FIBER TYPES IN LEECH BODY WALL MUSCLE

The fibre type composition of obliquely striated muscle of adult Hirudo medicinalis was investigated by enzyme histochemistry, by immunohistochemistry and by SDS-PAGE. The oxidative capacity of the fibres, assessed by succinate dehydrogenase activity, was similar in all three layers of body wall muscle (longitudinal, oblique and circular) and in dorsoventral muscles. Histochemical localisation of Mg2+-activated actomyosin ATPase activity gave stronger staining in the longitudinal muscle than in other layers. As muscle shortening speed is directly related to this form of ATPase activity, this suggests that the longitudinal layer fibres are faster contracting than the circular, oblique or dorsoventral muscles. Results with polyclonal antibodies specific for vertebrate myosins were consistent with the ATPase results, i.e. fibres with the lowest actomyosin ATPase activity reacted preferentially with an antibody for a slower myosin. Thus, anti-T2, selective for vertebrate tonic fibre myosin, bound preferentially to fibres in oblique, circular and dorsoventral muscles, whereas anti-S, selective for vertebrate slow twitch fibre myosin (faster than vertebrate tonic fibre myosin), bound preferentially to the bulk of longitudinal layer fibres. Whereas most of the longitudinal layer stained uniformly with the anti-S antibody, some fibres in the outermost bundles were negative for the anti-S antibody and were, therefore, different from the main mass of longitudinal fibres. SDS-PAGE analysis of contractile protein preparations from body wall muscle also revealed a difference in the composition of the oblique, circular and dorsoventral muscles compared to the longitudinal layer, supporting the conclusion that leech body wall muscle contains two fibre types.