Smooth muscle proteins as intracellular components of the chromatophores of the Antarctic fishes Pagothenia borchgrevinki and Trematomus bernacchii (Nototheniidae)

Melanophores, xanthophores, and iridophores from the skins of the two Antar ctic fish species Pagothenia borchgrevinki and Trematomus bernacchii were t ested immunocytochemically for the presence of a variety of muscle proteins . Actin, myosin, and calmodulin, not surprisingly, were confirmed for all t hree chromatophore types of the two fishes, but the presence of caldesmon a nd calponin, both characteristic proteins of smooth muscle fibers, represen ts a new discovery. It is not known at this stage whether these proteins oc cur also in the chromatophores of other fishes and are not restricted to An tarctic species. Since, however, motility control of particles in fish chro matophores and the regulation of smooth muscle tension both involve the sym pathetic nervous system, the presence of similar target proteins should not come as a surprise. The fact that none of the chromatophores tested positi ve for troponin shows that there is no close relationship between pigment c ells and striated muscle. The lack of alpha-actinin in iridophores, but its presence in melanophores and xanthophores, is thought to be a reflection o f the considerably greater pigment translocations within the latter two typ es of chroinatophore cells.