Calcium (Ca2+) is a universal second messenger controlling a wide variety of cellular reactions and adaptive responses. All the versatility of a Ca2+ signaling requires that the concentration of Ca2+ ions in the cytoplasm be highly regulated. Generation of Ca2+ mobilizing signals in cells involves regulation by multiple components controlling Ca2+ release from the internal stores, Ca2+ influx across the plasma membrane, elicitation of Ca2+ sensitive processes and finally the removal of Ca2+ from the cells. Inositol-1, 4, 5-trisphosphate receptors (IP3Rs) and ryandine receptors (RyRs) are the most studied Ca2+ release channels located on the internal stores. Previous studies have shown ryanodine receptors (RyRs) play a key role in the process of Ca2+ signaling participating in the oscillatory patterns of controlling the release of Ca2+ from ER and regulating the influx of Ca2+ by coupling with plasma Ca2+ channels. Although recent progress deciphered the behavior and function of RyRs in regulation of Ca2+ signal, it still remains mysterious in understanding the molecular mechanism of its regulation and its connection with plasma membrane Ca2+ channels in neuronal cells. Here this study aimed to utilized the most cutting-edge RNA interference techniques, along with well-characterized pharmacological regulators of RyRs, to better characterized the role of RyRs is our neuronal cell line model NG115-401L. Our first main goal of this project was to develop an effective protocol that could selectively knockout or knockdown expression levels of the RyR1 gene in NG115-401L cells. After testing different siRNA primers including their combination with different transfection reagent, the result shows a significant silencing effect to the RyR1 mRNA expression levels. In the second part of this study, we used a group of pharmacological agents with well-known regulatory actions on RyRs to characterize the functional roles of the RyRs expressed in NG115-401L cells. All four agonists which are ryanodine, caffeine, CMC and PCB 95 show their abilities to activate the RyRs, increase [Ca2+]iand induce the influx of Ca2+ via SOC. After transfected NG115-401L cells by siRNA, the Ca2+ release and influx signals were highly diminished suggesting RyR1 gene was successfully knocked down and the successfully knocked down and the Ca2+ mobilization mediated by RyR1 was decreased greatly. Finally in order to study the effects of the regulation of Ca2+ by RyR modulators and RyR gene knockdown on cell growth patterns and cell viability, the NG115-401L cells were exposed to various concentrations of RyR regulators and siRyR1 primer for different time periods. The siRNA transfection showed the least effect on cell growth, as compared with pharmacological agents that modulate RyR function. Considering we achieved high levels of gene knockdown and its low cytotoxity, our result suggests that siRNA silencing for RyRs may become a promising gene therapeutic target in the future.

A 3- to 5-fold increase in Ca2+ accompanies cataract formation induced by selenite. The mechanism of selenite cataractogenesis involves calcium activation of calpain with subsequent proteolysis within the lens nucleus. This study was undertaken to investigate the biochemical mechanisms that lead to calcium accumulation in these circumstances. The components responsible for rat lens calcium regulation were defined by using either lens membrane vesicle preparations or intact lenses. Both Na+ gradient-dependent Ca2+ uptake and efflux occurred in lens membrane vesicles. Experiments with intact lenses showed that Na + ICa2 + exchange plays an important role in lens calcium regulation. ATP-dependent Ca2+ uptake and Ca2+ -dependent ATP hydrolytic activity have been characterized in lens membrane vesicles. Therefore, both Ca2+ -ATPase and Na + ICa2+ exchange participate in rat lens calcium regulation. Calcium accumulation in lenses treated by selenite may result from either increased influx (via non-selective cation channel), decreased efflux (via Ca2 +-ATPase and Na+ ICa 2+ exchange) or both. The selenite effects on the different components involved in lens calcium regulation were tested. / Ph. D.

No description available.

