Ultrastructure of microtubules in dermal melanophores and spinal nerve of the Antarctic teleost Pagothenia borchgrevinki

Summary The antarctic teleost, Pagothenia borchgrevinki inhabits the Antarctic Ocean where the water temperature remains around -1.9° C throughout the year. Dermal melanophores of this fish respond within minutes to epinephrine and theophylline with melanosome aggregation and dispersion, respectively. Numerous cytoplasmic microtubules are present in these cells despite the low environmental temperature. In longitudinal profiles, many microtubules are twisted, beaded and sometimes even branched. In cross sections, C-, U-, S-, 6- and other irregularly shaped tubules are observed. Nocodazole partially disrupts microtubules and inhibits epinephrine-induced pigment aggregation. Pigment movements are also prevented by erythro-9-[3-(2-hydroxynonyl)] adenine. Although the participation of these incomplete microtubules in cell motility remains uncertain, the results indicate that this fish has a cold-resistant microtubule system on which melanosome movements depend. Unlike those in melanophores, microtubules in the axons of spinal nerves are of uniform thickness and often contain an electron-dense core in the center.