PRESENCE OF ALPHA-SMOOTH ACTIN IN PRIMITIVE BONY FISH SMOOTH-MUSCLE

alpha-smooth muscle (alpha SM) actin of endothermic vertebrates is sel ectively recognized by the monoclonal antibody anti-alpha SM-1. Using anti-alpha SM-1, the presence of alpha SM actin was recently detected in smooth muscle cells of ectothermic tetrapods and of the elasmobranc h shark. We have now investigated the anti-alpha SM-1 immunoreactivity in vascular and visceral smooth muscle of bony fishes. Three ray-finn ed bony fishes, the polypteriform Calamoichthys calabaricus and two te leost members, Anguilla anguilla and Carassius auratus, and one lobe-f inned bony fish, the lungfish Protopterus annectens were screened. The results demonstrated that smooth muscle of both teleosts tested did n ot immunoreact with anti-alpha SM-1, while a strong immunoreactivity w as detected in smooth muscle of both Calamoichthys and Protopterus. In addition the submucosa myofibroblasts were also labelled. The present results confirm that this isoform evolved early in vertebrate lineage .