A low-cost 2-D sarcomere model to demonstrate titin-related mechanisms for force production.

Given the recently proposed three-filament theory of muscle contraction, we present a low-cost physical sarcomere model aimed at illustrating the role of titin in the production of active force in skeletal muscle. With inexpensive materials, it is possible to illustrate actin-myosin cross-bridge interactions between the thick and thin filaments and demonstrate the two different mechanisms by which titin is thought to contribute to active and passive muscle force. Specifically, the model illustrates how titin, a molecule with springlike properties, may increase its stiffness by binding free calcium upon muscle activation and reducing its extensible length by attaching itself to actin, resulting in the greater force-generating capacity after an active than a passive elongation that has been observed experimentally. The model is simple to build and manipulate, and demonstration to high school students was shown to result in positive perception and improved understanding of the otherwise complex titin-related mechanisms of force production in skeletal and cardiac muscles.NEW & NOTEWORTHY Our physical sarcomere model illustrates not only the classic view of muscle contraction, the sliding filament and cross-bridge theories, but also the newly discovered role of titin in force regulation, called the three-filament theory. The model allows for easy visualization of the role of titin in muscle contraction and aids in explaining complex muscle properties that are not captured by the traditional cross-bridge theory.

emperature, pH and sarcomere length of Caiman yacare in different body weight categories at slaughter / Temperatura, pH e comprimento de sarcômero de Caiman yacare em diferentes categorias de peso corporal ao abate

The objective of this work was to characterize the internal temperature of the carcass, pH and sarcomere length in four categories of body weight at a slaughter. The categories were: category 1, animals up to 1.5 kg, category 2, animals from 1.501 to 2.5 kg, category 3, animals from 2.501 to 3.5 kg and category 4, animals over 3.501 kg. The time intervals evaluated were 0.5, 2, 4, 6, 8, 10, 12, 14, 16, 18, 24 and 36 hours after bleeding, therefore, a factorial scheme (4 x 12) was used, in which where four categories of pre-slaughter weight and the behavior of the carcasses during the post-slaughter time were evaluated. There was no interaction effect between the weight categories and the time for the variation of the carcass internal temperature, pH and sarcomere length, but when only the time of rigor was evaluated, there were significant differences for the analyzed parameters. The internal temperature of the initial average carcass (0.5 hours) was 16.02°C, reaching 3.80°C at 36 hours post-slaughter. In addition, the lowest average pH found was at 24 hours, with a value of 5.39. Regarding the sarcomere length, the smallest mean length observed was 1.41 µm at 16 hours post-slaughter and the final mean length (36 hours) was 1.89 µm. It was concluded that the analyzed margin of the categories of body weight at slaughter did not interfere in the variation of temperature, pH and sarcomere length during the post-mortem of the Pantanal caiman.(AU)

O objetivo do trabalho foi caracterizar a temperatura interna da carcaça, o pH e o comprimento de sarcômero em quatro categorias de peso corporal ao abate. As categorias foram: categoria 1, animais com até 1,5 kg, categoria 2, animais de 1,501 a 2,5 kg, categoria 3, animais de 2,501 a 3,5 kg e categoria 4, animais acima de 3,501 kg. Os intervalos de tempo avaliados foram 0,5, 2, 4, 6, 8, 10, 12, 14, 16, 18, 24 e 36 horas, após a sangria, portanto, foi utilizado um esquema fatorial (4 x 12) que avaliou quatro categorias de peso e o comportamento das carcaças ao decorrer do tempo. Não houve efeito de interação entre as categorias de peso e o tempo para a variação da temperatura interna da carcaça, pH e comprimento de sarcômero, mas quando avaliado apenas o tempo de rigor, houve diferenças significativas para os parâmetros analisados. A temperatura interna da carcaça média inicial (0,5 horas) foi de 16,02°C, chegando a 3,80°C nas 36 horas pós-abate. Além disso, o menor pH médio encontrado foi as 24 horas, com valor de 5,39. Em relação ao comprimento de sarcômero o menor comprimento médio observado foi de 1,41 µm nas 16 horas pós-abate e o comprimento médio final (36 horas) foi de 1,89 µm. Conclui-se que a margem analisada das categorias de peso corporal ao abate, não interferiram na variação de temperatura, pH e comprimento de sarcômero durante o post mortem do jacaré-do-Pantanal.(AU)

Chronic uphill and downhill exercise protocols do not lead to sarcomerogenesis in mouse skeletal muscle.

