12th Ljudevit Jurak International Symposium on
Comparative Pathology
June 1-2, 2001

V. Groma, V. Zalcmane, A. Kazanceva, A. Skagers, G. Salms
Medical Academy of Latvia, Riga, Latvia
Abstract: The myoepithelial cells are found in all the salivary glands of the oral cavity. These cells are located between the glandular epithelial cells, small intralobular ductal epithelial cells, and the basal lamina. These are basket-like cells with a flattened body and long cytoplasmic processes, which surround the terminal secretory portions and assist in the discharge of secretion. The myoepithelial cells bear dual epithelial/myogenic cytological characteristics. The contractile proteins, namely alpha-smooth muscle actin, myosin, calponin and desmin, are located in the cell processes and are responsible for the myogenic phenotype of these cells. This study aimed to demonstrate the myoepithelial cells expression in the case of vascular ligation (facial and/or carotid) using immunolabelling for different muscle-specific proteins, to clarify a contribution of the myoepithelium to the investigated events; to select the most suitable immunohistochemical marker for the evaluation of changes occurring in the muscular phenotype of the myoepithelial cells in the case of experimental conditions designed in this study; and to estimate a volume fraction of the myoepithelium using a morphometrical approach, and the dynamic changes of this fraction under exposure to the above mentioned experimental conditions. The submandibular and the parotid glands of  rabbits after a long-term facial and/or carotid ligation were removed, fixed in formalin, embedded in paraffin, and thereafter processed for immunohistochemistry (with the muscle-specific monoclonal antibodies: alpha-smooth muscle actin, calponin and desmin) using the ABC-immunoperoxidase method. In a controled enviroment periacinar and periductal myoepithelial cells demonstrated diffusion but no prominent immunostaining by monoclonal antibodies to the alpha-smooth muscle actin and calponin, whereas immunostaining with an antibody to intermediate cytoskeletal protein desmin was almost nil. Acinar and ductal epithelial cells were entirely negative. In the case of vessel ligation the myoepithelial cells revealed only occasional desmin expression. The contractile muscular phenotype demonstrated by the actin and calponin expression was more prominent comparing with the desmin. The actin expression showed especially strong immunoreactivity. A tight network of the myoepithelial cells heavily stained with the anti-actin antibody was interspersed between the secretory and the ductal portions of the glands of the experimental animals. The visual density of this network was much more prominent than in the control group. Since the actin expression was believed to be the most reliable immunohistochemical marker for  myoepithelial changes analyzed in this study, the slides stained with the anti-actin antibody were used for morphometrical estimation. The volume fraction was calculated using point-counting method. The other fractions calculated included serous acinar, tubular acinar, intralobular ductal, connective tissue septal, adipose tissue as well as vascular fractions. It was detected that the volume fraction of the myoepithelium in the experimental animals was 2 and more times greater than in the control group, and this finding correlates with a decrease of the acinar and an increase of the septal fractions. It was suggested that the myoepithelial cells containing heterogeneous contractile and cytoskeletal proteins actively participate in the pathological events designed in the present study; the muscle-specific proteins  reflect the changes along the experiment differently; the alpha-smooth muscle actin is a very suitable immunohistochemical marker; the morphometrical approach is superior when compared with a number of other subjective estimations and widely used semiquantitative scores.  
Poster Presentation