The initiation of lactation involves an increased flow of Ca into mammary secretions, which leads to responses of serum concentrations of Ca and parathyroid hormone (PTH) that may be influenced by dietary Ca. Eight light mares from Farm A and eight Thoroughbred mares from Farm B were bled and milked 10 d pre-foaling, and eight mares (four from each farm) were bled and milked 5 d post-foaling. Milk Ca was measured by two commercial tests, one for [Ca + Mg] and the other [Ca]. Serum PTH and total Ca were measured in 16 mares, and ionized Ca in four mares. Parturition was induced in all mares with fenoprostalene on Farm A, and in four mares with oxytocin on Farm B; no significant difference was found between induction methods or between induced and spontaneous foaling mares. Dietary Ca was 34% DM on Farm A and .79% on Farm B. Mean serum total Ca concentrations decreased from 12.5 mg/dl to a nadir of 11 mg/dl on d 2 post-partum, and mean PTH increased from 46 pg/ml to a peak of 186 pg/ml on d 2 post-partum. Mean serum PTH concentrations were lower (P = .03) and total Ca concentrations were higher (P = -01) on Farm B in comparison to Farm A, probably reflecting the difference in Ca intake. The nadir in mean ionized Ca and total Ca concentrations was reached on d 2 post-partum, 1 day later than has been observed previously in the dairy cow. Milk Ca concentrations increased from 50 ppm 7 d pre-foaling to 350 ppm on the day of foaling, with no difference between farms. The [Ca + Mg] test reached a critical level of 200 ppm 4.5 d pre-foaling, the [Ca] test 2 d pre-foaling. The [Ca + Mg] and [Ca] tests reached 250 ppm 2.5 and 1 d pre-partum, respectively. In short, serum Ca and PTH concentrations showed periparturient changes which reflected dietary Ca pre-partum. Foaling date was more closely associated with milk [Ca] than with [Ca + Mg] and by a critical level of 250 ppm than by 200 ppm. / Master of Science

Organophosphorus compounds are widely used in agriculture as pesticides and in industry as petroleum additives and modifiers of plastics. Some of these compounds are capable of inducing an irreversible neuropathy developing weeks to months after exposure, yet there is no effective treatment. This may be due in part to the lack of knowledge of how this neuropathy develops. In this dissertation, it is proposed that as a consequence of a triggering event, peripheral nerves may be predisposed to an increase in calcium (Ca⁺⁺) mobilization and the neuronal accumulation of this cation. This increase in Ca could thereby initiate a cascade of events, in both nerve and muscle, that may account for some of the detrimental changes occurring during organophosphorus-induced delayed neuropathy (OPIDN). The involvement of Ca⁺⁺ in the pathogenesis of OPIDN was tested using functional, morphological, and biochemical techniques in the domestic hen, the recognized animal model of OPIDN. The isolated biventer cervicis nerve-muscle preparation was developed for quick assessment of the time course of OPIDN deficits and validated by comparison to in vivo preparations. This preparation proved more sensitive by functional and morphological evaluation indicating early damage at 4 days following exposure and before appearance of clinical signs. Regeneration was detected after 21 days. OPIDN was modified by using Ca⁺⁺ channel blockers, nifedipine, and verapamil, in the presence of phenyl saligenin phosphate, an active neurotoxicant. Attenuation of OPIDN by these compounds was revealed by clinical assessment, by changes in nerve excitability denoted by strength-duration relationships in response to electrical stimulation, by denervation hypersensitivity to neurotransmitter, and by morphology. These modifiers attenuated all degenerative responses. Furthermore, it was revealed that the activity of Ca⁺⁺-activated neutral protease (CANP), an enzyme responsible for neurofilament degradation, was increased in OPIDN. Such increases were ameliorated by modifiers of Ca movement. This study strongly suggests that Ca⁺⁺, possibly through activation of CANP, may contribute to functional and morphological deficits of OPIDN. / Ph. D.