It has been suggested that eccentric contraction (EC) is associated with increases in serially arranged sarcomeres (sarcomerogenesis), while concentric contraction (CC) has been associated with serial sarcomeres decrease. Sarcomerogenesis following EC is thought to be a protective muscle adaptation, preventing muscle injury in future eccentric exercise bouts (repeated bout effect). However, the mechanisms underlying sarcomerogenesis in EC remain unknown, and the sarcomerogenic responses observed in response to EC and CC are contradictory. We measured sarcomere length, sarcomere length uniformity, serial sarcomere number, and fascicle length in gastrocnemius medialis, tibialis anterior, vastus medialis and vastus lateralis in sedentary (SED) mice, and in mice following protocols of moderate uphill (TRU) and downhill (TRD) training and uphill (OTU) and downhill (OTD) overtraining. We found pain sensitivity after the first bout of EC exercise on TRD and OTD followed by a normalized sensory response after four weeks of training, indicating a repeated bout effect. However, these findings were not associated with sarcomerogenesis, as serial sarcomere numbers did not increase in TRD and OTD skeletal muscle samples compared to controls (SED). However, we found a decrease in serial sarcomere number in VL and TA in OTU group mice, which was associated with a decrease in fascicle length and no change of sarcomere length at the tested joint configuration. We conclude that excessive concentric muscle contraction (OTU group mice), leads to a decrease in serial sarcomere number, while moderate or excessive eccentric training, did not result in sarcomerogenesis, as reported in the literature.

Muscle residual force enhancement: a brief review.

Muscle residual force enhancement has been observed in different muscle preparations for more than half a century. Nonetheless, its mechanism remains unclear; to date, there are three generally accepted hypotheses: 1) sarcomere length non-uniformity, 2) engagement of passive elements, and 3) an increased number of cross-bridges. The first hypothesis uses sarcomere non-homogeneity and instability to explain how "weak" sarcomeres would convey the higher tension generated by an enhanced overlap from "stronger" sarcomeres, allowing the whole system to produce higher forces than predicted by the force-length relationship; non-uniformity provides theoretical support for a large amount of the experimental data. The second hypothesis suggests that passive elements within the sarcomeres (i.e., titin) could gain strain upon calcium activation followed by stretch. Finally, the third hypothesis suggests that muscle stretch after activation would alter cross-bridge kinetics to increase the number of attached cross-bridges. Presently, we cannot completely rule out any of the three hypotheses. Different experimental results suggest that the mechanisms on which these three hypotheses are based could all coexist.

Expressão imunoistoquímica de diferenciação e crescimento celular em cardiomiócitos de neonatos / Immunohistochemical expression of cell differentiation and growth in neonate cardiomyocytes

