Figure 2.

(a) Measurement of mesenchymal cell elongation caused by different uniaxial stretching forces. Undifferentiated (round) cells were measured in this study. Each column represents the mean maximal diameter of 50 cells ± SD. (b) RT-PCR shows induction of SM-specific mRNA in undifferentiated embryonic lung mesenchymal cells after 2 hours of 5% uniaxial stretch. (c) Immunoblot shows SM α-actin translation in embryonic lung mesenchymal cells after 18 hours of uniaxial stretch. (d) Lack of myogenic response to stretch in undifferentiated mesenchymal cells from the intestine and kidney after 2 hours of uniaxial stretch are shown. This study was done under conditions that inhibit cell proliferation (1% FBS). (e) Immunoblots show stretch-induced upregulation of SM-specific protein synthesis in embryonic mesenchymal cells undergoing spread-induced myogenic differentiation. Notice that desmin requires more time to be stimulated. The cells are plated under conditions that allow cell spreading and then stretched for 2, 6, or 24 hours (lanes 2 and 3). The nonstretched controls (lane 1) were cultured for 24 hours. (f) Upon reaching full SM differentiation (96 hours in culture, SM-specific protein levels and electrical properties of mature SM cells; ref. 11), mesenchymal cells stop responding to stretch under the conditions tested here. The studies presented in b–f were repeated more than three times with similar results.