Parvalbumin expression in the diaphragm of aged rats

Parvalbumin is a calcium-binding protein involved in the mechanism of Ca(++) exchange between the sarcoplasmic reticulum and the myofibrils. There is a direct correlation between the amount of parvalbumin and the velocity of contraction-relaxation of skeletal muscle fibers. Male Donryu rats (6, 24 and 30 months of age) were housed in a specific pathogen free room and fed with 60% of the mean daily quantity of rodent chow consumed by rats fed ad libitum. To assess the expression of parvalbumin in the rat diaphragm, transversal sections were processed immunohistochemically using polyclonal antiparvalbumin antibody. The stained sections were inspected on an image analysis device to evaluate the intensity of the immunoreaction and to take morphological measurements of the muscle fibers. The optical density data allowed the distinction of fibers in fast- and slow-twitch types. The results show that the number of fibers did not change in young and old rats, but the percentage of muscle fibers containing parvalbumin decreased with age. Moreover, the fast-twitch fibers showed a remarkable decrease in their diameter at 30 months of age, but the slow-twitch ones did not. The results suggest that, as the organism gets old, the fiber type composition of the diaphragm changes to adapt to different physiological and/or metabolic exigencies.