FUNDAMENTO: As alterações cardíacas na fase de transição do coração fetal para a vida extrauterina vêm sendo exploradas por inúmeras pesquisas em animais, e os mecanismos celulares responsáveis por essas modificações ainda não estão bem documentado em seres humanos. OBJETIVO: Avaliar o mecanismo de diferenciação celular em cardiomiócitos ocorridas nos primeiros dias de vida, por meio da análise imunoistoquímica de proteínas envolvidas com processos de proliferação e contração muscular, em amostras de miocárdio de recém-natos humanos. MÉTODO: Estudo transversal de amostras parafinadas de miocárdio provenientes de banco de necropsias de recémnascidos humanos, divididos em dois grupos amostrais: recém-nascidos a termo que foram a óbito com no máximo dois dias de vida (NEO1) com 10 casos, e recém- nascidos a termo que foram a óbito entre três e 10 dias de vida (NEO2) com 14 casos, a fim de seguir uma linha de tempo que contemplasse a fase de transição da circulação fetal a vida extrauterina. As amostras foram estudadas em tissue microarray e os anticorpos utilizados foram o Ki67, PCNA, PTEN, Bcl2 (proliferação) e HHF35 e actina sarcomérica (proteínas contráteis). RESULTADOS: Foi encontrada diferença com o Ki67 p = 0,02, HHF35 p < 0,01 e actina sarcomérica p = 0,02, e a expressão do Ki67 foi mais alta no grupo NEO1 e a expressão do HHF35 e da actina sarcomérica foi mais alta no grupo NEO2. CONCLUSÃO: Os resultados sugerem que os cardiomiócitos apresentam uma característica proliferativa (Ki67) nos NEO1 e que essa vai, seguindo uma linha temporal, sendo substituída por um caráter de diferenciação (HHF35 e actina sarcomérica) nos NEO2.

BACKGROUND: The cardiac alterations during the fetal heart transition to extrauterine life have been explored by several animal studies and the cell mechanisms responsible for these modifications are not well documented in humans. OBJECTIVE: To evaluate the mechanism of cell differentiation into cardiomyocytes that occur in the first days of life, through immunohistochemical analysis of proteins involved in proliferation and muscle contraction processes, in samples of human neonate myocardium. METHODS: Cross-sectional study of paraffin-sample sections of myocardium from an autopsy database of human neonates, divided into two sample groups: full-term neonates who died after a maximum of two days of life (NEO1) with 10 cases, and full-term infants who died between 3 and 10 days of life (NEO2) with 14 cases, in order to follow a temporal line that would contemplate the transition from fetal circulation to extrauterine life. The samples were studied in tissue microarray and the antibodies used were Ki67, PCNA, PTEN, Bcl2 (proliferation), HHF35 and sarcomeric actin (contractile proteins). RESULTS: Difference was observed regarding Ki67, p = 0.02; HHF35, p <0.01 and sarcomeric actin, p = 0.02, with Ki67 expression being higher in NEO1 group, whereas HHF35 and sarcomeric actin expression was higher in the NEO2 group. CONCLUSION: The results suggest that cardiomyocytes have a proliferation characteristic (Ki67) in NEO1 which, following a temporal line, will be replaced by a differentiation characteristic (HHF35 and sarcomeric actin) in NEO2.

Immunohistochemical expression of cell differentiation and growth in neonate cardiomyocytes.

BACKGROUND: The cardiac alterations during the fetal heart transition to extrauterine life have been explored by several animal studies and the cell mechanisms responsible for these modifications are not well documented in humans. OBJECTIVE: To evaluate the mechanism of cell differentiation into cardiomyocytes that occur in the first days of life, through immunohistochemical analysis of proteins involved in proliferation and muscle contraction processes, in samples of human neonate myocardium. METHODS: Cross-sectional study of paraffin-sample sections of myocardium from an autopsy database of human neonates, divided into two sample groups: full-term neonates who died after a maximum of two days of life (NEO1) with 10 cases, and full-term infants who died between 3 and 10 days of life (NEO2) with 14 cases, in order to follow a temporal line that would contemplate the transition from fetal circulation to extrauterine life. The samples were studied in tissue microarray and the antibodies used were Ki67, PCNA, PTEN, Bcl2 (proliferation), HHF35 and sarcomeric actin (contractile proteins). RESULTS: Difference was observed regarding Ki67, p = 0.02; HHF35, p <0.01 and sarcomeric actin, p = 0.02, with Ki67 expression being higher in NEO1 group, whereas HHF35 and sarcomeric actin expression was higher in the NEO2 group. CONCLUSION: The results suggest that cardiomyocytes have a proliferation characteristic (Ki67) in NEO1 which, following a temporal line, will be replaced by a differentiation characteristic (HHF35 and sarcomeric actin) in NEO2.

