Role of cyclic 3':5'-adenosine monophosphate in the early transport changes induced by serum and insulin in quiescent fibroblasts.

Serum or insulin added to quiescent mouse-embryo fibroblasts produced rapid increases in the rate of transport of uridine and phosphate and a decrease of the intracellular concentration of cyclic AMP. Incubation of the cells with prostaglandin E(1), theophylline, or both prevented the increase in uridine transport produced by serum or insulin. Prostaglandin E(1) was more effective than prostaglandins E(2) and B(1). Kinetic experiments showed that the addition of prostaglandin E(1) and theophylline causes the uridine transport rate to return to the basal level within 5 min; the rate rose rapidly after their removal. Similar effects were obtained when insulin was used instead of serum. Associated with these transport changes were significant variations in the levels of cyclic AMP. An inverse correlation between the changes in uridine transport and those in cyclic AMP concentration was shown under various experimental conditions. In contrast to the effects observed with uridine transport, phosphate uptake was only slightly affected by changes in the endogenous level of cyclic AMP. We propose that at least two different sorts of membrane changes are rapidly initiated by serum, one under cyclic AMP control and the other not related to this nucleotide.