[en] The tissue distribution of injected ⁶⁵Zn in mice with Harding-Passey or B-16 melanomas was studied. Both types of melanoma took up remarkably large amounts of ⁶⁵Zn (Harding-Passey 17.4%; and B-16 almost 26.0% of the ⁶⁵Zn dose administered). In the case of the B-16 melanoma, the tumor was the dominant site of incorporation even in terms of specific activity. On the subcellular level, melanosomes isolated by gradient ultracentrifugation were shown to be the sites of preferred deposition of ⁶⁵Zn. The high uptake of ⁶⁵Zn by melanomas and its specific binding by melanosomes suggests that this isotope might be useful in detecting melanomas. (author)

[en] Studies of transport across the plasma membrane in intact cells frequently involve measuring the incorporation of a labelled extracellular species into the cells. Unfortunately, if the labelled species is metabolized in the cell, the kinetics of labelling are made more complicated. Using the example of the incorporation of ³²P-labelled orthophosphate into cells, we describe a mathematical model which allows for this complication, and show how this may alter the interpretation of experiments. The anlysis is widely applicable to cellular labelling studies with any species that undergoes chemical exchange with a large cellular pool. (author)

[en] Small doses (1 to 10 μg daily) of 24,25-dihydroxycholecalciferol (24,25-(OH)₂D₃), a renal metabolite of vitamin D of uncertain function, increased intestinal absorption of calcium in normal people and in patients with various disorders of mineral metabolism, including anephric subjects. In five of six patients studied, calcium balance increased, but, unlike 1,25-dihydroxycholecalciferol, 24,25-(OH)₂D₃ did not increase plasma or urinary calcium concentrations. These results suggest that 24,25-(OH)₂D₃ may be an important regulator of skeletal metabolism in man with potential value as a therapeutic agent. (author)