The intimate nature of oculomotor muscles contracture.

The author makes comments about the shortening and loss of elasticity of the oculomotor muscle that remains slack for some time (contracture), by means of a reasoning based on the Hooke s law and on the papers carried out to demonstrate that a muscle that remains relaxed for some time suffers a shortening due to loss of sarcomeres on the longitudinal direction and the increase of the cross-sectional area due to the increase of collagen tissue in the perimysium and the endomysium.

Princípios fisiológicos do aquecimento e alongamento muscular na atividade esportiva[revisão] / Physiological principles of warm-up and muscle stretching on sports activities

O objetivo deste estudo foi revisar a importância do aquecimento e alongamento muscular na prática esportiva, destacando seus principais efeitos fisiológicos e benefícios, haja vista que o presente assunto tem causado muita dúvida aos atletas profissionais ou amadores bem como em profissionais da área da saúde na realização e prescrição, respectivamente, da prática do aquecimento e alongamento muscular. Foram utilizados 52 textos, entre artigos da base de dados PubMed e livros publicados de 1978 a 2008. Do total, 18 (34,62 por cento) estavam em português e 34 (65,38 por cento) em inglês. Resultados mostraram que o aquecimento tem por principal objetivo prevenir lesões devido à sua gama de efeitos fisiológicos. A realização do alongamento no término do gesto esportivo tem por finalidade evitar o encurtamento muscular, ou se realizado diariamente e por um longo período, favorecer o aumento do número de sarcômeros e, consequentemente, proporcionar um ganho de flexibilidade.

The purpose of this study was to analyze the importance of warming-up and muscle stretching on sports practice, highlighting its main physiological effects and benefits, since the present issue has caused much doubt to professional or amateur athletes as well as to professionals of the health field on designing and prescribing warming-up and muscle stretching, respectively. For this purpose, 52 texts, including articles from PubMed database and books published from 1978 to 2008, were used. From de total, 18 (34.62 percent) were written in Portuguese and 34 (65.38 percent) in English. Results showed that warming-up has the main objective to prevent injuries due to its multitude of physiological effects. The performance of stretching in the end of the sportive gesture has the purpose to prevent muscular shortening, or if carried out daily and for a long period, to provide increase in the number of sarcomeres and consequently to provide flexibility gain.

The intimate nature of oculomotor muscles contracture / A natureza íntima da contratura do músculo oculomotor

The author makes comments about the shortening and loss of elasticity of the oculomotor muscle that remains slack for some time (contracture), by means of a reasoning based on the Hooke´s law and on the papers carried out to demonstrate that a muscle that remains relaxed for some time suffers a shortening due to loss of sarcomeres on the longitudinal direction and the increase of the cross-sectional area due to the increase of collagen tissue in the perimysium and the endomysium.

O autor procura demonstrar a razão da perda de elasticidade e do encurtamento do músculo oculomotor que permanece relaxado durante certo tempo (contratura), mediante raciocínio baseado na lei de Hooke e nos trabalhos que demonstram que o músculo oculomotor que permanece frouxo por algum tempo sofre encurtamento devido à perda de sarcômeros no sentido longitudinal e ao aumento da área da secção transversa, devida ao aumento do tecido colágeno do perimísio e do endomísio.

Cruzamento industrial sobre as características de carcaça e da carne de novilhas precoces / Industrial crossbreeds on carcass and meat characteristics of veal heifers

