Malpighian tubules of A. dorsalis mosquito larvae, studied in vitro, actively transported magnesium at high rates against concentration gradients as large as 16-fold and transepithelial potential gradients of approximately -l5mV. Fluid secretion rates, determined over 90 minute periods, in the presence and absence of cAMP, indicated that A. dorsalis tubules were viable and had secretion rates of the same magnitude as those reported for A. taeniorhynchus tubules. Having characterized the in vitro preparation of Malpighian tubules, the main hypothesis that Mg²⁺ transport is driven predominately by counter transport with Na⁺ was tested. This hypothesis was not supported by kinetic, Na-substitution, or inhibitor studies. Kinetic and Bumetanide studies suggest backflux of K drives J mg; however, this was not consistently found in other studies. / Science, Faculty of / Zoology, Department of / Graduate

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