Titin: structure, isoforms and functional regulation / 生理学报

Titin, the largest known protein in the body expressed in three isoforms (N2A, N2BA and N2B), is essential for muscle structure, force generation, conduction and regulation. Since the 1950s, muscle contraction mechanisms have been explained by the sliding filament theory involving thin and thick muscle filaments, while the contribution of cytoskeleton in force generation and conduction was ignored. With the discovery of insoluble protein residues and large molecular weight proteins in muscle fibers, the third myofilament, titin, has been identified and attracted a lot of interests. The development of single molecule mechanics and gene sequencing technology further contributed to the extensive studies on the arrangement, structure, elastic properties and components of titin in sarcomere. Therefore, this paper reviews the structure, isforms classification, elastic function and regulatory factors of titin, to provide better understanding of titin.

Efeitos da corrida em esteira em músculos sóleos de ratos encurtados por imobilização / Effects of running on treadmill in soleus muscles of rats shortened by immobilization

O objetivo deste trabalho foi verificar as adaptações de peso e comprimento do músculo sóleo de ratos Wistar machos, além da estimativa do total de sarcômeros em série e comprimento médio dos sarcômeros, quando submetidos a um processo de remobilização em esteira. Foram utilizados 18 ratos (Wistar), divididos em três grupos: GC - músculo sóleo esquerdo (MSE) imobilizado e remobilizado solto; G10 - MSE imobilizado e remobilizado em velocidade de 10m/min; e G12 (n = 6) - MSE imobilizado e remobilizado em velocidade de 12m/min. Os resultados mostraram as seguintes variações, peso muscular: GC -22,35 por cento (p = 0,0089), G10 -12,52 por cento (p = 0,0623), G12 -12,07 por cento, (p = 0,0004); comprimento muscular: GC -5,47 por cento (p = 0,0120), G10 -3,31 por cento (p = 0,2868), G12 0,41 por cento (p = 0,8987); estimativa de sarcômeros em série: GC -15,42 por cento (p = 0,0047), G10 -10,87 por cento (p = 0,0193), G12 -4,97 (p = 0,2409); comprimento de sarcômeros GC 11,16 por cento (p = 0,0142), G10 9,31 por cento (p = 0,1270), G12 5,58 por cento (p = 0,1327). Conclui-se que G12 obteve maior eficácia após o período de imobilização, pois apresentou maior semelhança com o membro não imobilizado.

The aim of this work was to compare weight and length adaptations of the soleus muscle of male Wistar rats as well as estimation of the total number of serial sarcomere and mean sarcomere length, when they are submitted to remobilization on treadmill. 18 Wistar male rats were used and divided in the three following groups: CG - left soleus (LS) muscle immobilized and remobilized free in the cage; G10 - LS muscle immobilized and remobilized in speed of 10 m/min on treadmill; and G12 - LS muscle immobilized and remobilized in speed of 12 m/min. The right muscles (RS) of each animal were used for comparison. The results showed the following variations, muscular weigh: CG -22.35 percent (p = 0.0089), G10 -12.52 percent (p = 0.0623), G12 -12.07 percent, (p = 0.0004); muscle length: CG -5.47 percent (p = 0.0120), G10 -3.31 percent (p = 0.2868), G12 0.41 percent (p = 0.8987); estimation of number of serial sarcomere: CG -15.42 percent (p = 0.0047), G10 -10.87 percent (p = 0.0193), G12 -4.97 (p = 0.2409); sarcomere length: CG 11.16 percent, (p = 0.0142), G10 9.31 percent (p = 0.1270), G12 5.58 percent (p = 0.1327). It was concluded that G12 presented the best effectiveness after immobilization period since it presented greater similarity with the non-immobilized soleus.