Effect of stretch on growth and collagen synthesis in cultured rat and lamb pulmonary arterial smooth muscle cells.

There are no studies of the effect of stretch in cultured pulmonary vascular smooth muscle, and some data suggest that a stretch-mediated increase in connective tissue synthesis in pulmonary arteries is mediated by the endothelium. To investigate whether stretch can serve as a growth stimulus in this smooth muscle, we studied two types of cultured pulmonary arterial smooth muscle cells (a multiply passaged clonal line of rat cells [PAC1], and early passage lamb cells [EPTC]). Cells were grown on a collagen-coated silicone surface and subjected to repetitive stretch (0.33-0.5 Hz; 10-20% strain). The relative rates of total RNA, DNA, protein, and soluble collagen synthesis were determined using 3H precursors, and c-fos and collagen mRNAs by Northern blot analysis. Stretch caused no significant change in the rate of RNA synthesis in either PAC1 cells (+9%) or EPTC (-3%). The relative rate of total protein synthesis was decreased by stretch (6% in PAC1 cells and 36% in EPTC [both NS]) as was the rate of collagen synthesis (-24% in EPTC [NS]). In EPTC, the percentage of 3H-thymidine labeled cells was modestly increased with 24 h stretch (17 +/- 5.7%; P < .001), but trichloroacetic acid (TCA) precipitated 3H-thymidine was unaltered by stretch, and the number of cells not significantly changed with stretch. c-fos mRNA expression was only inconsistently induced by stretch x 30 min in EPTC, and not at all in PAC1 cells. Expression of mRNA for alpha 1 (I) and alpha 1 (III) collagen was not changed significantly by 24 h or 48 h of stretch. We conclude that stretch does not serve as a significant growth stimulus in cultured pulmonary vascular smooth muscle cells in this system. These findings do not rule out the possibility that stretch is a growth stimulus for these cells under different conditions, but do suggest that other models will be needed to determine if and how mechanical stimuli affect growth of pulmonary vascular smooth muscle.