title: A comparative analysis of intermediate filament proteins in bovine heart Purkinje fibres and gastric smooth muscle.
abstract: The intermediate filament (IF) composition of muscle cells of various sources is still a controversial issue. In the present study, the IF composition of bovine Purkinje fibres (PFs), atrial and ventricular myocardium, and gastric smooth muscle (SM) has been compared using biochemical and immunocytochemical methods. The Mr of the major IF subunit protein in all four tissues was 55,000. In two-dimensional (2-D) electrophoresis gels of Triton-treated ordinary atrial and ventricular myocardium and the gastric muscular wall, two or three isoelectric isoforms were seen, whereas in PFs up to seven isoforms caused by phosphorylation were observed. In immunofluorescence studies antibodies against the Mr 55,000 subunit of PFs and gastric SM, respectively, both showed identical reactivity with PFs, atrial and ventricular myocytes, gastric SM cells and some SM cells in intramyocardial and gastric muscular wall blood vessels. A small amount of vimentin (Mr 57,000) was also detected in 2-D gel electrophoresis in all four tissues as well as in immunoblotting of PFs with antibodies to vimentin. Immunofluorescence studies using both polyclonal and monoclonal antibodies to vimentin showed that vimentin was present in the endothelium and SM cells of both intramyocardial and gastric muscular wall vessels, sometimes together with desmin in the vascular SM cells, but was never seen in PF, atrial, ventricular or gastric SM cells proper. As expected, vimentin was present in interstitial tissue, i.e., fibroblasts and capillaries. However, interestingly, the monoclonal antibodies, which recognized different antigenic determinants of vimentin, did not give identical staining patterns. Especially the staining of the vascular SM cells differed. Since this staining pattern did not change upon denaturation and unmasking experiments, it seems that the organization of vimentin in different mesenchymal cell types varies. Vimentin was also detected in isolated PFs but here it was located solely in the contaminating interstitial tissue. Thus, desmin is the sole IF protein expressed in PFs, in atrial and ventricular myocytes and in gastric SM cells proper; vimentin alone being present in the interstitial tissue cells, whilst in vascular SM cells desmin and vimentin are coexpressed in various proportions. The variation in number of isoforms of desmin and the heterogeneity in staining of mesenchymal tissues with monoclonal vimentin antibodies probably indicates that the IF cytoskeletons are differently organized in various cell types, even though they contain IFs of the same class.
mesh_terms: D000818:Animals; D002417:Cattle; D004591:Electrophoresis, Polyacrylamide Gel; D004797:Enzyme-Linked Immunosorbent Assay; D006329:Heart Conduction System / Q000032:analysis*; D007381:Intermediate Filament Proteins / Q000032:analysis*; D008970:Molecular Weight; D009130:Muscle, Smooth / Q000032:analysis* / Q000166:cytology; D009928:Organ Specificity; D011690:Purkinje Fibers / Q000032:analysis* / Q000166:cytology; D013270:Stomach / Q000032:analysis* / Q000166:cytology
chemical_list: D007381:Intermediate Filament Proteins