RESUMEN
Prolonged bed rest, undertaken by volunteers or resulting from injury and disease, can impair bone and muscle function and structure; extended travel in space also induces these effects. Fluid shifts and disrupted fluid balance may also contribute to observed musculoskeletal aberrations in the weightless environment. Some molecular and cellular events involved in the loading and unloading of the musculoskeletal system are under neural and endocrine influence or control, whereas other events are influenced by local growth factors. Studies are in progress to develop interventions that preserve or improve musculoskeletal integrity in 1g. The NIAMS and NASA are interested in basic and clinical studies of the influence of microgravity on the musculoskeletal system. The interagency workshop results form the basis for new collaborative and cooperative research emphases for the biomedical community under a broad agreement between the National Institutes of Health and NASA.
Asunto(s)
Huesos/fisiología , Músculos/fisiología , Vuelo Espacial , Agencias Gubernamentales , Humanos , National Institutes of Health (U.S.) , Estados UnidosAsunto(s)
Actomiosina , Adenosina Trifosfatasas , Miosinas , Adenosina Difosfato , Adenosina Trifosfato , Calcio , Fluorescencia , Hidrólisis , Cinética , Magnesio , Modelos Químicos , Isótopos de Oxígeno , Fosfatos , Potasio , Protones , AguaRESUMEN
The characteristic equatorial X-ray pattern from a relaxed vertebrate skeletal muscle changes when the muscle is activated. In particular, there is a simultaneous decrease in the intensity of the first reflection (I10) and increase in the intensity of the second (I11). This observed change is almost reciprocal. When compared with the predictions of computer modeling, it produces a strong argument that the intensity change is due to a redistribution of myosin heads (myosin subfragment-1 or S-1), which results from the formation and configuration changes of actin-myosin links. Computer modeling shows that different actin-S-1 configurations will give different numerical values for I10 and I11, assuming the same number of attachments. For a given configuration, the intensity changes are a nonlinear function of attachment number, so that direct scaling of force to reflection intensity may be difficult. Data from active muscle are consistent with the notion that in different states of active muscle, i.e. shortening or isometric, there are different average configurations of actin-myosin attachment and different numbers of actin-myosin links.
Asunto(s)
Actinas/metabolismo , Miosinas/metabolismo , Fragmentos de Péptidos/metabolismo , Unión Proteica , Conformación Proteica , Difracción de Rayos XAsunto(s)
Músculos/ultraestructura , Animales , Anuros , Microscopía Electrónica , Rana pipiens , Difracción de Rayos XRESUMEN
Low angle x-ray diffraction patterns were obtained from resting and activated frog sartorius muscles by means of a position-sensitive detector. Although the intensity ratio I10/I11 decreased many-fold upon activation, it was nearly the same during isometric and isotonic contraction. Thus, motion has a much smaller effect on the low order equatorial pattern than the transition from rest to activity. Analysis of the 10 and 11 reflections separately showed that I10 and I11 change reciprocally upon activation, and that they both increase by a small amount in the transition from isometric to isotonic contraction. If the intensity ratio can be taken as a measure of cross-bridge number, the results provide evidence that the drop in force in an actively shortening muscle is due primarily to the influence of motion on the configuration, rather than the number, of cross-bridges.