Ma, Ka Ying. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 113-129). / Abstracts in English and Chinese. / ACKNOWLEDGMENTS --- p.I / ABSTRACT --- p.II / LIST OF ABBREVIATIONS --- p.VII / TABLE OF CONTENTS --- p.IX / Chapter Chapter 1 --- General Introduction --- p.1 / Chapter 1.1 --- Calcium --- p.1 / Chapter 1.1.1 --- Recommendation of calcium intake --- p.1 / Chapter 1.1.2 --- Calcium toxicity --- p.2 / Chapter 1.1.3 --- Calcium homeostasis --- p.2 / Chapter 1.1.3.1 --- Role of parathyroid hormone in calcium homeostasis --- p.4 / Chapter 1.1.3.2 --- "Role of 1,25-dihydroxyvitamin D3 in calcium homeostasis" --- p.4 / Chapter 1.1.3.3 --- Role of calcitonin in calcium homeostasis --- p.6 / Chapter 1.2 --- Magnesium --- p.7 / Chapter 1.2.1 --- Recommendation of magnesium intake --- p.7 / Chapter 1.2.2 --- Absorption and secretion of magnesium --- p.8 / Chapter 1.3 --- Cholesterol --- p.9 / Chapter 1.3.1 --- Cholesterol homeostasis --- p.11 / Chapter 1.3.1.1 --- Role of LDLR --- p.14 / Chapter 1.3.1.2 --- Role of SREBP-2 --- p.17 / Chapter 1.3.1.3 --- HMGR as rate limiting step for cholesterol synthesis --- p.19 / Chapter 1.3.1.4 --- CYP7A1 as a key factor in production of bile acids --- p.21 / Chapter 1.3.1.5 --- Role of LXR in production of bile acids --- p.22 / Chapter 1.3.1.6 --- AC AT regulates cholesterol uptake in intestine --- p.22 / Chapter Chapter 2 --- Effect of Calcium Deficiency and Inadequacy on Blood Cholesterol Level in Intact Male and Castrated Hamsters --- p.25 / Chapter 2.1 --- Introduction --- p.25 / Chapter 2.2 --- Objective --- p.28 / Chapter 2.3 --- Materials and methods --- p.29 / Chapter 2.3.1 --- Hamsters --- p.29 / Chapter 2.3.1.1 --- Intact male hamster --- p.29 / Chapter 2.3.1.2 --- Castrated hamster --- p.30 / Chapter 2.3.2 --- Diets --- p.31 / Chapter 2.3.3 --- Determination of calcium content in animal diet --- p.33 / Chapter 2.3.4 --- "Determination of serum lipid, lipoproteins and calcium concentration" --- p.33 / Chapter 2.3.5 --- Determination of cholesterol concentration in organs --- p.34 / Chapter 2.3.6 --- Determination of fecal neutral and acidic sterols --- p.37 / Chapter 2.3.7 --- Determination of fecal neutral sterols --- p.37 / Chapter 2.3.8 --- Determination of fecal acidic sterols --- p.40 / Chapter 2.3.9 --- Statistics --- p.42 / Chapter 2.4 --- Results on intact male hamsters --- p.43 / Chapter 2.4.1 --- Diet composition --- p.43 / Chapter 2.4.2 --- Growth and food intake --- p.43 / Chapter 2.4.3 --- Organ weights --- p.43 / Chapter 2.4.4 --- Effect of calcium deficiency diet on the plasma lipid profile and calcium concentration of hamsters --- p.43 / Chapter 2.4.5 --- Effect of calcium deficiency diet on hepatic cholesterol of hamsters --- p.44 / Chapter 2.4.6 --- Effect of calcium on fecal neutral sterol output --- p.48 / Chapter 2.4.7 --- Effect of calcium on fecal acidic sterol output --- p.48 / Chapter 2.5 --- Results on castrated hamsters --- p.50 / Chapter 2.5.1 --- Growth and food intake --- p.50 / Chapter 2.5.2 --- Organ weights --- p.50 / Chapter 2.5.3 --- Effect of calcium deficiency diet on the plasma lipid profile and calcium concentration of hamsters --- p.50 / Chapter 2.5.4 --- Hepatic cholesterol --- p.50 / Chapter 2.5.5 --- Effect of calcium on fecal neutral sterol output --- p.53 / Chapter 2.5.6 --- Effect of calcium on fecal acidic sterol output --- p.53 / Chapter 2.6 --- Discussion --- p.55 / Chapter Chapter 3 --- Effect of Calcium Deficiency and Inadequacy on Blood Cholesterol Level in Intact Female and Ovariectomized Hamsters --- p.57 / Chapter 3.1 --- Introduction --- p.57 / Chapter 3.2 --- Objective --- p.58 / Chapter 3.3 --- Materials