O experimento foi realizado com o objetivo de comparar as características de carcaça e da carne de 18 novilhas dos cruzamentos comerciais: ½ Nelore ½ Limousin (L), ½ Limousin » Red Angus » Nelore (LR), e ⅝ Red Angus ⅜ Nelore (RNR). As novilhas foram confinadas aos 18 meses de idade, com média de peso de 280 ± 8,4 kg, durante 112 dias. Após o abate e resfriamento das carcaças foram avaliados: rendimento (RC), área de olho de lombo (AOL), espessura de coxão (EC), cobertura de gordura (CG), comprimento de carcaça e perna, percentagem de músculo, ossos e gordura. Das amostras do Longissimus dorsi foram analisados a composição centesimal, o pH, a perda de água, a força de cisalhamento (FC), o comprimento de sarcômero (CS) e o índice de fragmentação miofibrilar (IFM). Os dados obtidos foram submetidos à análise de variância, e as médias comparadas pelo teste de Tukey a 5% de significância. O cruzamento LR apresentou as melhores características de carcaça e de carne com 54,72% de RC; 27,87 cm de EC; 4,53 cm de CG; 63,65 cm2 de AOL; 64,58% de carne magra; 26,63% de perda de água; pH de 5,72; 2,49 kg de FC; 1,91 microm de CS; e 83,59 de IFM.(AU)

The experiment was carried out with the objective of comparing carcass and meat characteristics of 18 heifers from the following industrial crossbreeds: ½ Nelore ½ Limousin (L), ½ Limousin » Red Angus » Nelore (LR), and ⅝ Red Angus ⅜ Nelore (RNR). The heifers were confined at 18 months of age, weighing 280 ± 8.4 kg, during 112 days. After slaughter and carcass cooling, the following traits were evaluated: carcass yield (CY); rib eye area (REA); cushion thickness (CT); fat thickness (FT); carcass length (CL) and leg length (LL); muscle, bone and fat percentages. From Longissimus dorsi muscle samples, the following traits were evaluated: aproximate composition; pH; water loss; shear force (SF); sarcomere length (SL); myofibril fragmentation index (MFI). The data were submitted to analysis of variance and the means were compared by Tukeys test at 5% significance. The LR crossbreed showed the best carcass and meat characteristics, with CY=54.72%, CT=27.87 cm, FT=4.53 cm, REA=63.65 cm2, lean meat=64.58%, water loss=26.63%, pH=5.72; SF=2.49 kg, SL=1.91 microm and MFI=83.59.(AU)

Cruzamento industrial sobre as características de carcaça e da carne de novilhas precoces / Industrial crossbreeds on carcass and meat characteristics of veal heifers

O experimento foi realizado com o objetivo de comparar as características de carcaça e da carne de 18 novilhas dos cruzamentos comerciais: ½ Nelore ½ Limousin (L), ½ Limousin » Red Angus » Nelore (LR), e ⅝ Red Angus ⅜ Nelore (RNR). As novilhas foram confinadas aos 18 meses de idade, com média de peso de 280 ± 8,4 kg, durante 112 dias. Após o abate e resfriamento das carcaças foram avaliados: rendimento (RC), área de olho de lombo (AOL), espessura de coxão (EC), cobertura de gordura (CG), comprimento de carcaça e perna, percentagem de músculo, ossos e gordura. Das amostras do Longissimus dorsi foram analisados a composição centesimal, o pH, a perda de água, a força de cisalhamento (FC), o comprimento de sarcômero (CS) e o índice de fragmentação miofibrilar (IFM). Os dados obtidos foram submetidos à análise de variância, e as médias comparadas pelo teste de Tukey a 5% de significância. O cruzamento LR apresentou as melhores características de carcaça e de carne com 54,72% de RC; 27,87 cm de EC; 4,53 cm de CG; 63,65 cm2 de AOL; 64,58% de carne magra; 26,63% de perda de água; pH de 5,72; 2,49 kg de FC; 1,91 microm de CS; e 83,59 de IFM.

