Endothelin-1 Alters the Contractile Phenotype of Cultured Embryonic Smooth Muscle Cells

Abstract Smooth muscle tissues may be classified into phasic (fast) or tonic (slow) contractile phenotypes. This study was initiated to examine the specification of these phenotypes during development and the role of growth factors in this process. We used myosin light chain 17 (MLC17) and myosin heavy chain transcript splice variants as markers of the tonic (aortic) and phasic (intestinal) smooth muscle phenotypes in chick embryos. By reverse transcription–polymerase chain reaction, we determined embryonic days 6 to 16 to be a critical period for the establishment of these phenotypes. During this period, endothelin-1 is present at 40-fold-higher levels in aortic compared with intestinal tissues. To test the hypothesis that endothelin-1 may be involved in establishing the aortic (tonic) phenotype, we developed a system in which embryonic smooth muscle cells exhibit phasic and tonic contractile properties in vitro. Single-cell force measurements showed that cultured embryonic gizzard (phasic) cells develop...