**6. Reversibility of VSMCs between the contractile and synthetic phenotypes**

When VSMCs cultured in honeycombs are treated with collagenase-I and the released cells are seeded in plastic plates, they start to proliferate again [5]. This result shows the remarkable plasticity of VSMCs. The relationship between the culture system and phenotypic modulation is shown in Figure 8.

Filamin A mRNA expression is almost identical in VSMCs cultured in honeycombs and on plates, and VSMCs moved to plates mainly express the 280-kDa form of filamin after 12 h [5]. These observations indicate that filamin might contribute to the phenotypic modulation seen in VSMCs.

**Figure 8.** Summary of VSMC phenotypic modulation in culture. These images are scanning electron microscopic obser‐ vations. Arrowheads show VSMCs and arrows show honeycombs. VSMCs cultured on plates express the synthetic phenotype. This type of VSMC is de-differentiated and can proliferate. VSMCs cultured in honeycombs display similar features to the contractile phenotype. These two phenotypes are reversible depending on the type of culture used. These photographs were taken from reference 4 to make it easy to understand the culture system.

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bars, 20 µm (A, C); 5 µm (B, D). Data adapted from reference 5.

µm (A, C); 5 µm (B, D). Data adapted from reference 5.

452 Muscle Cell and Tissue

 Figure 7. Localization of filamin and β-actin in VSMCs. (A, B) VSMCs were cultured to subconfluence on a plate. (C, D) VSMCs were cultured in honeycombs for 3 days. Green indicates filamin, and red indicates β-actin. Scale

When myocardial cells derived from newborn rats are cultured in honeycombs, the cells attach to the honeycombs and start beating from the first day. The rate of beating increases gradually,

**Figure 7.** Localization of filamin and β-actin in VSMCs. (A, B) VSMCs were cultured to subconfluence on a plate. (C, D) VSMCs were cultured in honeycombs for 3 days. Green indicates filamin, and red indicates β-actin. Scale bars, 20
