Mutagenic heterocyclic amines are produced during the ordinary cooking of meats and fish. When metabolically activated, heterocyclic amines will form covalent adducts with DNA, which, if not repaired, may affect the flow of genetic information in a cell. It has been proposed previously that heterocyclic amine mutagens contribute to the incidence of dietary-related cancers because they cause somatic cell mutations and induce tumors in rodents and nonhuman primates. Recent work has shown that some cooked food mutagens preferentially produce DNA damage in heart cells, DNA adduct levels are directly related to dose and duration of mutagen exposure, the dietary damage persists for long intervals in cardiac tissue, and mitochondrial DNA is more vulnerable than nuclear DNA to these mutagens. Because cardiac myocytes are terminally differentiated cells that have lost their ability to divide, the capacity to repair DNA damage is a critical factor in the proper function of cardiomyocytes, and cardiac myocytes seem to have limited DNA repair capabilities. DNA damage formed by dietary components, such as heterocyclic amines, might accumulate with time because of inefficient repair and thereby affect heart cell function or viability. The possibility that dietary habits play a role in idiopathic cardiomyopathies and congestive heart disease should be explored in greater depth.

No description available.

O aumento da pressão arterial não é a única consequência da sobrecarga de sal na dieta. Independente dos efeitos hemodinâmicos, o excesso de sal pode induzir alterações estruturais no miocárdio. A avaliação dos mecanismos destas alterações foi o objetivo do presente estudo. Para tanto, ratos Wistar machos foram alimentados com dieta: normossódica (NR: 1,3% de NaCl), hipersódica 1 (HR1: 4%) e hipersódica 2 (HR2: 8%) desde o desmame até a 18a semana de idade. O grupo HR2 foi dividido em HR2, HR2+Hidralazina (HZ: 15mg/ kg/ dia) e HR2+Losartan (LOS: 20mg/ kg/ dia). As drogas foram administradas a partir da 7a semana de idade. Foram avaliados pressão arterial caudal (PAc), atividade de renina plasmática (ARP), aldosterona sérica, ecocardiograma, massa ventricular esquerda (MVE) e direita (MVD), medida do diâmetro transverso do miócito (DTM), fibrose intersticial (FI), expressão protéica do receptor de angiotensina II do tipo I (AT1) e tipo 2 (AT2), dosagem de angiotensina II (AII) e ligação do anticorpo que reconhece a conformação ativada dos receptores AT1 e AT2 no ventrículo esquerdo (VE) e direito (VD). A PAc foi maior no grupo HR1 e HR2 comparado com o grupo NR. A PAc do grupo HR2+HZ e HR2+LOS não diferiu do grupo NR. ARP e ALDO foram menores nos grupos HR1, HR2, HR2+HZ e HR2+LOS. A espessura do septo interventricular na diástole e da parede posterior do ventrículo esquerdo na diástole foram maiores nos grupos HR1, HR2, HR2+HZ e HR2+LOS comparado com o grupo NR. A MVE e MVD foram maiores nos grupos HR2, HR2+HZ e HR2+LOS comparado com o grupo NR. O DTM do VE foi maior nos grupos HR1, HR2, HR2+HZ comparado com o grupo NR e HR2+LOS. DTM do VD foi maior no grupo HR2 e HR2+HZ comparado com o grupo NR, HR1 e HR2+LOS. A FI no VE e VD foi maior nos grupos HR1, HR2 e HR2+LOS comparado com o grupo NR e HR2+HZ. A expressão da proteína do receptor AT1 no VE e VD foi maior nos animais do grupo HR2 e HR2+HZ quando comparado com o grupo NR, HR1 e HR2+LOS. A expressão da proteina do receptor AT2 não foi alterada pelo alto consumo de sal, mas foi menor no grupo HR2+LOS. A ligação do