Muscles of fishes are active in a variety of movements that differ in velocity, duration and excursion length. To investigate how muscles meet the, often conflicting, demands imposed upon them by these movements, the fibre type composition of several muscles was determined. The ultrastructural and contractile properties of some of the obtained fibre types were measured and compared with their functional activity.<br/>In head muscles as well as in body muscles of perch and carp, four types of muscle fibres were distinguished on the basis of reactions with antisera and on the pH stability of myosin ATPase. In both fishes, two fast types (white and pink) and two slow types, (red a and red b in the carp and red and deep red in the perch) were found (chapter I and chapterIII). In the perch both slow types could be divided into subtypes on the basis of the activity of enzymes of the aerobic and anaerobic metabolism (chapter I).<br/>In the perch, a muscle part consisting of red fibres, showed electromyographic activity during slow, continually repeated movements (respiration). Another part of the same muscle, containing white and pink fibres, only showed activity during fast vigorous movements (cough, suction feeding on prey) (chapter I).<br/>To investigate the morphological basis for functional differences between the fibre types, quantitative ultrastructural studies were made. In both fishes, the four fibre types differed in the extent of contact between the T system and the sarcoplasmic reticulum (T-SR contact). White fibres had the most extensive T-SR contact, red b fibres (in the carp) and deep red fibres (in the perch) had the least extensive T-SR contact (chapter II and chapter V).<br/>Slow as well as fast muscle fibres of perch and carp are multiply innervated. Slow fibres of the carp have a higher density of nerve terminations than fast fibres (chapter III).<br/>The contractile properties of small bundles of pink- and red muscle fibres of the carp were measured in a nerve-muscle preparation (chapter IV). Contractile properties of white-,pink-and deep red fibres of the perch were obtained from small fibre bundles stimulated by means of long electrodes, parallel to the fibre axis (chapter VI). All investigated types reacted to a single stimulus with a twitch. Time to peak tensions increased in the order: white fibres (perch), pink fibres (perch and carp), red fibres (a mixture of the types red a and b of the carp) and deep red fibres (perch). The extent of contact between<br/>the T system and the sarcoplasmic reticulum decreased in the same order (chapter VI, fig. 5). 1<br/>The position of the T system (at the level of the Z line or at the junction between A band and I band) was not related to the extent of contact between the T system and the sarcoplasmic reticulum, as was expected from earlier qualitative studies. In muscle fibres of the perch, this position appeared to be related to the length of the actin filaments. Differences in sarcomere length- tension curves, predicted on the basis of differences in actin filament length in a sliding filament- cross bridge model (chapter II), were confirmed by experimental results (chapter VII).<br/>Fast- and slow fibre bundles have similar maximal tetanic tensions per unit cross sectional area, although slow fibres have a lower relative volume of myofibrils (chapter IV and VI).<br/>Red fibres of the carp have a beter endurance than pink fibres, as was measured by repeated tetanisation (chapter IV). This is in agreement with their higher relative volume of mitochondria and amount of glycogen (chapter V).<br/>The results from this study show that fibre types present in the same muscle may differ in contraction velocity, sarcomere lengthtension curve and endurance. This indicates that each fibre type is suitable to a different activity, as is indeed confirmed by their different electromyographic activity.<br/>The obtained knowledge of the histochemical and structural characteristics of different fibre types and their functional meaning will provide a useful tool for further investigation, especially of development and growth of fish muscle.
|Qualification||Doctor of Philosophy|
|Award date||5 Oct 1984|
|Place of Publication||Wageningen|
|Publication status||Published - 1984|
- muscle tissue