and methods --- p.59 / Chapter 3.3.1 --- Hamsters --- p.59 / Chapter 3.3.1.1 --- Intact female hamster --- p.59 / Chapter 3.3.1.2 --- Ovariectomized hamster --- p.60 / Chapter 3.3.2 --- Diets --- p.60 / Chapter 3.3.3 --- "Determination of serum lipid, lipoproteins and calcium concentration" --- p.60 / Chapter 3.3.4 --- "Determination of cholesterol concentration in organs, fecal neutral and acidic sterols" --- p.60 / Chapter 3.3.5 --- "Western blottting of liver SREBP-2, LDLR, HMGR, LXR and CYP7A1 proteins" --- p.61 / Chapter 3.3.6 --- Preparation of intestinal microsome --- p.62 / Chapter 3.3.7 --- Intestinal acyl coenzyme A: cholesterol acyltransferase (ACAT) activity measurement --- p.63 / Chapter 3.3.8 --- Statistics --- p.64 / Chapter 3.4 --- Results on intact female hamsters --- p.65 / Chapter 3.4.1 --- Growth and food intake --- p.65 / Chapter 3.4.2 --- Organ weights --- p.65 / Chapter 3.4.3 --- Effect of calcium deficiency diet on the plasma lipid profile and calcium concentration of hamsters --- p.65 / Chapter 3.4.4 --- Effect of calcium deficiency diet on hepatic cholesterol of hamsters --- p.65 / Chapter 3.4.5 --- Effect of dietary calcium on fecal neutral sterol output --- p.66 / Chapter 3.4.6 --- Effect of dietary calcium on fecal acidic sterol output --- p.66 / Chapter 3.4.7 --- Effect of dietary calcium on liver LDLR immunoreactive mass --- p.71 / Chapter 3.4.8 --- Effect of dietary calcium on liver CYP7A1 immunoreactive mass --- p.71 / Chapter 3.4.9 --- Effect of dietary calcium on liver LXR immunoreactive mass --- p.71 / Chapter 3.4.10 --- Effect of dietary calcium on liver SREBP-2 immunoreactive mass --- p.71 / Chapter 3.4.11 --- Effect of dietary calcium on liver HMGR immunoreactive mass --- p.71 / Chapter 3.4.12 --- Effect of dietary calcium deficiency on intestinal ACAT activity --- p.77 / Chapter 3.5 --- Results on ovariectomized hamsters --- p.79 / Chapter 3.5.1 --- Growth and food intake --- p.79 / Chapter 3.5.2 --- Organ weights --- p.79 / Chapter 3.5.3 --- Effect of calcium deficiency diet on plasma lipid profile and calcium concentration of hamsters --- p.79 / Chapter 3.5.4 --- Hepatic cholesterol --- p.79 / Chapter 3.5.5 --- Effect of dietary calcium on fecal neutral sterol output --- p.80 / Chapter 3.5.6 --- Effect of dietary calcium on fecal acidic sterol output --- p.80 / Chapter 3.5.7 --- Effect of dietary calcium on liver LDLR immunoreactive mass --- p.85 / Chapter 3.5.8 --- Effect of dietary calcium on liver CYP7A1 immunoreactive mass --- p.85 / Chapter 3.5.9 --- Effect of dietary calcium on liver LXR immunoreactive mass --- p.85 / Chapter 3.5.10 --- Effect of dietary calcium on liver SREBP-2 immunoreactive mass --- p.85 / Chapter 3.5.11 --- Effect of dietary calcium on liver HMGR immunoreactive mass … --- p.85 / Chapter 3.6 --- Discussion --- p.91 / Chapter Chapter 4 --- Effect of Dietary Magnesium Supplementation on Blood Cholesterol Level in Intact Male Hamsters --- p.94 / Chapter 4.1 --- Introduction --- p.94 / Chapter 4.2 --- Objective --- p.96 / Chapter 4.3 --- Materials and methods --- p.97 / Chapter 4.3.1 --- Hamsters --- p.97 / Chapter 4.3.2 --- Diets --- p.98 / Chapter 4.3.3 --- "Determination of serum lipid, lipoproteins and magnesium concentration" --- p.100 / Chapter 4.3.4 --- "Determination of cholesterol concentration in organ, fecal neutral and acidic sterols" --- p.100 / Chapter 4.3.5 --- Statistics --- p.100 / Chapter 4.4 --- Results on male hamster --- p.101 / Chapter 4.4.1 --- Growth and food intake --- p.101 / Chapter 4.4.2 --- Organ weights --- p.101 / Chapter 4.4.3 --- Effect of dietary magnesium on plasma lipid profile and magnesium concentration in hamsters --- p.101 / Chapter 4.4.4 --- Effect of dietary magnesium on hepatic cholesterol of hamsters..… --- p.102 / Chapter 4.4.5 --- Effect of dietary magnesium on fecal neutral sterol output --- p.105 / Chapter 4.4.6 --- Effect of dietary magnesium on fecal acidic sterol output --- p.105 / Chapter 4.6 --- Discussion --- p.107 / Chapter Chapter 5 --- Conclusion --- p.110 / References --- p.113

