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(Circulation Research. 2005;96:890.)
© 2005 American Heart Association, Inc.

Integrative Physiology

Contractile Properties of the Cultured Vascular Smooth Muscle Cells

The Crucial Role Played by RhoA in the Regulation of Contractility

Dan Bi, Junji Nishimura, Naohisa Niiro, Katsuya Hirano, Hideo Kanaide

From the Division of Molecular Cardiology, Research Institute of Angiocardiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.

Correspondence to Hideo Kanaide, MD, PhD, Prof, 3-1-1 Maidashi, Fukuoka, 812-8582, Japan. E-mail kanaide{at}molcar.med.kyushu-u.ac.jp

Vascular smooth muscle cells (VSMCs) have a remarkable degree of plasticity and in response to vascular injury, they can change to a dedifferentiated state that can be typically seen in cell cultures. Recently, Y27632, a Rho kinase inhibitor, has been reported to preferentially correct hypertension in a hypertensive rat model. We thus tested the hypothesis that the contraction of the cultured VSMCs might be more dependent on the function of RhoA than the VSMCs in fresh tissue. For this purpose, a tissue-like ring preparation was made using the cultured porcine coronary artery SMCs (CASMCs) and collagen gel (reconstituted ring: R-ring). The R-ring developed an isometric tension on stimulation by high external K⁺ or various receptor agonists. The phorbol ester (a protein kinase C (PKC) activator)-induced contraction of the intact R-ring was greatly inhibited, while the GTPS (an activator of RhoA)-induced and Ca²⁺-independent contraction of permeabilized R-ring was greatly enhanced, in comparison to the fresh coronary artery ring. An immunoblot analysis showed the expression levels of RhoA and myosin phosphatase subunits (MYPT1 and PP1c) to be up-regulated, while the levels of CPI-17 (PKC-potentiated protein phosphatase-1 inhibitory protein), h1-calponin and PKC isoforms were downregulated in cultured CASMCs. The knock down of RhoA by RNA interference decreased the contractility of the cultured CASMCs. It is concluded that the contractility of the cultured VSMCs thus appears to be much more dependent on the function of RhoA than VSMCs in fresh tissue. The expression level of RhoA thus plays a crucial role in regulating the contractility of cultured VSMCs.

Key Words: vascular smooth muscle • contraction • RhoA • CPI-17 • RNA interference • vascular disease

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