Evidence for novel 30,000-50,000Mr cofactor in the activation of muscle

A new approach is described for reconstituting a fully desensitized skeletal muscle fiber to restore its contractility. These studies revealed a novel regulatory cofactor, 30-50,000Mr by filtration (26-55kDa by SDS PAGE). It was shown to be critical for the Ca2+-activation in the physiological milieu. The cofactor was present in skeletal and cardiac muscles as well as in brain, but not in kidney and liver. The cofactor may be a second Ca2+ switch in a dual-regulation scheme for vertebrate muscle, or could provide an essential link in the cross-bridge cycle beyond activation.     

Age-Sex Analysis of Activity Budget,Diet, and Positional Behavior in <Emphasis Type="Italic">Alouatta caraya</Emphasis> in an Orchard Forest

Howlers (Alouatta spp.) spend more than half of the daytime resting and their diet consists predominantly of leaves. Associated with a general strategy of energy conservation, their positional behavior is characterized by quadrupedalism as the major locomotor mode, and sitting as the most common resting and feeding posture. However, researchers have sparse information on the degree to which age-sex classes fit the generic trends and the influence of habitat structure on them. We compare the activity budget, dietary composition, and positional behavior by age-sex or age classes in a group of black-and-gold howlers (Alouatta caraya) in a small orchard forest. We collected 26,474 behavioral records via instantaneous scan sampling over 1 yr. The main activity was resting (56%) and the diet comprised mainly leaves (82%); sitting was the most adopted feeding (61%) and resting (52%) posture, and walking was the most prevalent locomotor mode (38%). There are age-sex differences for all major behaviors. Whereas resting tended to increase with body size, moving decreased. We observed no difference in the consumption of major plant parts. There were ontogenetic differences in most positional behaviors. Sitting increased from infants to adults during feeding, whereas the opposite occurred for bridging and hanging. During resting, infants curled more and lay less than the other classes did, whereas adults engaged in more sitting. Adults and subadults walked more than individuals of other ages did; infants climbed and bridged more than others did; and, there were opposing trends in leaping and descending. Habitat structure is a partial explanation of the locomotor behavior of black-and-gold howlers.