We have utilized [3H]diacetyl-didemnin B ([3H]DB) in a series of in vitro experiments to determine the time course of equilibration of [3H]DB between plasma and blood cells, the distribution of [3H]DB among blood cells, and the distribution of [3H]DB in plasma. Within 45-60 min at 37 degrees C, approximately 55% of [3H]DB added to whole blood remained in the plasma. Of the drug associated with blood cells, 77% was found with the red blood cells, 18% with the lymphocytes, and 5% with the granulocytes. However, on the basis of amount of drug uptake per cell, lymphocytes incorporated nearly 400 times more and granulocytes nearly 30 times more [3H]DB than red blood cells. No specific association of [3H]DB with a particular lymphocyte subset was detected. Additionally, it appears that [3H]DB in plasma was associated to a large extent with albumin.

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Rat pheochromocytoma PC12 cells have been treated with nerve growth factor (NGF) at final concentrations of 2, 4, 8, and 16 ng/ml, and then were exposed to 60-Hz, sinusoidal magnetic fields (MF) of 12.5, 25, 50, and 100 microT (rms) for 30 min. Transcript levels for both c-fos and glyceraldehyde-3 -phosphate dehydrogenase were determined by Northern blot analysis using 32P-labeled cDNA probes. No change in c-fos expression was measured at any condition employed. Treatment of PC12 cells with a combination of agents (NGF, forskolin, and tetradecanoylphorbol acetate [TPA]) increased c-fos expression over that detected with NGF alone. MF exposure of cells treated with the three-agent regimen produced two outcomes, either no change or a doubling of c-fos expression. In subsequent experiments, cells were treated with NGF, NGF + forskolin + TPA, or pre-treated with anisomycin and then treated with NGF + forskolin + TPA. It was determined that MF exposure, like superinduction with anisomycin, increased c-fos expression only in cultures which were not yet exhibiting maximal c-fos expression. It is hypothesized that MF exposure, like anisomycin, may alter the activity of key intracellular protein kinases.