Microphotometric determination of enzyme activities in type-grouped fibres of reinnervated rat muscle.

Activities of succinate dehydrogenase (SDH), glycerolphosphate oxidase (GP-OX), cytochrome oxidase (CYT-OX) and lactate dehydrogenase (LDH) were determined microphotometrically in single, actomyosin-ATPase typed ( Guth and Samaha 1970) fibres within cross-sections of normal and reinnervated rat tibialis anterior muscles. SDH and GP-OX activities displayed pronounced scattering and large overlaps existed between alpha-, alpha beta-, and beta-fibres of normal muscle. Coefficients of variation were in the range of 16-40% for GP-OX and SDH in the different fibre populations. Enzyme activity determinations in type-grouped alpha-, alpha beta-, and beta-fibres of reinnervated muscle showed much less scattering than in normally distributed alpha-, alpha beta-, and beta-fibres of control muscles. Coefficients of variation were in the range of 10-13% for SDH, GP-OX, CYT-OX and LDH. The experimental error of the kinetic microphotometric measurement of enzyme activities in situ is in the range of 10% ( Reichmann and Pette 1982). Our results therefore suggest a high degree of metabolic similarity or homogeneity of typed-grouped muscle fibres and thus support the assumption that type-grouped fibres are homogeneous and correspond to regularly assembled motor units.