Dois tipos de memórias contráteis em miocárdio de mamífero

• Ano de defesa: 2011
• Autor(a) principal: Souza, Rejane Cardoso
• Orientador(a): Garcia, Eduardo Antônio Conde
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Sergipe
• Programa de Pós-Graduação: Pós-Graduação em Ciências da Saúde
• País: BR
• Palavras-chave em Português: Miocárdio; Contratilidade; Memória depressora; Memória excitadora; Cobaia
• Palavras-chave em Inglês: Myocardium; Contractility; Depressant memory; Excitatory memory; Guinea pig
• Área do conhecimento CNPq: CNPQ::CIENCIAS DA SAUDE
• Link de acesso: https://ri.ufs.br/handle/riufs/3695

In the heart, the existence of an electrical memory was firstly reported by Rosenbaum et al. (1982), but Rios et al. (1975) and Garcia Moreira (1977) were those that firstly described the existence of contractile memories in the amphibian myocardium. These authors developed a mathematical model for representing such phenomenon. In the present study, we aimed to characterize two kinds of contractile memories occurring in the mammalian myocardium. One of them, depresses the tissue (the depressant memory, DM) and the other one acts by stimulating it (the excitatory memory, EM). The pivotal rationale guiding this work was: when the heart is challenged by changing the environment sources like nutrients, chemicals, temperature, etc., its behavior changes in order to optimize the energy expenditure associated with its contractility. This adaptation process allows to be reached a new state of dynamic equilibrium. In order to express such behavior, the tissue creates contractile memories for adjusting the amplitude of myocardial forces. This is provided by balancing the load of DM and EM available at each myocardial beat. The expression and accumulation of these memories were studied in the guinea pig atria submitted to the experimental protocols described previously by Seed & Walker (1988), Shimizu (2000), and Conde-Garcia (not published). The expression and accumulation of myocardial memories were described by employing two static descriptors, LODMmax and LOEMmax. They stand for the maximum load of depressant memory and the maximum load of excitatory memory, respectively. Furthermore, another pair of dynamic descriptors was also used to measure the maximum rate of erasing of the depressant memory (MREDM) and the other one to measure the maximum rate of erasing of the excitatory memory (MREEM). The static descriptors represent the transference of load of both memories but the dynamic descriptors were related to the rate of erasing of such memories. Our results brought us onto the following conclusions: 1. contractile memories are a phenomenon apart from the electrical memory because rising the external potassium from 2.7 to 7.0 mM did not modify (n n = 4) LODMmax that changed from 82,09 ± 1,58 to 81,56 ± 2,01% (p > 0,05), LOEMmax from 83,36 ± 0,56 to 90,12 ± 17,92% (p > 0,05), MREDM changed from -1,36 ± 0,67 to -1,13 ± 0,42gf/s (p > 0,05), and MREED from -2,09 ± 1,65 to -1,56 ± 1,41gf/s (p > 0,05). 2. However, the expression and accumulation of DM and EM are affected by the intracellular calcium transient. The increase of extracellular calcium from 1,37 to 5,47mM (n = 3) reduced LODMmax: from 87,56 ± 2,33 to 63,83 ± 3,78% (p < 0,05); LOEMmax from 84,36 ± 0,54 to 13,91 ± 0,11% (p < 0,05); MREDM from -2,58 ± 0,71 to -1,20 ± 0,37gf/s (p < 0,05) and MREEM from -0,90 ± 0,13 to -0,34 ± 0,05 gf/s (p < 0,05). Adding 5mM cafeine to the bath solution also reduced LODMmax from 79,88 ± 3,48 to 56,68 ± 6,62% (p < 0,05); LOEMmax from 77,14 ± 1,02 to 28,54 ± 2,11% (p < 0,05); MREDM from -1,78 ± 0,50 to -0,60 ± 0,10 gf/s (p < 0,05), and MREED from -1,74 ± 0,64 to -0,33 ± 0,14 gf/s (p < 0,05); 3. In the experimental condition employed in this work, a given beat receives both depressant and excitatory information built by the last ten beats.