anticorpo que reconhece a conformação ativada do receptor AT1 no VE e VD foi menor nos grupos HR1, HR2, HR2+HZ e HR2+LOS comparado com o grupo NR. A ligação do anticorpo que reconhece a conformação ativada do receptor AT2 não foi alterada no VE e VD dos grupos HR1, HR2 e HR2+LOS. No entanto, a ligação do anticorpo no receptor AT2 foi menor no VE e VD no grupo HR2+LOS. O conteúdo de AII foi maior em ambos os ventrículos nos grupos HR1, HR2, HR2+HZ e HR2+LOS. O elevado consumo de sal induz hipertrofia e fibrose miocárdica independente do efeito sobre a pressão arterial. A hipertrofia do cardiomiócito e a FI induzida pelo sal ocorre por mecanismos diferentes. Algumas evidências deste estudo sugerem a internalização do receptor AT1 induzido pelo sal provavelmente devido à ligação da AII. / Increased blood pressure is not the only consequence of salt overload. Independently from the hemodynamic effect, salt excess may induce structural alterations in the myocardium. The aim of the present study was to evaluate the mechanisms of the myocardium structural alteration in response to high salt intake. Male Wistar rats were fed normal (NR: 1.3% NaCl), high 1 (HR1 4%) or high 2 (HR2 8%) salt diet since weaning until 18th week of age. HR2 group was divided in HR2, HR2+hydralazine (HZ: 15mg/ kg/ dia) and HR2+losartan (LOS: 20mg/ kg/ dia). Drugs were administered since the 7th week of age. Tail-cuff blood pressure (Tc-BP), plasma renin activity (PRA), serum aldosterone (ALDO), echocardiography, left (LV) and right (RV) ventricular mass, cardiomyocyte transverse diameter (CTD), interstitial fibrosis (IF), protein expression of AT1 and AT2 receptors, angiotensin II content (AII), binding of the conformational specific anti-AT1 and anti-AT2 antibody in both ventricles were determined in the LV and RV. Tc-BP was higher in the HR1 and HR2 groups when compared to NR. Tc-BP on HR2+HZ and HR2+LOS did not differ from NR. PRA and ALDO were lower in the HR1, HR2, HR2+HZ and HR2+LOS when compared to NR. Interventricular septal and left ventricular posterior wall thicknesses were higher on HR1, HR2, HR2+HZ and HR2+LOS compared to NR. LV and RV mass was higher in the HR2, HR2+HZ and HR2+LOS when compared to NR. CTD in the LV was higher on HR1, HR2 and HR2+HZ groups than on NR and HR2+LOS groups. CTD in the RV was higher in the HR2 and HR2+HZ when compared to NR, HR1 and HR2+LOS groups. IF was higher in the LV and RV in HR1, HR2 and HR2+LOS groups than in NR and HR2+HZ groups. AT1 protein expression was higher in the HR2 and HR2+HZ compared to NR, HR1 and HR2+LOS groups. High salt intake did not increase AT2 protein expression in the HR1, HR2 and HR2+HZ groups. However, losartan induced a decrease in AT2 protein expression. In response to high salt intake, the binding of an AT1 conformational specific antibody was lower in both ventricles. Binding of the conformational specific anti-AT2 antibody in both ventricles did not change in response to HR1 and HR2. However, binding of the conformational specific anti-AT2 antibody was lower in both ventricles in the HR2+LOS group. AII was higher in both ventricles in the HR1, HR2, HR2+HZ and HR2+LOS groups. Myocardial structural alterations in response to high salt intake are independent of the effect on blood pressure. Salt induced cardiomyocyte hypertrophy and interstitial fibrosis are due to different mechanisms. Some evidences from the present study are in favor of salt induced AT1 receptor internalization probably due to AII binding.

Bnip3 is a BH3-only member of the Bcl-2 family of apoptotic proteins. Our laboratory has previously shown that Bnip3 induces a unique pathway of cardiac myocyte cell death, characterized by mitochondrial dysfunction, cytochrome c release and DNA fragmentation. Bnip3 is induced by hypoxia and the death pathway is activated by concurrent acidosis. We have shown that hypoxia-acidosis creates an environment that is permissive to calpain but not caspase activation and is characterized by enhanced DNase(s) activity as evidenced by genomic DNA fragmentation. This dissertation describes the nuclear consequences of Bnip3 activation by hypoxia-acidosis. Chapter 3 presents my evidence that hypoxia with progressive acidosis in cardiac myocytes results in a biphasic activation of DNases. In phase 1, [pH]o 6.9-6.7, apoptosis-inducing factor (AIF) is released from the mitochondria and translocates to the nucleus. AIF release coincided with the loss of mitochondrial membrane potential and with the release of cytochrome c from the mitochondria. In Phase II, [pH]o 6.3-6.0, DNase II translocates from the cytoplasm to the nuclear compartment. Nuclear localization of DNase II was associated with the collapse of endosomal pH gradients, indicated by diffuse Lysotracker Red staining and with single strand DNA nicks. Both phases of DNase release were independent of Bnip3, the mPTP and calpains. Neither phase involved activation of caspase-dependent DNases. Chapter 4 describes a unique role for Bnip3 in the modulation of histone acetylation. I found that hypoxia with acidosis in cardiac myocytes but not hypoxia alone stimulated a global increase in the acetylation of histones H3 and H4. Acetylation was initiated at [pH]o ~ 6.8 and increased as the pH declined. Histone hyperacetylation was associated with an increase in histone acetyltransferase (HAT) activity but no change in deacetylase (HDAC) activity. Knockdown of Bnip3 protein expression with siRNA dramatically reduced both histone H3 and H4 acetylation levels and HAT activity indicating an essential role for Bnip3 in this process. Components of the hypoxia-acidosis death pathway including the mPTP and calpains are not required for Bnip3-mediated histone hyperacetylation. These results reveal a novel role for Bnip3 in regulating HAT activity and histone acetylation which may lead to altered cardiac gene expression.

O aumento da pressão arterial não é a única consequência da sobrecarga de sal na dieta. Independente dos efeitos hemodinâmicos, o excesso de sal pode induzir alterações estruturais no miocárdio. A avaliação dos mecanismos destas alterações foi o objetivo do presente estudo. Para tanto, ratos Wistar machos foram alimentados com dieta: normossódica (NR: 1,3% de NaCl), hipersódica 1 (HR1: 4%) e hipersódica 2 (HR2: 8%) desde o desmame até a 18a semana de idade. O grupo HR2 foi dividido em HR2, HR2+Hidralazina (HZ: 15mg/ kg/ dia) e HR2+Losartan (LOS: 20mg/ kg/ dia). As drogas foram administradas a partir da 7a semana de idade. Foram avaliados pressão arterial caudal (PAc), atividade de renina plasmática (ARP), aldosterona sérica, ecocardiograma, massa ventricular esquerda (MVE) e direita (MVD), medida do diâmetro transverso do miócito (DTM), fibrose intersticial (FI), expressão protéica do receptor de angiotensina II do tipo I (AT1) e tipo 2 (AT2), dosagem de angiotensina II (AII) e ligação do anticorpo que reconhece a conformação ativada dos receptores AT1 e AT2 no ventrículo esquerdo (VE) e direito (VD). A PAc foi maior no grupo HR1 e HR2 comparado com o grupo NR. A PAc do grupo HR2+HZ e HR2+LOS não diferiu do grupo NR. ARP e ALDO foram menores nos grupos HR1, HR2, HR2+HZ e HR2+LOS. A espessura do septo interventricular na diástole e da parede posterior do ventrículo esquerdo na diástole foram maiores nos grupos HR1, HR2, HR2+HZ e HR2+LOS comparado com o grupo NR. A MVE e MVD foram maiores nos grupos HR2, HR2+HZ e HR2+LOS comparado com o grupo NR. O DTM do VE foi maior nos grupos HR1, HR2, HR2+HZ comparado com o grupo NR e HR2+LOS. DTM do VD foi maior no grupo HR2 e HR2+HZ comparado com o grupo NR, HR1 e HR2+LOS. A FI no VE e VD foi maior nos grupos HR1, HR2 e HR2+LOS comparado com o grupo NR e HR2+HZ. A expressão da proteína do receptor AT1 no VE e VD foi maior nos animais do grupo HR2 e HR2+HZ quando comparado com o grupo NR, HR1 e HR2+LOS. A expressão da proteina do receptor AT2 não foi alterada pelo alto consumo de sal, mas foi menor no grupo HR2+LOS. A ligação do anticorpo que reconhece a conformação ativada do receptor AT1 no VE e VD foi menor nos grupos HR1, HR2, HR2+HZ e HR2+LOS comparado com o grupo NR. A ligação do anticorpo que reconhece a conformação ativada do receptor AT2 não foi alterada no VE e VD dos grupos HR1, HR2 e HR2+LOS. No entanto, a ligação do anticorpo no receptor AT2 foi menor no VE e VD no grupo HR2+LOS. O conteúdo de AII foi maior em ambos os ventrículos nos grupos HR1, HR2, HR2+HZ e HR2+LOS. O elevado consumo de sal induz hipertrofia e fibrose miocárdica independente do efeito sobre a pressão arterial. A hipertrofia do cardiomiócito e a FI induzida pelo sal ocorre por mecanismos diferentes. Algumas evidências deste estudo sugerem a internalização do receptor AT1 induzido pelo sal provavelmente devido à ligação da AII. / Increased blood pressure is not the only consequence of salt overload. Independently from the hemodynamic effect, salt excess may induce structural alterations in the myocardium. The aim of the present study was to evaluate the mechanisms of the myocardium structural alteration in response to high salt intake. Male Wistar rats were fed normal (NR: 1.3% NaCl), high 1 (HR1 4%) or high 2 (HR2 8%) salt diet since weaning until 18th week of age. HR2 group was divided in HR2, HR2+hydralazine (HZ: 15mg/ kg/ dia) and HR2+losartan (LOS: 20mg/ kg/ dia). Drugs were administered since the 7th week of age. Tail-cuff blood pressure (Tc-BP), plasma renin activity (PRA), serum aldosterone (ALDO), echocardiography, left (LV) and right (RV) ventricular mass, cardiomyocyte transverse diameter (CTD), interstitial fibrosis (IF), protein expression of AT1 and AT2 receptors, angiotensin II content (AII), binding of the conformational specific anti-AT1 and anti-AT2 antibody in both ventricles were determined in the LV and RV. Tc-BP was higher in the HR1 and HR2 groups when compared to NR. Tc-BP on HR2+HZ and HR2+LOS did not differ from NR. PRA and ALDO were lower in the HR1, HR2, HR2+HZ and HR2+LOS when compared to NR. Interventricular septal and left ventricular posterior wall thicknesses were higher on HR1, HR2, HR2+HZ and HR2+LOS compared to NR. LV and RV mass was higher in the HR2, HR2+HZ and HR2+LOS when compared to NR. CTD in the LV was higher on HR1, HR2 and HR2+HZ groups than on NR and HR2+LOS groups. CTD in the RV was higher in the HR2 and HR2+HZ when compared to NR, HR1 and HR2+LOS groups. IF was higher in the LV and RV in HR1, HR2 and HR2+LOS groups than in NR and HR2+HZ groups. AT1 protein expression was higher in the HR2 and HR2+HZ compared to NR, HR1 and HR2+LOS groups. High salt intake did not increase AT2 protein expression in the HR1, HR2 and HR2+HZ groups. However, losartan induced a decrease in AT2 protein expression. In response to high salt intake, the binding of an AT1 conformational specific antibody was lower in both ventricles. Binding of the conformational specific anti-AT2 antibody in both ventricles did not change in response to HR1 and HR2. However, binding of the conformational specific anti-AT2 antibody was lower in both ventricles in the HR2+LOS group. AII was higher in both ventricles in the HR1, HR2, HR2+HZ and HR2+LOS groups. Myocardial structural alterations in response to high salt intake are independent of the effect on blood pressure. Salt induced cardiomyocyte hypertrophy and interstitial fibrosis are due to different mechanisms. Some evidences from the present study are in favor of salt induced AT1 receptor internalization probably due to AII binding.

Swelling-activated Cl- current (ICl,swell) is an outwardly rectifying Cl- current that influences cardiac electric activities and acts as a potential effector of mechanoelectrical feedback that antagonizes the effects of stretch-activated cation channels. Persistent activation of ICl,swell has been observed in multiple models of cardiovascular diseases. Previously we showed that angiotensin II (AngII) signaling and reactive oxygen species (ROS) produced by NADPH oxidase (NOX) are involved in the activation of ICl, swell by both beta1-integrin stretch and osmotic swelling. Because endothelin-1 (ET-1) is a potential downstream mediator of AngII and ETA receptor blockade abrogates AngII-induced ROS generation, we studied how ET-1 signaling regulates ICl,swell and the relationship between AngII and ET-1 signaling. Under isosmotic conditions, ET-1 elicited an outwardly rectifying Cl- current that was fully blocked by the highly selective ICl,swell inhibitor DCPIB and by osmotic shrinkage. Selective ETA blockade (BQ123), but not ETB blockade (BQ788), fully suppressed the ET-1-induced current. ET-1-induced ICl,swell was abolished by blockade of EGFR kinase (AG1478) and PI-3K inhibitors (LY294002 and wortmannin), which also suppress beta1-integrin stretch- and swelling-induced ICl,swell. ET-1-induced ICl,swell was abrogated by ebselen, a membrane-permeant glutathione peroxidase mimetic that dismutates H2O2 to H2O, suggesting that ROS were required intermediates in ET-1-induced activation of ICl,swell. Both NOX and mitochondria are important sources of ROS in cardiomyocytes. Blocking NOX with apocynin or mitochondrial complex I with rotenone both completely suppressed ET-1-induced ROS generation and activation of ICl,swell, indicating that ROS from both NOX and mitochondria were required to activate ICl,swell, and complete block by inhibitors of either ROS source suggests mitochondrial and NOX must act in series rather than in parallel. ICl,swell elicited by antimycin A, which stimulates superoxide production by mitochondrial complex III, was insensitive to NOX inhibitor apocynin and the NOX fusion peptide inhibitor gp91ds-tat. Activation of ICl,swell induced by diazoxide, which stimulates mitochondrial ROS production by opening mitochondrial KATP channels, was not affected by gp91ds-tat. These data suggests that mitochondrial ROS is downstream from NOX in the regulation of ICl,swell. Mitochondrial ROS production that is enhanced by NOX ROS is likely to be responsible for the activation of ICl,swell by ET-1. In order to determine the role of ERK in the proposed signaling pathway that regulates ICl,swell, we examined the effect of ERK inhibitors (PD 98059 and U0216) on the activation of ICl,swell elicited by ET-1, EGF, and H2O2. ERK inhibitors partially blocked ET-1-induced ICl,swell but fully inhibited activation of ICl,swell in response to EGF. However, ERK inhibitors did not affect ICl,swell elicited by exogenous H2O2. We also established the the relationship of ET-1 to AngII and osmotic swelling in the regulation of ET-1 ICl,swell. ETA blockade abolished ICl,swell elicited by both AngII and osmotic swelling, whereas AT1 blockade did not effect ET-1-induced ICl,swell, suggesting that ET-1 signaling is downstream from AngII and osmotic swelling. HL-1 cell is a murine atrial cell line that retain phenotypic characteristics of adult cardiomyocytes. We showed that osmotic swelling and ET-1 turned on DCPIB-sensitive outwardly rectifying Cl- current in HL-1 cells with both physiological and symmetrical Cl- gradients. The swelling-induced current was suppressed by gp91ds-tat and rotenone but insensitive to apocynin. Blockade of ETA receptor (BQ123) and NOX (gp91ds-tat) completely inhibited ET-1-induced ICl,swell in HL-1 cells. These data indicate that ICl,swell is present in HL-1 cell and regulated by similar mechanisms as in native cells. Finally, we confirmed the production of ROS by ET-1 signaling by flow cytometry of HL-1 cells using the nominally H2O2-selective fluorescent probe C H2DCFDA-AM. Exposure to ET-1 increased ROS production, as did H2O2, a positive control. ET-1-induced ROS production was fully suppressed by both gp91ds-tat and rotenone. HL-1 cell ROS production also was stimulated by the mitochondrial complex III inhibitor antimycin A, and antimycin A-induced ROS production was blocked by rotenone but not by gp91ds-tat. These data suggest that ET-1 ETA receptor signaling elicits ICl,swell by sequentially stimulating ROS production by NOX and mitochondria. ETA receptor signaling is down stream from AngII in the osmotic swelling-induced activation of ICl,swell and is upstream from EGFR kinase and PI-3K. Endothelin signaling is likely to be an important means of activating ROS production and ICl,swell in a variety of cardiovascular diseases.

[Truncated abstract] The innate ability of the heart to compensate for an increase in workload as a result of disease or injury, through an increase in size and mass is known as cardiac hypertrophy. The hypertrophy of the heart compensates for an increase in workload with an increase in cardiac output. However, excessive hypertrophy can result in cardiac dysfunction and substantially increases the risk of cardiac failure and mortality. The molecular mechanisms that regulate the development of cardiac hypertrophy and cardiac failure are not entirely understood. Traditionally, the G-protein Coupled Receptor (GPCR) and the downstream Mitogen-Activated Protein Kinase (MAPK) family of proteins have been implicated. However, elevated circulating and ventricular levels of several classes of cytokines also suggested that signaling by the downstream effectors of cytokine receptors, such as the Signal Transducers and Activators of Transcription (STATs), may be important. The aim of this thesis was, therefore, to characterize the involvement of MAPK and STAT pathways in regulating cardiac hypertrophy and cardiac failure. A function for MAPK and STAT signaling in regulating cardiac hypertrophy stimulated by the inflammatory cytokine IL-1Β was initially defined in primary cultures of neonatal rat cardiac myocytes. In this study, it was demonstrated that the chemical inhibition of ERK or p38MAPK was sufficient to inhibit IL-1Β-stimulated ANF expression. In contrast, simultaneous inhibition of both ERK and p38MAPK was required to ablate the hypertrophic morphology of cardiac myocytes treated with IL-1Β. These results demonstrated differential signaling from the MAPK isoforms in regulating the gene expression and morphological components of cardiac hypertrophy. In addition, it was revealed that IL-1Β treatment resulted in a delayed response (>60 min) in STAT3α tyrosine phosphorylation, which was subsequently shown to require the initial rapid activation of either ERK or p38MAPK. IL-1Β-stimulated STAT3 phosphorylation was also dependent on the de novo synthesis of secondary signaling molecules. The ablation of the STAT3 tyrosine phosphorylation by the inhibition of ERK or p38MAPK activity, correlated with the attenuation of IL-1Β-stimulated ANF expression, suggesting that signaling through STAT3α may be involved in regulating gene expression associated with IL-1Β cardiac hypertrophy

Abstract Excitation-contraction coupling (ECC) is a process linking the electrical excitation of the muscle cell (myocyte) membrane to the contraction of the cell. In this study the possibilities of mathematical modeling were studied in current ECC research. Mathematical modeling was employed in two distinct ECC research areas, the enzymatic regulation of ECC and ECC during cardiac myocyte development. Despite the distinction, both of these are extremely complex biological systems characterized by diverse and partly contradictory reported experimental results, with a large part based on genetically engineered animal models. Novel mathematical models were developed for both of these research areas. The model of ventricular myocyte ECC with calmodulin-dependent protein kinase II (CaMKII)-mediated regulation faithfully reproduced the heart-rate dependent regulation of ECC. This regulation is thought to be the major effect of CaMKII-mediated regulation. The model of the embryonic ventricular myocyte provided the first comprehensive system analysis of how the embryonic heartbeat is generated at the cellular level. A similar type of model was also developed to show the notable differences between neonatal and adult ventricular myocyte ECC. The mathematical models of ECC presented in this study were further used to simulate ECC in genetically engineered myocytes. The cellular mechanisms of genetically engineered animal models could be better understood by employing mathematical modeling in parallel to experimental characterization of the animal model. It was found in simulations that the indirect consequences and the compensatory mechanisms induced by genetic modification may have a more significant effect on ECC than the direct consequences of the modification. To understand the overwhelming complexity of biological systems including ECC, competent system analysis tools, such as mathematical modeling, are required. The purpose of mathematical modeling is not to replace the experimental studies, but to provide a more comprehensive system analysis based on the experimental data. This system analysis will help in planning subsequent experiments needed to gain the most relevant information about the studied biological system.

