HEL-37 cells rapidly transferred microinjected fluorescein between contacting cells. This transfer was strongly inhibited by tumor-promoting phorbol esters and mezerein but not by nonpromoting derivatives. The onset of the inhibition occurred after 5 to 10 min of exposure to the test compound and was complete within 20 min. Using a wash-of procedure, it was demonstrated that inhibition of dye transfer by phorbol-12,13-dibutyrate was fully reversed by 100 min, after a lag of 40 to 60 min. The recovery of dye transfer competence was blocked by puromycin. Both 12-O-tetradecanoylphorbol-13-acetate and monensin caused elevated Na+ levels in HEL-37 cells, but the latter compound did not inhibit dye transfer. It was concluded that the promoter inhibition of transfer was not a consequence of Na+-induced increase in cytoplasmic Ca2+ concentration.
This study was supported by the Australian Research Grants Committee, the National Health and Medical Research Council, and the Universities of South Australia Anti-Cancer Foundation.