Thesis (Ph. D.)--Illinois State University, 1997. / Title from title page screen, viewed June 13, 2006. Dissertation Committee: Radheshyam K. Jayaswal (chair), Brian J. Wilkinson, Mathew J. Nadakavukaren, Herman E. Brockman, Alan J. Katz. Includes bibliographical references and abstract. Also available in print.

Universiẗat, Diss., 2003--Münster (Westfalen).

Thesis (M. Sc.)--Brock University, 2006. / Includes bibliographical references.

Techn. Universiẗat, Diss., 2004--Dresden.

Universiẗat, Diss., 2004--Münster (Westfalen).

Thesis (M.S.)--Brock University, 2006. / Includes bibliographical references (leaves 88-111). Also available online (PDF file) by a subscription to the set or by purchasing the individual file.

The effect of temperature on the gill morphology and ion transporter distribution in the branchial epithelium of a freshwater teleost, the Koi carp (Cyprinus carpio, L.) was examined. Three different water temperatures were used to detect changes in expression level of transporter proteins in the gill epithelial cells. With increasing temperature, the expression level of all three ion transporters studied declined, and the gill lamellae protruded out of the cell mass, thus increasing the surface area of the branchial epithelium. A hypothetical organization of the transporter proteins within the ionocytes is proposed.

Zebrafish, Danio rerio, are able to survive exposure to extreme acidity (pH 4). Because previous studies demonstrated that disruption of ionic balance during exposure to acidic water is the major cause of mortality in acid-sensitive freshwater species, the focus of this thesis was to characterize the molecular mechanisms enabling zebrafish to maintain their Na+ homeostasis following exposure to acidic water. Initial findings (Chapter 2) demonstrated that branchial mRNA expression of selected isoforms of claudins, major components of tight junctions, are altered in an isoform-dependent manner, suggesting the potential regulation of epithelial permeability to minimize ion loss. Concurrently, a marked stimulation of Na+ uptake was observed in adults and larvae following acid-exposure. Because of the uniqueness of this response (increasing Na+ uptake in acidic water) among freshwater teleosts, the mechanisms related to Na+ uptake and its stimulation were investigated further (Chapters 3 - 7). Pharmacological treatments and gene knockdown approaches revealed that a functional metabolon consisting of an apically expressed Na+-H+-exchanger (NHE3b) in association with an apically expressed ammonia-conducting channel (Rhcg1), enables Na+ uptake in acidic water. During chronic (>1 day) exposure to acidic water, cortisol (via glucocorticoid receptors) and catecholamines (via β-adrenergic receptors) are involved in stimulating Na+ uptake. Although catecholamines may act on both NHE3b and Na+-Cl- co-transporter (NCC), the effects of cortisol on Na+ uptake are mediated primarily by activation of NHE3b. On the other hand, during acute (<3 h) exposure to acidic water, cortisol does not appear to affect Na+ uptake; rather, the stimulation of Na+ uptake appears to be mediated by angiotensin II and catecholamines. Cyclic AMP (cAMP), a signalling molecule synthesized following the activation of β-adrenergic receptors, is critically involved in stimulating Na+ uptake, likely via activation of NHE3b and NCC. In agreement with this idea, ionocytes that express NHE3b also express high levels of β-adrenergic receptor (propranolol binding sites) as well as trans-membrane adenylyl cyclase (forskolin binding sites). Taken together, the results of this thesis provide fresh insight into the mechanisms of osmoregulation in freshwater (FW) fish. In particular, the data reveal the presence of complex pathways regulating Na+ uptake in zebrafish exposed to acidic water. The relative importance of the various pathways depends in part on the duration of exposure; acute versus chronic.

Fetal programming results from stressors during fetal development and may influence the occurrence of disease later in life. Maternal nutritional status and/or environment can affect renal development by inducing limited nephron endowment at birth, which results in diseases such as hypertension and coronary heart disease in mammals. Birds are likely to be effective models for this process because, like mammals, they have high pressure cardiovascular systems, mammalian-type nephrons and are homeothermic. This project uses the chicken embryo to explore physiological responses of disrupted hydration state thereby providing insights into renal fetal programming. Under normal conditions the chorioallantoic membrane (CAM) and developing avian kidney work in unison to ensure a proper balance of ions and water within the egg. White leghorn chicken eggs were incubated at 37.5oC±0.5oC and either <35%, 55-60% (normal) or >85% relative humidity. Amniotic fluid serves as the drinking source for the embryo late in development; its composition is important to salt and water homeostasis. High amniotic fluid osmolality increased the blood osmolality for embryos exposed to low humidity incubation thereby indirectly influencing the renal developmental program of the embryos from this group. Indeed estimated filtering capacity was doubled in the low humidity group (6.77 ± 0.43 mm3) compared to normal (4.80 ± 0.33 mm3) and high (3.97 ± 0.30 mm3) humidity groups. The increased filtering capacity seen for those embryos from low humidity may indicate the ability for more efficient recovery of water if similarly stressed as an adult bird. All embryo populations maintained similar oxygen consumption (0.075 ml/min - 0.37 ml/min), hematocrit (15 % - 32 %) and hemoglobin values (4 g/dl - 9 g/dl), thus displaying control over these aspects of the internal environment despite the obvious environmental insult of extreme incubation humidity. These results signify the embryo's immature kidney, along with lower gastrointestinal tract, functions much like the adult form maintaining homeostasis, although the mechanisms may differ. The overall benefits of this research included better understanding of the role the kidney during embryonic development and determining whether environmental factors, such as humidity, leave an imprint on morphological and physiological aspects of the urinary system of the embryo and water compartments of the egg.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23040号 / 理博第4717号 / 新制||理||1676(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)准教授 渡辺 勝敏, 教授 曽田 貞滋, 教授 沼田 英治 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM