The effect of some experimental parameters on the inhibition of metabolic cooperation by phorbol myristate acetate.

The effect of cell density, PMA exposure time, concentration, pre-exposure and binding activity on the recovery of V 79 HGPRT- Chinese hamster cells in the metabolic cooperation assay was determined. A PMA exposure interval of only 1 min resulted in maximum recovery of HGPRT- cells. PMA began to inhibit metabolic cooperation at a dose as low as 0.1 ng/ml final media concentration. The recovery of HGPRT- cells varied according to cell density in the presence or absence of PMA, although the magnitude of this effect was much greater in untreated cells. Pre-exposure of cells to PMA increased the recovery of both post-PMA-treated and non-treated HGPRT- cells in a dose-dependent manner. [3H]PMA was rapidly bound to or taken up by V 79 cells. These results suggest that the inhibitory effect of PMA on metabolic cooperation in V 79 cells involves receptor binding.