An immune histochemical and enzymic characterization of the muscle fibres in myotomal muscle of the teleost Brachydanio rerio, Hamilton-Buchanan.

The myotomal muscles of teleosts have a complex internal structure. For a better understanding of the functional anatomy of these muscles we analysed the myofibrillar properties of the myotomal muscle fibres in a small teleost: Brachydanio rerio, the zebrafish. By immune histochemical techniques we discerned 4 types of muscle fibres: red lateral fibres, red muscle rim (RMR) fibres, intermediate fibres and white fibres, each with a distinct type of heavy chain myosin. In addition we discerned 2 populations of muscle fibres in which the myofibrils contain mixtures of white and intermediate heavy chain myosin. The immune histochemical classification correlates well with an enzyme histochemical classification of the muscle fibres. In order to find out whether the immune and enzyme histochemical differences correlate with differences in dynamic properties of the muscle fibres, we analysed the ATP-ase activity of glycerinated muscle fibres. 3 of the 5 muscle fibre types which are discriminated by immune histochemical methods could thus be analysed. Differences in histochemical reactions coincide with differences in ATP-ase activities of the glycerinated muscle fibres. 2 classes of muscle fibres were homogeneous as to the ATP-ase activity of their muscle fibres. The 3rd class, the white fibres, could be divided in 2 populations with slightly different ATP-ase activities. The results indicate that the myotomal muscle fibre population is much more heterogeneous than has been considered thusfar. This heterogeneity may allow an almost continuous range of contraction speeds in the myotomal muscle.