Neuronal connections in cat visual cortex are highly susceptible to visual experience at early postnatal age and thus serve as a useful model of neural plasticity. The biochemical mechanisms underlying this cortical plasticity remain unclear. In this thesis, the development of several elements in calcium-related signal transduction systems, including the type-1 muscarinic and alpha-1 adrenoceptor systems as examples of cell surface receptors and protein kinase C. calcium/calmodulin dependent kinase II and inositol 1,4,5 phosphotate receptors as second messenger targets, were investigated using the methods of immunocytochemistry and autoradiography. The results show that each receptor develops with its own time-table and laminar distribution; the various elements all culminate and display the maximal colocalization during the critical period; and, only at this age, the cortical levels of the receptors and kinases are dependent on subcortical afferents. The results suggest that cell surface receptors and their second messenger targets develop in specific temporal and spatial patterns, which may be both genetically and environmentally determined, and this specific sequence of development of the molecules for signal transduction results in a series of modifications in the morphology and physiology of the developing cortex leading to its maturation. / Medicine, Faculty of / Graduate

Calcium (Ca2+) plays an important role as a second messenger, transmitting the message of arrival of stimuli such as hormones and neurotransmitters to the intracellular system that carries out the cellular response to the stimulus. The universality of Ca2+ as an intracellular messenger depends on its enormous versatility. This versatility is exploited to control processes as diverse as fertilization, proliferation, development, learning and memory, contraction and secretion, and must be accomplished within the context of Ca2+ being highly toxic. Ryanodine receptors (RyRs) and inositol trisphosphate receptors (IP3Rs) are Ca2+ -release channels located on intracellular membranes of the endoplasmic reticulum (ER)/sarcoplasmic reticulum (SR) that perform essential functions as key targets of hormone/neurotransmitter action to initiate intracellular Ca2+ signals. The purpose of this project was to study the role of RyR2 in Ca2+ signaling in the NG115-401L neuronal cell line. siRNA transfection methods were employed to knockdown RyR2 expression levels in NG115-401L cells. We used reverse transcription and real-time PCR to evaluate RyR2 gene expression in transfected/untransfected cells. We also evaluated cytosolic Ca2+ changes induced by RyR activators or regulators, using fura-2 AM as the Ca2+ indicator. Successful RyR2 gene knockdown allowed us to carry out some initial experiments to characterize the specific roles played by the RyR2 receptor isoform. We examined cell responses to FK-506 under the condition of RyR2 knockdown, finding that RyR2 appears to confer selectivity to this response. Finally, the effects of siRNA transfection and FK-506 treatment on NG115-401L cell growth were evaluated. These experimental results may contribute to future studies of RyR2, and help develop novel treatments for RyR2-base d dysfunctional diseases.

