Quantitative immunohistochemistry of parvalbumin expression in the rat diaphragm

Parvalbumin is a calcium-binding protein involved in the mechanism of Ca++ exchange between sarcoplasmic reticulum and the myofibrils. This characteristic promotes a direct correlation between the amount of parvalbumin and the velocity of contraction-relaxation of skeletal muscle fibers. To quantify the expression of parvalbumin in the rat diaphragm, transverse paraffin sections of this muscle were processed immunohistochemically using antiparvalbumin monoclonal antibody. The stained sections were inspected on an image analysis device to evaluate the intensity of the immunoreaction and to make morphologic measurements of the muscle fibers. The immunoreaction intensity data allowed the division of fibers in fast- and slow-twitch types. The rat diaphragm was characterized as a fast-twitch muscle due to the presence of 59.8% of fast-twitch fibers. The fibers' lesser diameter values showed that the slow-twitch fibers had a small diameter as compared to the fast-twitch ones (P < .001). The method used suggests that immunohistochemistry for parvalbumin assisted by image analysis is a feasible technique to separate fast- and slow-twitch skeletal muscle fibers in paraffin sections and to characterize their morphologic profiles.