Ion Fluxes through KCa2 (SK) and Cav1 (L-type) Channels Contribute to Chronoselectivity of Adenosine A1 Receptor-Mediated Actions in Spontaneously Beating Rat Atria.

Impulse generation in supraventricular tissue is inhibited by adenosine and acetylcholine via the activation of A1 and M2 receptors coupled to inwardly rectifying GIRK/KIR3.1/3.4 channels, respectively. Unlike M2 receptors, bradycardia produced by A1 receptors activation predominates over negative inotropy. Such difference suggests that other ion currents may contribute to adenosine chronoselectivity. In isolated spontaneously beating rat atria, blockade of KCa2/SK channels with apamin and Cav1 (L-type) channels with nifedipine or verapamil, sensitized atria to the negative inotropic action of the A1 agonist, R-PIA, without affecting the nucleoside negative chronotropy. Patch-clamp experiments in the whole-cell configuration mode demonstrate that adenosine, via A1 receptors, activates the inwardly-rectifying GIRK/KIR3.1/KIR3.4 current resulting in hyperpolarization of atrial cardiomyocytes, which may slow down heart rate. Conversely, the nucleoside inactivates a small conductance Ca(2+)-activated KCa2/SK outward current, which eventually reduces the repolarizing force and thereby prolong action potentials duration and Ca(2+) influx into cardiomyocytes. Immunolocalization studies showed that differences in A1 receptors distribution between the sinoatrial node and surrounding cardiomyocytes do not afford a rationale for adenosine chronoselectivity. Immunolabelling of KIR3.1, KCa2.2, KCa2.3, and Cav1 was also observed throughout the right atrium. Functional data indicate that while both A1 and M2 receptors favor the opening of GIRK/KIR3.1/3.4 channels modulating atrial chronotropy, A1 receptors may additionally restrain KCa2/SK activation thereby compensating atrial inotropic depression by increasing the time available for Ca(2+) influx through Cav1 (L-type) channels.

Aspectos fisiológicos do envelhecimento / Physiological aspects of ageing

Envelhecimento é um fenômeno de grande complexidade e variabilidade, com dimensões biológicas, sociais e psicológicas, sendo um processo contínuo em que ocorrem alterações irreversíveis ao longo da vida. O declínio do organismo é caracterizado pela redução das capacidades dos sistemas orgânicos, contudo, não é possível determinar o exato momento em que a velhice começa a se manifestar. É fato que a forma como a pessoa envelhece está relacionada ao seu estilo de vida e a maneira como encara este processo.

Efecto del entrenamiento de fuerza sobre la autonomía funcional en mujeres mayores sanas / Effects of a strength training program on functional status in healthy elderly women

Objetivo: evaluar el efecto de un programa de entrenamiento de fuerza durante 20 semanas sobre la autonomía funcional de mujeres mayores saludables. Material y métodos: participaron 24 mujeres mayores de 65 años divididas en grupo experimental (GE; n = 13) y grupo control (GC; n = 11). El GE fue sometido a 20 semanas de intervención constituida por 2 fases de entrenamiento: extensión de rodillas, supino en posición sentada, tirón en la polea, flexión unilateral de rodillas, flexión parcial de tronco (abdominal), trabajo de bíceps y tríceps en la polea. Se determinó la autonomía funcional mediante una batería de pruebas incluidas en el protocolo GDLAM antes del ejercicio y en la 4.a y 20.a semana. Se compararon los resultados mediante ANOVA multivariada para medidas repetidas, siguiendo la prueba post hoc de Tukey para muestras desiguales, adoptando un nivel de significación estadística p 5,86; p < 0,005, respectivamente) en relación al GC. Conclusión: la realización de entrenamiento de fuerza durante 20 semanas muestra una mejora en la autonomía funcional para realización de las actividades de la vida diaria en mujeres mayores sanas. Cabe indicar ejercicio específico en grupos seleccionados de población mayor con riesgo de pérdida de autonomía

Objective: to evaluate the effect of a 20-week strength training program on functional status in healthy elderly women. Material and methods: twenty-four women aged more than 65 years old participated in this study. The women were divided into an experimental group (EG, n = 13) and a control group (CG, n = 11). The EG underwent a 20-week intervention consisting of two training phases: knee extension, supine in a sitting position, machine lat pull-down, unilateral knee flexion, partial flexion of the trunk (abdominal), and biceps curl and triceps extension against resistance. Functional status was determined through a battery of tests included in the GDLAM protocol before exercise and at weeks 4 and 20. The results were compared through multivariate repeated measures ANOVA, with the post-hoc Tukey test for unequal samples. Statistical significance was set at p 5.86; p < 0.005, respectively) in comparison with the CG. Conclusion: The 20-week strength training program improved functional autonomy in activities of daily living in healthy elderly women. Specific exercises should be indicated in selected groups of the elderly population at risk of loss of autonomy