270sol tyrosine hydroxylase activities and melanin biosynthesis. These changes did not occur in control cultures carried on in parallel in the standard medium. In soft agar, melanotic and amelanotic melanoma cells produce 2 major morphologically distinct types of colonies. The 2 major colony variants were: a) groups of 50-250 dark (melanotic) small (5-20 gm diameter) cells, and b) groups of 5-50 light, large (20-40 Ixm diameter) cells. Control cultures in standard DMEM maintained their dark small morphology for over 30 subcultures. On the other hand, on the 3rd subculture, each of the experimental cultures, i.e. cultures grown in media supplemented with either M-THI inhibitor or L-DOPA, gave a mixture of the 2 types of colonies, and on the 7th subculture they gave mostly the light, large colonies. Human melanoma cells contain 2 types of endogeneous tyrosine hydroxylase (TH) inhibitors. By filtration through Amicon membranes, the data in table 2 indicate that the inhibitors differed in molecular size. The M-THI inhibitor from supernatants of the cloned hybrids had the highest Experientia 38 (1982), Birkh~iuser Verlag, CH-4010 Basel/Switzerland molecular weight. All the 3 inhibitors are protein in nature, but only M-THI in presence of the enzyme produced a precipitin band in agar suggesting that it is an antibody to tyrosine hydroxylase. Whilst the method in somatic hybridization, introduced by K6hler and Milstein 2~ has proved entirely successful for the production of antibodies against particulate antigens such as those on the cell surface 21'22 and viruses 23, it has only recently been successfully applied to soluble tumor markers such as CEA 2, hCG 25 and alpha-fetoprotein 26. Inhibition of tyrosinase activity produces regression of abnormal cell growth in human and mouse melanoma 27-29.The described experiments showed the binding of estrogen to tyrosine hydroxylase present in cytosols of melanotic melanoma cells, thus confirming reports by other investigators 17'18. They also demonstrated the production of an enzyme inhibitor by somatic cell hybrids. The role of these inhibitors in the modulation of melanin biosynthesis, differentiation, morphology and oncogenicity of human malignant melanoma are under current studies.Summary. In adrenaline cells, junctional complexes formed by alternating gap junctions and attachment plaques were identified in close proximity to bilateral clusters of mitochondria. It is suggested that this proximity is related to a role of gap junctions in metabolic coupling.Gap junctions have been structurally identified between contacting cells of most tissues especially glandular epithelia. Only recently, however, freeze-fracture studies have revealed the presence of gap junctions in the adrenal medulla 1. Gap junctional particle aggregates were shown to be relatively scarce, with many linear and loop-like configurations. The possibility existed therefore that adrenomedullary cells might possess small and non-macular gap junctions previously missed in studies of thin sections, revealing on...