Orientadores: José Wilson Magalhães Bassani, Rosana Almada Bassani / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-26T11:22:43Z (GMT). No. of bitstreams: 1 Milan_HugoFernandoMaia_M.pdf: 2735459 bytes, checksum: 650eb9ee4f85d8ff73ae612f72ae3534 (MD5) Previous issue date: 2015 / Resumo: Tendo em vista que a estimulação com campos elétricos externos (E) é utilizada na prática clínica para tratamento de arritmias cardíacas, é necessário um melhor entendimento do fenômeno de polarização da membrana plasmática de cardiomiócitos por E. O disparo de potencial de ação, e subsequente contração celular, induzido por E em cardiomiócitos depende da indução de variação do potencial elétrico transmembrana (?Vm) que leve este potencial ao valor limiar. Devido às limitações dos métodos atualmente disponíveis para medir ?Vm e seu valor máximo, ?Vmax, os modelos eletromagnéticos representam uma importante ferramenta para sua estimativa. Porém, os valores calculados dependem de como o fenômeno de polarização da membrana é modelado. Os modelos eletromagnéticos encontrados na literatura aproximam a forma irregular do cardiomiócito a formas geométricas regulares. Entretanto, até o momento, não se sabe qual destes modelos é o mais adequado para se estimar ?Vm. As células miocárdicas apresentam irregularidades em sua forma e, tanto a forma quanto as dimensões das células alteram-se com o desenvolvimento pós-natal. Neste trabalho, foi desenvolvido um modelo numérico tridimensional (MN3D) da forma irregular da célula, e comparou-se as estimativas de ?Vm induzida por E limiar (?VL) feitas com este modelo e com modelos simplificados, entre estes o modelo numérico bidimensional (MN2D) e os modelos analíticos para cilindro (MACil), esfera (MAEsf), esferóide prolato (MAEsPr) e elipsóide (MAElip). Para estimar ?VL, E limiar e as dimensões celulares foram medidos em células cardíacas isoladas de ratos neonatos (5-7 dias), infantes (28-32 dias) e adultos (4-6 meses), em 6 faixas de ângulos entre a direção de aplicação do campo e o eixo maior da célula. Os modelos foram calibrados do ponto de vista eletromagnético, o que mostrou que, MN2D e MACil são inadequados para estimar ?Vmax. Enquanto as estimativas de ?VL com MN3D e MAEsPr não variaram com o ângulo, mas sim com a idade, o oposto ocorreu com as estimativas feitas com o MAElip. Dentro de certas condições, as estimativas de ?VL feitas com MAEsPr foram as mais próximas daquelas feitas com MN3D. Conclui-se que o MAEsPr, menos complexo tecnicamente, pode fornecer estimativas confiáveis de ?VL, desde que o ângulo de aplicação de E seja pequeno (até 30º) / Abstract: Considering that stimulation with external electrical fields (E) is clinically used for arrhythmia treatment, it is important to understand the phenomenon of membrane polarization by E. Action potential and contraction triggering by E in cardiomyocytes depends on the induction of a transmembrane potential variation (?Vm) sufficient for the attainment of the excitation threshold. Due to the limitations of the methods currently available for measurement of ?Vm and its maximum value, ?Vmax, electromagnetic models represent an important tool for this purpose. However, the calculated values depend on how the membrane polarization phenomenon is modeled. The electromagnetic models available in the literature approximate the cardiomyocyte irregular shape to regular geometries. Nevertheless, it has not been ascertained yet which model is the most appropriated to estimate ?Vmax in these cells, of which both dimensions and shape vary markedly during postnatal development, and often present geometric irregularities. Thus, approximation of the cell shape to regular geometries may result in a considerable error in the ?Vm estimation. The aim of this study was to develop a three-dimensional numerical model (MN3D) based on the irregular cell shape and to compare the values of ?Vmax induced by the threshold E (?VL) estimated with this model with those calculated with simplified models, such as the twodimensional numerical model (MN2D) and the analytical models for cylinder (MACil), sphere (MAEsf), prolate spheroid (MAEsPr), and ellipsoid (MAElip). To estimate ?VL, the threshold E and cell dimensions were measured in cardiomyocytes isolated from neonatal (5-7 days), weaning (28-32 days) and adult (4-6 months) rats, for 6 ranges of the angle between the directions of E and the cell major axis. Electromagnetic calibration of the models showed that MN2D and MACil were not suitable for ?Vmax estimation in these cells. While ?VL estimated with MN3D and MAEsPr were angle-independent, but dependent on the animal's age, the opposite was observed regarding the estimates made with MAElip. Under certain conditions, ?VL values estimated with MAEsPr were the closest to those obtained with MN3D. It is concluded that MAEsPr, a less technically complex model, can provide reliable ?VL estimates provided that the angle between the directions of E and the cell major axis is small (up to 30º) / Mestrado / Engenharia Biomedica / Mestre em Engenharia Elétrica

No description available.