We investigated the relationship between calcium and protein intake and bone loss over a one-year period in 99 early postmenopausal women (1-36 months) aged 51.3 �� 0.31 years. Bone mineral density (g/cm��) of the left hip (total hip, femoral neck, greater trochanter) and lumbar spine (L1-L4) as well as body composition were assessed using dual energy x-ray absorptiometry. Dietary intake of calcium and protein was assessed using a 100-item Block Food Frequency Questionnaire. A physical activity questionnaire was also completed by the subjects to estimate energy expenditure. Paired t-tests revealed that there were no significant differences between baseline and month 12 physical characteristics except for percent fat which increased from 31.99 �� 0.60% to 32.44 �� 0.61% (p=.009). At month 12, bone mineral density decreased significantly at the femoral neck (-0.97 �� 0.31%) and total hip (-0.55 �� 0.24%). The average calcium, protein and calcium to protein ratio intake for the group was 1129.88 �� 46.22mg/day, 57.88 �� 1.93g/day and 20.10 �� 0.71m/g, respectively. Partial correlation analyses showed no significant relationships between change in bone mineral density and average intakes for calcium, protein, or the calcium to protein ratio. After adjusting for hormone replacement status, lean body mass and months post menopause, analysis of covariance revealed that there were no significant differences between groups when intakes of calcium, protein and the calcium to protein ratio were separated into "above recommended" and "below recommended" categories (above or below 1000/1500mg/day, 50g/day, 20:1 mg/g/day, respectively). Our results suggest that consuming adequate amounts of calcium and protein does not appear to significantly slow bone loss after 12 months in early postmenopausal women. / Graduation date: 2003

The versatility of Ca2+ as a messenger regulating a myriad of signalling events requires that the concentration of Ca2+ ions in the cytoplasm be highly regulated. Capacitative Ca2+ entry (CCE) or store-operated Ca2+ (SOC) entry, whereby the depletion of intracellular Ca2+ stores induces the influx of Ca2+ across the plasma membrane, plays a crucial role in Ca2+ signalling. Despite the recent advances in elucidating the entry pathway, its molecular identity, biophysical properties and store-depletion signal remains undefined. Thapsigargin (TG), a sarcoplasmic/endoplasmic reticulum Ca2+ A TPase pump (SERCA), inhibitor induces passive depletion of the internal Ca2+ stores and triggers CCE. The universality of this signal has been widely accepted and TG has proven to be a valuable tool in studying CCE. The neuronal cell line NG 115 -401 L lacks the TG activated Ca2+ influx pathway. Agonists of the ryanodine receptor (RyR); chlorom- cresol (CMC), polychlorinated biphenyl 95 (PCB), ryanodine, caffeine, and that of the inositol-1 ,4 ,5-trisphosphate receptor (IP3R), bradykinin, effectively couple to the activation of Ca2+ influx in these cells. The Ca2+ influx signal due to these agonists can be inhibited by SOC blockers such as La3+, Zn2+, Ni2+ and SF&F 96365. Thapsigargin, CMC and PCB95 share the same Ca2+ releasable pools in the 401 L cells. Our data thus suggests that the channels present in the 401 L cells are likely to be receptor-activated channels rather than the store-depletion activated channels. Cell viability studies show that thapsigargin (25 nM) can decrease viability by 75% within 24 hrs and the RyR agonist caffeine decreased viability to <60% within 24hrs. CMC, PCB95 and ryanodine also were cytotoxic at higher doses. Nuclear fragmentation patterns and activation of caspase-3 in thapsigargin and caffeine-treated cells suggest the induction of apoptosis within 12 hrs of treatment. The treated cells were shown to generate nitric oxide, a potential apoptosis inducing agent.