Smooth muscle cells of the chicken aortic arch differ from those in the gizzard and the femoral artery in the distribution of F-actin, alpha-actinin and filamin.

The distribution of F-actin, alpha-actinin and filamin in smooth muscle cells of the chicken was examined by immunofluorescent and immunoelectron microscopy. Those from the gizzard, the femoral artery and the aortic arch were compared. F-Actin labeled by NBD-phallacidin was seen diffusely distributed in the sarcoplasm in the gizzard and the femoral artery, but in the aorta it was observed as streaks and spots, with unstained areas in between. Epon sections of the aortic arch showed that bundles of thin myofilaments run in various directions interspersed with areas mostly occupied by intermediate filaments. alpha-Actinin labelling occurred in dense plaques along the sarcolemma in all the muscles examined. While dense bodies in the sarcoplasm were common and labelled for alpha-actinin in the gizzard and the femoral artery, hardly any were seen in the aortic arch and little labelling for alpha-actinin was observed in the sarcoplasm. Filamin was concentrated along the periphery of dense bodies and plaques in the gizzard and the femoral artery, but it was seen diffusely in the sarcoplasm of the aortic muscle. After chemical skinning of the latter, filamin labelling persisted only in the F-actin bundles, and other areas became negative. The present results show that smooth muscle cells of the aortic arch contrast with those of the gizzard and even with those of the femoral artery in the distribution of F-actin, alpha-actinin and filamin. The mechanisms of contraction and/or stress maintenance in the aortic smooth muscle may be different from those in other smooth muscles.