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The cardiac affects of the purine nucleoside, adenosine, are well known. Adenosine increases coronary blood flow, exerts direct negative chronotropic and dromotropic effects, and exerts indirect anti-adrenergic effects. These effects of adenosine are mediated via the activation of specific G protein-coupled receptors. There is increasing evidence that caveolae play a role in the compartmentalization of receptors and second messengers in the vicinity of the plasma membrane. Several reports demonstrate that G protein-coupled receptors redistribute to caveolae in response to receptor occupation. In this study, we tested the hypothesis that adenosine A 1 receptors would translocate to caveolae in the presence of agonists. Surprisingly, in unstimulated rat cardiac ventricular myocytes, 67 ؎ 5% of adenosine A 1 receptors were isolated with caveolae. However, incubation with the adenosine A 1 receptor agonist 2-chlorocyclopentyladenosine induced the rapid translocation of the A 1 receptors from caveolae into non-caveolae plasma membrane, an effect that was blocked by the adenosine A 1 receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine. An adenosine A 2a receptor agonist did not alter the localization of A 1 receptors to caveolae. These data suggest that the translocation of A 1 receptors out of caveolae and away from compartmentalized signaling molecules may explain why activation of ventricular myocyte A 1 receptors are associated with few direct effects.

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Physical activity is a key component of a healthy lifestyle. Exercise and physical activity have been shown to help maintain a healthy body weight, reduce stress, increase self-esteem and feelings of wellbeing, control blood pressure, and prevent heart disease and diabetes. Children with haemophilia may feel restricted from competing in sports through parental concern or pain and difficulty in moving, or they may rebel against such restrictions, thus leaving themselves open to serious injury. Several groups have attempted to classify sports activities with regard to the level of risk involved; however, these are not consistent. It is important to match the child's abilities with the sport in which they want to take part, and suggest alternatives if this is not possible. Prevention of injury should not depend solely on use of factor concentrates.

Adenosine A2a receptors are found in coronary vascular tissue although, their presence in myocardium is subject to investigation. Although there have been numerous studies on adenosine A2a receptor agonist effects on contractility and cAMP levels in ventricular myocytes, these have yielded conflicting results. Negative pharmacological studies have even led to the conclusion that A2a receptors are not present in cardiac myocytes. The purpose of this study was to determine whether A2a receptors are expressed in rat ventricular myocytes and what physiological effects are mediated via activation of these receptors. Western blot analysis with a polyclonal antibody raised against a peptide sequence specific to the carboxy terminus of the A2a receptor revealed the presence of a band at approximately 45 kDa. However, the immunoreactivity was located in the nonmembrane fraction of the cell lysate. The membrane fraction only exhibited an immunoreactive band > or = 50 kDa. Treatment of isolated myocytes with the adenosine A2a agonist 2-[4-[(2-carboxyethyl)-phenyl]ethylamino]-5'-N-ethylcarboxamidoadenosine (CGS-21680) exerted no effects on cAMP levels or myocyte twitch amplitude. These results indicate that although rat ventricular myocytes appear to express adenosine A2a receptors, stimulation with an A2a agonist exerts no functional effects, possibly because of the subcellular localization of the A2a receptor.