SMOOTH-MUSCLE MYOSIN REGULATION BY SERUM AND CELL-DENSITY IN CULTUREDRAT LUNG CONNECTIVE-TISSUE CELLS

Smooth muscle myosin regulation by serum and cell density in cultured rat lung connective tissue cells. Am. J. Physiol. 265 (Lung Cell. Mol. Physiol. 9): L127-L132, 1993.-RNA and protein analyses were used to d etect expression of SM1 and SM2 smooth muscle myosin heavy chain (MHC) in cultured adult rat lung connective tissue cells (RL-90). Smooth mu scle MHC mRNA expression in confluent cells grown in 10% serum was app roximately 50% of the level in adult stomach. Similar results were obt ained in cells cultured at low density (25% confluency) in 1% serum. H owever, in low-density cultures transferred to 10% serum for 24 h, the level of MHC mRNA decreased to approximately 20% of that in adult sto mach. Smooth muscle alpha-actin showed a pattern of expression similar to that for smooth muscle MHC. Expression of nonmuscle MHC-A mRNA was higher in all culture conditions compared to stomach. MHC-A mRNA expr ession was less in low-density cultures in low serum and increased whe n low-density cultures were transferred to 10% serum for 24 h. MHC-B m RNA expression was less in low- vs. high-density cultures. In contrast to MHC-A, however, MHC-B mRNA expression in low-density cultures was higher in low serum. Immunofluorescence and immunoblotting with SM1-sp ecific antibody demonstrated the presence of the SM1 protein isoform a s well as reactivity to a protein band migrating slightly faster than SM2. These results demonstrate that cultured rat lung connective tissu e cells express smooth muscle MHC and that expression is modulated by culture conditions.