The radioactivity contributions of several daughter products of the 235,238 U and 232Th isotope decay chains within geological matrices can be assumed to be in equilibrium due to their age if they have remained undisturbed for an extended period of time. Similarly, one can assume that the isotopic mass proportions are equal to natural isotopic abundance. Current methods used to ascertain activity in these decay chains involve alpha particle spectrometry or ICP-MS, both of which can be laborious and time consuming. In this research, thermal and epithermal neutron activation analysis of small samples of various geological materials is used in order to ascertain activities. Through the use of NAA, cumbersome sample preparation and the need for large sample size and extended counting time are obviated. In addition to the decay chains of uranium and thorium, 40K, another large contributor to naturally occurring radioactivity, is determined using epithermal neutron activation analysis to determine total potassium content, and then calculating its isotopic contribution based on its natural isotopic abundance. / text

My PhD project investigated the regulation of human cardiac transient outward potassium current (Ito) by protein tyrosine kinases (PTKs) and the functional expression of transient receptor potential (TRP) channels in human atrial myocytes to make an advanced understanding of human cardiac electrophysiology and pathophysiology. The modulation of human cardiac Itoby PTKs was studied in human atrial myocytes and HEK 293 cells expressing hKv4.3 (coding human cardiac Ito). We found that the broad-spectrum PTK inhibitor genistein, the selective EGFR kinase inhibitor AG556, and the Src-family kinases inhibitor PP2 inhibited human atrial Itoand the inhibitory effect was countered by the protein tyrosine phosphatase (PTP) inhibitor orthovanadate. Similar results were observed in hKv4.3-HEK cells. Interestingly, tyrosine phosphorylation of hKv4.3channels was reduced by genistein, AG556, and PP2,and the reduction was antagonized by orthovanadate. The mutant Y136F of hKv4.3 lost the inhibitory response to AG556, whileY108F lost the response to PP2.The double mutant Y108F-Y136F hKv4.3 failed to respond to both AG556 and PP2, and exhibited a dramatic reduction of tyrosine phosphorylation. These results indicate that native cardiac Itois regulated by both EGFR and Src family kinases. In the second part, we studied whether TRPC channels would mediate the nonselective cation current described previously in human atrial myocytes. It was found that TRPC1 channel activator thapsigargin activated the current, and the effect was suppressed by La3+or prevented by intracellular anti-TRPC1 antibody. Endothelin-1 and angiotensin II stimulated the current, andthe effect was inhibited by La3+and/or 2-APB. RT-PCR and Western blot analysis revealed that in addition to the TRPC1 channels mediating the nonselective cation current, the components of store-operated Ca2+channels (SOCs), STIM1 and Orai1 were abundantly expressed in human atria. The interaction of TRPC1, STIM1, and Orai1 was confirmed by co-immunoprecipitation. Interestingly, we found that protein expression of TRPC1 and STIM1, but not Orai1, was up-regulated in human atria with atrial fibrillation. The third part of the project determined whether TRPM7 channels were expressed in human atrial myocytes, since this channel was reported in human atrial fibroblasts, conferring atrial fibrosis in human atria with atrial fibrillation. We found a TRPM7 -like current which was potentiated by acidic pH, and inhibited by La3+and 2-APB, and a Ca2+-activated TRPM4 current. RT-PCR and Western blot analysis confirmed the expression of TRPM7 and TRPM4 channels in human atria. Moreover, we found TRPM7 protein, but not TRPM4 protein was significantly up-regulated in human atria with atrial fibrillation, suggesting the potential participation of TRPM7 channels in atrial remodeling of human atria with atrial fibrillation. Collectively, this PhD thesis project has demonstrated for the first time that human cardiac Itois modulated by EGFR kinase and Src kinases via phosphorylating Y136and Y108, respectively. TRPC1 channels mediate the nonselective cation current and SOCs.TRPM7 channels are expressed in human atrial myocytes. The up-regulation of TRPC1, STIM1, and TRPM7 channels in human atria with atrial fibrillation suggest that they are likely involved in atrial electrical and/or structure remodeling in patients with atrial fibrillation. / published_or_final_version / Medicine / Doctoral / Doctor of Philosophy

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Spreading depression (SD) is an interesting and important phenomenon due to its role in mammalian pathologies such as migraine, seizures, and stroke. Until recently investigations of the mechanisms involved in SD have mostly utilized mammalian cortical tissue, however in my thesis I demonstrated that SD-like events occur in the CNS of an invertebrate model, Locusta migratoria. Locusts enter comas in response to stress during which neural and muscular systems shut down until the stress is removed, and this is believed to be an adaptive strategy to survive extreme environmental conditions. Using the ventilatory central pattern generator (vCPG) as a model circuit I was able to show that stress-induced arrest of vCPG function is associated with SD-like events in the locust metathoracic ganglion (MTG) that closely resemble cortical SD (CSD) in many respects, including mechanism of induction, extracellular potassium ion ([K+]o) changes, and propagation in areas equivalent to mammalian grey matter. SD-like events in the locust were characterized as abrupt [K+]o increases associated with electrical activity silence in the locust CNS that propagate to other areas within the MTG. In this thesis I described the generation of comas by several cellular stressors (hyperthermia, metabolic stressors, Na+/K+-ATPase inhibition, and KCl) and the associated SD-like events in the locust, provide a description of the similarities to CSD, and show how they can be manipulated both by stress preconditioning and pharmacologically. I showed that hyperthermic vCPG arrest can be preconditioned by prior heat shock (HS) treatment and induced-thermotolerance was associated with an increased rate of [K+]o clearance associated with vCPG recovery that was not linked to changes in ATP levels or total Na+/K+-ATPase activity. I also provided evidence for the involvement of the stress-sensor AMP-activated protein kinase (AMPK) in stress-induced comas in the locust. AMPK activation was linked to a switch in motor pattern behavior following recovery from anoxia-induced vCPG arrest and exacerbated repetitive SD-like events induced by ouabain (Na+/K+-ATPase inhibitor). I suggested that locust SD-like events are adaptive by conserving energy and preventing cellular damage, and I provided a model for the mechanism of SD onset and recovery in the locust nervous system. / Thesis (Ph.D, Biology) -- Queen's University, 2010-08-05 16:08:19.905

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