Theophylline plus dibutyryl 3′,5′-cyclic adenosine monophosphate (dibutyryl cAMP) decreases the multiplication rate of both BHK21C13 and BHK21Py cells. The level of saturation density of BHK21C13 cultures is diminished in the presence of theophylline plus dibutyryl cAMP. On the contrary, dibutyryl cAMP plus theophylline does not prevent BHK21Py cultures from reaching the high saturation density observed in the absence of nucleotide.

Dibutyryl cAMP plus theophylline or dibutyryl cAMP alone inhibit both phosphate transport and metabolism in normal as well as in transformed cells, but the mean phosphate uptake is more inhibited in BHK21C13 cells than in BHK21Py cells. The results agree with the hypothesis that 3′,5′-cyclic adenosine monophosphate is an intermediate in the contact inhibition of growth.

This content is only available via PDF.