INTRACELLULAR-DISTRIBUTION OF IRON (AND ASSOCIATED ELEMENTS) IN VARIOUS CELL-TYPES OF LARVAE AND JUVENILES OF THE SEA LAMPREY (PETROMYSOM MARINUS)

The intracellular distribution of iron and other elements was examined in various cell types in larvae and juveniles of the sea lamprey (Pet romyzon marinus) using transmission electron microscopy and energy dis persive x-ray microanalysis. The objective was to establish whether th ere are cell-type specific relationships beween iron and other element s in the iron-rich organs and tissues (adipose tissue, opisthonephric kidneys, dorsal integument, fat column, liver, and posterior intestine ) of these two life cycle periods. Iron was localized within either de nse bodies (presumptive lysosomes, siderosomes) or in the cytoplasmic matrix of many cell types where it was viewed as haemosiderin/ferritin and ferritin, respectively. Presumptive lysosomes of adipocytes of th e nephric folds, dorsal integument, and fat column possessed iron and sulphur and this elemental association was also prevalent in the epith elia of the larval proximal tubules and in the posterior intestine and epidermis of both life periods. Macrophages of the larval haemopoieti c tissue (posterior intestine) and of the juvenile opisthonephros, whi ch were described as melanomacrophages because of their granules, poss essed iron, sulphur, and calcium. This elemental association was also noted in the presumptive lysosomes of the iron-loaded hepatocytes of t he juvenile liver while no elements could be detected in these cells i n the larval organ. The variations and similarities in elemental assoc iations between the cell types in each life period and at different li fe periods is discussed in the context of specific cell functions rela ted to the prevention of iron toxicity. These functions are sequestrat ion of iron and storage as the less toxic haemosiderin (larval adipocy tes, macrophages, juvenile hepatocytes) or as part of a process of eli mination of excesses of this metal (posterior intestine, dorsal epider mal cells). Due to its unique ability to deal with copious amounts of iron at all periods of the life cycle, the lamprey serves as an import ant model for studies of iron loading in vertebrates.