Force-length properties in stable skeletal muscle fibers - Theoretical considerations
JOURNAL OF BIOMECHANICS
Authors: Allinger, TL; Herzog, W; Epstein, M
Differences in the force-length (F-L) properties between sarcomeres and fibers have been associated with the supposed unstable nature of the sarcomere F-L relation on the descending limb (i.e. at sarcomere lengths greater than optimal length). Recently, it has been suggested that sarcomere behavior in a fiber is stable during contractions on the descending limb of the F-L relation; therefore, a factor other than sarcomere instability must be responsible for the observed differences in the F-L relation of sarcomeres and fibers. The purpose of this study was to determine theoretically the F-L relation of a muscle fiber when sarcomeres were at a stable, steady-state length. Three models of muscle fibers are presented; each model contains sarcomeres with different mechanical properties which have been observed experimentally. Results of these theoretical considerations demonstrate that sarcomeres with the classic F-L properties as measured by Gordon et al. (J. Physiol. 184, 170-192, 1966) cannot predict the F-L relation exhibited by fibers. The addition of cross-bridge stiffness properties to the classic sarcomere F-L relation still does not explain the differences between the sarcomere and fiber F-L relations. However, if history dependent sarcomere properties are used, the fiber F-L relation exhibits an elongated plateau and greater forces on the descending limb compared to the classic sarcomere F-L relation; and the fiber F-L relation corresponds qualitatively to experimental findings. Copyright (C) 1996 Elsevier Science Ltd.
Infection-induced autoantibodies and pregnancy related pathology: an animal model
REPRODUCTION FERTILITY AND DEVELOPMENT
Authors: Petrusic, Vladimir; Zivkovic, Irena; Muhandes, Lina; Dimitrijevic, Rajna; Stojanovic, Marijana; Dimitrijevic, Ljiljana
In addition to being the main cause of mortality worldwide, bacterial and viral infections can be the cause of autoimmune and pregnancy disorders as well. The production of autoantibodies during infection can be explained by various mechanisms, including molecular mimicry, bystander cell activation and epitope spreading. Conversely, bacterial and viral infections during pregnancy are especially dangerous for the fetus. It is documented that infection-induced inflammatory processes mediated by Toll-like receptors (TLR) represent the main cause of preterm labour. We used two crucial bacterial components and TLR ligands, namely peptidoglycan and lipopolysaccharide, to stimulate BALB/c mice before immunisation with tetanus toxoid. Tetanus toxoid is an inactive form of the toxin produced by bacterium Clostridium tetani and shares structural similarity with plasma protein beta(2)-glycoprotein I. Treatment with peptidoglycan and lipopolysaccharide in combination with tetanus toxoid induced the production of pathological autoantibodies, different fluctuations in natural autoantibodies and different types of reproductive pathology in treated animals, with peptidoglycan treatment being more deleterious. We propose that the production of pathological autoantibodies, TLR activation and changes in natural autoantibodies play crucial roles in infection-induced reproductive pathology in our animal model.