Effect of serum and cell density on transmembrane distribution of cAMP and cGMP in transformed (C4-I) and non-transformed (WI-38) human cells.

The ratio between cGMP and cAMP in plasma/urine is elevated in several types of malignancies. The present in vitro study showed that the ratio between extracellular cGMP and cAMP increased during the proliferation of C4-I cells (derived from a carcinoma of the uterine cervix), whereas this ratio decreased in WI-38 cells (normal lung fibroblasts). These results can be explained by differences between the transformed and non-transformed cells in the cell-density-dependent transmembrane distribution and intracellular levels of cyclic nucleotides. In the serum-deprived cultures, no profound effects were seen on the cell-density-dependent biokinetics of cAMP and cGMP. In the absence of serum, growth of C4-I cells was markedly retarded, whereas WI-38 cells were unable to expand at all.