SMOOTH-MUSCLE ACTIN AND MYOSIN EXPRESSION IN CULTURED AIRWAY SMOOTH-MUSCLE CELLS

In this study, the expression of smooth muscle actin and myosin was ex amined in cultures of rat tracheal smooth muscle cells. Protein and mR NA analyses demonstrated that these cells express alpha- and gamma-smo oth muscle actin and smooth muscle myosin and nonmuscle myosin-B heavy chains. The expression of the smooth muscle specific actin and myosin isoforms was regulated in the same direction when growth conditions w ere changed. Thus, at confluency in 1 or 10% serum-containing medium a s well as for low-density cells (50-60% confluent) deprived of serum, the expression of the smooth muscle forms of actin and myosin was rela tively high. Conversely, in rapidly proliferating cultures at low dens ity in 10% serum, smooth muscle contractile protein expression was low . The expression of nonmuscle myosin-B mRNA and protein was more stabl e and was upregulated only to a small degree in growing cells. Our res ults provide new insight into the molecular basis of differentiation a nd contractile function in airway smooth muscle cells.