Fig. 2. Reduction of vascular smooth muscle myosin expression in the coronary arteries of Cx431 knockout hearts. Transverse sections of neonatal mouse hearts stained with anti-vascular smooth muscle myosin antibody. (A,B) As the coronary artery exits the aorta (LCA), the coronary artery stem and its mouth (double-headed arrow) are greatly reduced in the Cx431^–/– (B) versus wild-type (A) heart. Ao, aorta; PI, pulmonary infundibulum (right ventricular outflow tract); RCA, right coronary artery; LCA, left coronary artery. (C,D) A reduction in vascular smooth muscle myosin expression in large branches of the right and left coronary arteries (BrRCA or BrLCA) of the Cx431^–/– (D) versus wild-type (C) heart. (E-J) A similar reduction in smooth muscle labeling is seen in the mural arteries of the right (E,F) and left ventricular walls (I,J), and in arteries of the ventricular septum (G,H). (E,G,I) Wild-type vessels; (F,H, J) Cx431^–/– vessels. Note the reduction in size of the Cx431 knockout vessels and the interruption of vascular smooth muscle myosin immunolabeling in the walls of the Cx431 knockout vessels.