HISTOCHEMICAL AND IMMUNOHISTOCHEMICAL STUDIES ON THE ORIGIN OF THE BLUE MARLIN HEATER CELL PHENOTYPE

The superior rectus muscle fibers of marlins, swordfish, sailfish and spearfish are modified for heat production at the expense of contracti le ability, Although 'heater cells' are a muscle derivative (Block, 19 86, 1991), the myoblast origin and developmental pathway of these ther mogenic cells is unknown, To gain insight into heater cell origins, we characterized blue marlin superior rectus muscle and its heater tissu e derivative with histochemical and immunological techniques, We speci fically employed myosin ATPase and succinate dehydrogenase histochemic al assays, and myosin heavy chain immunohistochemistry. Results reveal ed that marlin superior rectus muscles contain at least six distinct f iber types, and suggested the presence of both twitch and tonic fibers . Immunological results indicate that myosin is present within the the rmogenic cells but not in myofibrillar lattices, The antibodies that r ecognized myosin in heater cells also labeled myosin in the twitch fib ers of swimming muscle, In contrast, antibodies that labeled histologi cally defined tonic fibers did not label heater cells. These results s uggest that heater cells and twitch fibers express the same myosin iso form, and establish a phenotypic connection between heater cells and t witch fibers. This conclusion is discussed in the context of the muscl e-to-heater trajectory and the muscle fiber-type origin of heater cell s.