The relation of endogenous adenosine cyclic 3′:5′‐monophosphate to the antagonistic effects of adenosine and colchicine on cell shape

Adenosine and colchicine have antagonistic effects on cell shape. When Chinese Hamster lung fibroblasts (CHE36‐6) or SV40 transformed 3T3 (SV3T3) cells are incubated with colchicine (1 μM) for one hour at 37°C, they round up into spheres with short spikes. Cells treated with adenosine (1 μM–4 mM) for one hour become refractile and develop spindly processes. However, when the two compounds are added simultaneously, the characteristic responses to either drug are abolished and the cells appear normal. The counteraction is specific for adenine and its derivatives, adenosine being the most effective of the compounds we tested. Accumulation of colchicine or adenosine is not altered significantly by the presence of the other drug, ruling out decreases in uptake as the basis of the mutual antagonism. The morphological changes can be observed under conditions where there are no changes in intracellular cAMP levels (such as incubation with low concentrations of adenosine or cordycepin, an adenosine analog that cannot be directly converted to cAMP). Colchicine does not alter cAMP content of control or adenosine‐treated cells. These data show that adenine compounds have potent effects on cell shape, and the antagonistic effects of adenosine and colchicine on cell shape are not mediated through changes in intracellular cAMP levels.