DIFFERENTIAL PROCESSES OF VASCULAR SMOOTH-MUSCLE CELL-DIFFERENTIATIONWITHIN ELASTIC AND MUSCULAR ARTERIES OF RATS AND RABBITS - AN IMMUNOFLUORESCENCE STUDY OF DESMIN AND VIMENTIN DISTRIBUTION

Two main populations of smooth muscle cells exist in the arterial medi a of adult mammals with respect to expression of two intermediate fila ment proteins: vimentin-positive/desmin-negative cells (V+/D-) and vim entin-positive/desmin-positive ones (V+/D+). However, it is still not understood how this phenotypic diversity is established. Since the pro portion and the distribution patterns of the two muscle cell populatio ns depend both on the type of blood vessel and the species examined, t he aim of the present study was to determine and to compare their deve lopmental origin in various artery segments from two different species . Using confocal scanning laser microscopy and sections stained by mea ns of immunofluorescence, the distribution patterns of desmin and vime ntin were compared in transverse sections of thoracic and abdominal ao rtas (elastic arteries) and of the femoral artery (muscular artery) of newborn and adult rats (n = 12) and rabbits (n = 12). The comparison of sections labelled with specific antibodies showed the existence of a subpopulation of smooth muscle cells in the aortas, but not in the f emoral artery, which expressed desmin in newborns but not in adults. T hese data suggest that the phenotype of smooth muscle cells in elastic arteries but not in muscular arteries is modulated during development .