The experiment was carried out with the objective of comparing carcass and meat characteristics of 18 heifers from the following industrial crossbreeds: ½ Nelore ½ Limousin (L), ½ Limousin » Red Angus » Nelore (LR), and ⅝ Red Angus ⅜ Nelore (RNR). The heifers were confined at 18 months of age, weighing 280 ± 8.4 kg, during 112 days. After slaughter and carcass cooling, the following traits were evaluated: carcass yield (CY); rib eye area (REA); cushion thickness (CT); fat thickness (FT); carcass length (CL) and leg length (LL); muscle, bone and fat percentages. From Longissimus dorsi muscle samples, the following traits were evaluated: aproximate composition; pH; water loss; shear force (SF); sarcomere length (SL); myofibril fragmentation index (MFI). The data were submitted to analysis of variance and the means were compared by Tukey’s test at 5% significance. The LR crossbreed showed the best carcass and meat characteristics, with CY=54.72%, CT=27.87 cm, FT=4.53 cm, REA=63.65 cm2, lean meat=64.58%, water loss=26.63%, pH=5.72; SF=2.49 kg, SL=1.91 microm and MFI=83.59.

Different fibre populations distinguished by their calcium transient characteristics in enzymatically dissociated murine flexor digitorum brevis and soleus muscles.

Enzymatically dissociated flexor digitorum brevis (FDB) and soleus fibres from mouse were used to compare the kinetics of electrically elicited Ca2+ transients of slow and fast skeletal muscle fibres, using the fast Ca2+ dye MagFluo4-AM, at 20-22 degrees C. For FDB two Ca2+ transient morphologies, types I (MT-I, 11 fibres, 19%) and II (MT-II, 47 fibres, 81%), were found, the kinetic parameters (amplitude, rise time, half width, decay time, and time constants of decay) being statistically different. For soleus (n = 20) only MT-I was found, with characteristics similar to MT-I from FDB. Correlations with histochemically determined mATPase, reduced nicotinamide adenine dinucleotide diaphorase and alpha-glycerophosphate dehydrogenase activities, as well as immunostaining and myosin heavy chain electrophoretic analysis of both muscles suggest that signals classified as MT-I may correspond to slow type I and fast IIA fibres while those classified as MT-II may correspond to fast IIX/D fibres. The results point to the importance of Ca2+ signaling for characterization of muscle fibres, but also to its possible role in determining fibre function.

Alterations of stiffness and resting position of the elbow joint following flexors resistance training.

Skeletal muscles adapt their length and stiffness according to the functional demands to which they are regularly submitted. The modification of muscle stiffness and length induced by resistance training can alter joint stiffness and, theoretically, change joint resting position. Thirty subjects, randomly assigned to two groups, were submitted to a resistance training of the elbow flexor muscles of the non-dominant arm. This training was performed in the inner range in group 1 and throughout the complete range of motion in group 2. The dominant arm of each subject was considered the control. A biomechanical model of a hybrid mass-spring pendulum was used to estimate the elbow joint stiffness and the elbow resting position was assessed using a standard goniometer. There was a significant increase in joint stiffness of the experimental arm after complete range of motion training, which was not observed after the training performed in inner range. The resting position of the experimental arm was modified to a significantly greater flexion angle in both groups. No change was observed after resistance training in the control arm. The results showed that modifications in joint stiffness seem to depend on the volume of work imposed to skeletal muscles. In addition, both models of resistance training changed, through different mechanisms, the elbow joint resting position. These findings suggest that posture and joint stability may be modified by specific strengthening protocols.

A reduction of tropomyosin limits development of sarcomeric structures in cardiac mutant hearts of the Mexican axolotl.

The cardiac lethal mutation in Mexican axolotl (Ambystoma mexicanum) results in a lack of contractions in the ventricle of mutant embryos. Previous studies have demonstrated that tropomyosin, a component of thin filaments, is greatly reduced in mutant hearts lacking myofibril organization. Confocal microscopy was used to examine the structure and comparative amount of tropomyosin at heartbeat initiation and at a later stage. The formation of functional sarcomeres coincided with contractions in normal hearts at stage 35. A-bands and I-bands were formed at stage 35 and did not change at stage 39. The widening of Z-bodies into z-lines was the main developmental difference between stage 35 and 39 normal hearts. Relative to normal hearts, a reduction of sarcomeric protein levels in mutant hearts at stage 35 was found, and a greater reduction occurred at later stages. The lower level of tropomyosin limited the areas where organized myofibrils formed in the mutant. The areas that had tropomyosin staining also had staining for alpha-actinin and myosin. Early myofibrils formed in these areas but the A-bands and I-bands were shorter than normal. At a later stage in the mutant, A-bands and I-bands remained shorter and importantly the Z-bodies also did not form wider z-lines.

