the severity of and recovery from AKI in transgenic mice expressing green fluorescent protein (GFP) under control of the choline acetyl-transferase (ChAT) promoter, a protein involved in the synthesis of acetylcholine. The objectives of this study were to develop a clinically relevant model of renal IR-induced AKI in mice by identifying the duration of ischemia required for manifestation of the effects of AKI and to determine whether differences in susceptibility to AKI exists between male and female mice. Initially, male mice underwent 20 (n=3), 22 (n=3), or 25 (n=4) minutes of bilateral renal IR under isoflurane anesthesia with body temperature controlled at 37°C. Ischemia was achieved by careful placement of vascular clamps on the renal artery and vein supplying each kidney. The severity of AKI was determined by measuring serum creatinine (SCr) at 3 days post-AKI. Compared to SCr of mice that were 3 days post-sham AKI (SCr = 0.47 mg/dl, n=2), SCr of male mice from all three ischemia time categories was substantially elevated (SCr > 3 mg/dl, n=10). However, mortality associated with 22 and 25 minutes IR was striking (>90%) making studies of long-term AKI effects difficult. In contrast, 20 minutes IR resulted in AKI manifest by elevated SCr (3.43±0.7 mg/dl, n=3), widespread acute tubular necrosis and a clinically relevant mortality rate of 50%. Next, male (n=10) and female (n=5) mice were subjected to 20 minutes of IR. The mortality rate in male mice (n=10) was 50% (n=10) through 7 days post-AKI; however, all female mice survived. Additional studies showed that female mice had lower SCr 3 days post-AKI (0.63±0.1 mg/dl, n=2) with very modest levels of acute tubular necrosis as compared to the higher SCr (1.92±0.1 mg/dl, n=2) and extensive acute tubular necrosis observed in male mice. The differences observed in AKI severity and mortality rates suggest that female mice are protected against AKI as compared to male mice and future studies will explore the potential role of the renal cholinergic system in contributing to these sex differences in AKI.

Several factors may determine the rate. at which exogenous carbohydrate (CHO) is utilised by the human working muscles during prolonged (> 90 min moderate-intensity (63% of peak sustained power output [PPO]) exercise. These include i) the rate of gastric emptying of an ingested fluid, ii) the rate of digestion, absorption and subsequent transport of glucose into the systemic circulation, and iii) the rate of glucose uptake and oxidation by the working muscles. To test the hypothesis that the rate of gastric emptying is the primary factor limiting the rate of CHO delivery to the working muscles during exercise, uniformly labelled ¹⁴carbon (U-¹⁴C) tracer techniques were used in association with conventional gas exchange measurements and post-exercise gastric aspiration to compare the rates of gastric emptying, intestinal CHO delivery and ingested CHO oxidation from 15 g/100 ml solutions of glucose, maltose, a 22 chain-length glucose polymer, and an isocaloric 'soluble' starch preparation. Two groups of six highly-trained male cyclists or triathletes each ingested two of the test drinks which were given as a 400 ml loading bolus immediately before and then as eight 100 ml feedings at 10 min intervals during 90 min of continuous cycling at a work rate of 63% of PPO (~70% of maximal oxygen consumption [VO₂ₘₐₓ]).