IMMUNOCYTOCHEMICAL ELECTRON-MICROSCOPIC STUDY AND WESTERN-BLOT-ANALYSIS OF PARAMYOSIN IN DIFFERENT INVERTEBRATE MUSCLE-CELL TYPES OF THE FRUIT-FLY DROSOPHILA-MELANOGASTER, THE EARTHWORM EISENIA-FOETIDA, AND THE SNAIL HELIX-ASPERSA

The presence and distribution pattern of paramyosin have been examined in different invertebrate muscle cell types by means of Western blot analysis and electron microscopy immunogold labelling. The muscles stu died were: transversely striated muscle with continuous Z lines (fligh t muscle from Drosophila melanogaster), transversely striated muscle w ith discontinuous Z lines (heart muscle from the snail Helix aspersa), obliquely striated body wall muscle from the earthworm Eisenia foetid a, and smooth muscles (retractor muscle from the snail and pseudoheart outer muscular layer from the earthworm). Paramyosin-like immunoreact ivity was localized in thick filaments of all muscles studied. Immunog old particle density was similar along the whole thick filament length in insect flight muscle but it predominated in filament tips of fusif orm thick filaments in both snail heart and earthworm body wall muscul ature when these filaments were observed in longitudinal sections. Ln obliquely sectioned thick filaments, immunolabelling was more abundant at the sites where filaments disappeared from the section. These resu lts agree with the notion that paramyosin extended along the whole fil ament length, but that it can only be immunolabelled when it is not co vered by myosin. In all muscles examined, immunolabelling density was lower in cross-sectioned myofilaments than in longitudinally sectioned myofilaments. This suggests that paramyosin does not form a continuou s filament. The results of a semiquantitative analysis of paramyosin-l ike immunoreactivity indicated that it was more abundant in striated t han in smooth muscles, and that, within striated muscles, transversely striated muscles contain more paramyosin than obliquely striated musc les.