Plasticidad muscular y técnicas de elongación: I parte: bases biológicas del acortamiento / Muscle plasticity and stretching techniques. Part I: biological basis of shortening

En esta serie de dos partes, se revisan y relacionan los aspectos: biomecánicos, neurofisiológicos, morfohistológicos y bioquímicos implicados tanto en el acortamiento como en la elongación muscular. El propósito es determinar y fundamentar, basado en la mejor evidencia disponible, algunos de los parámetros más eficientes para ser aplicados en las Técnicas de Elongación. Para ello se usa como punto de referencia dos métodos: a) el basado en principios de Facilitación Neuromuscular Propioceptiva y b) el Stretching Global Activo, los que difieren en muchas variables. El análisis comparativo se centra en dos: a) el tiempo de mantención del estiramiento y b) la actividad contráctil del músculo a estirar, antes o durante el mismo; las conclusiones se presentarán en la II parte. Esta I parte de enfoca en el fenómeno del acortamiento muscular propiamente tal, concluyéndose que, desde el punto de vista Biomecánico, existen diferencias conceptuales entre cambios a corto plazo (el aumento de la rigidez pasiva) y a largo plazo (disminución de la longitud propiamente tal), que se explican por un comportamiento histológico diferente: lo primero se relaciona con la proliferación de Tejido Conectivo Intramuscular, específicamente perimisio; mientras que lo segundo se debe a una disminución del número de sarcómeros en serie. Esta pérdida de sarcómeros es una expresión de la capacidad plástica del músculo esquelético, para buscar la longitud óptima de cada sarcómero. Se cita además la nueva Hipótesis sobre la propiedad contráctil del perimisio, y su posible rol en el acortamiento.

The positive inotropic effect of angiotensin II: role of endothelin-1 and reactive oxygen species.

Many effects believed to be because of angiotensin II (Ang II) are attributable to the action of endothelin (ET)-1, which is released/produced by Ang II. We investigated whether Ang II elicits its positive inotropic effect (PIE) by the action of endogenous ET-1, in addition to the role played by reactive oxygen species (ROS) in this mechanism. Cat cardiomyocytes were used for: (1) sarcomere shortening measurements; (2) ROS measurements by epifluorescence; (3) immunohistochemical staining for preproET-1, BigET-1, and ET-1; and (4) measurement of preproET-1 mRNA by RT-PCR. Cells were exposed to 1 nmol/L Ang II for 15 minutes. This low concentration of Ang II increases sarcomere shortening by 29.2+/-3.7% (P<0.05). This PIE was abrogated by Na+/H+ exchanger or Na+/Ca2+ exchanger reverse mode inhibition. The production of ROS increased in response to Ang II treatment (DeltaROS respect to control: 68+/-15 fluorescence units; P<0.05). The Ang II-induced PIE and ROS production were blocked by the Ang II type 1 receptor blocker losartan, the nonselective ET-1 receptor blocker TAK044, the selective ETA receptor blocker BQ-123, or the ROS scavenger N-(2-mercapto-propionyl)glycine. Exogenous ET-1 (0.4 nmol/L) induced a similar PIE and increase in ROS production to those caused by Ang II. Immunostaining for preproET-1, BigET-1, and ET-1 was positive in cardiomyocytes. The preproET-1 mRNA abundance increased from 100+/-4.6% in control to 241.9+/-39.9% in Ang II-treated cells (P<0.05). We conclude that the PIE after exposure to 1 nmol/L Ang II is due to endogenous ET-1 acting through the ETA receptor and triggering ROS production, Na+/H+ exchanger stimulation, and Na+/Ca2+ exchanger reverse mode activation.