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The transformed or normal phenotype of cultured normal rat kidney cells infected with a temperature-sensitive mutant of avian sarcoma virus is conditional on the temperature at which the cells are grown . Using dye injection techniques, we show that junction-mediated dye transfer is also temperature-sensitive . The extent and rate of transfer between infected cells grown at the transformation-permissive temperature (35°C) is significantly reduced when compared to infected cells grown at the nonpermissive temperature (40.5°C) or uninfected cells grown at either temperature . Infected cells subjected to reciprocal temperature shifts express rapid and reversible alterations of dye transfer capacities, with responses evident by 15 min and completed by 60 min for temperature shifts in either direction . These results suggest that altered junctional capacities may be fundamental to the expression of the ASV-induced, transformed phenotype .

Spontaneously transformed and virallytransformed cells are restored to contact-inhibited growth by the addition of dibutyryl cyclic AMP to the nutrient medium. Theophylline, an inhibitor of the phosphodiesterase that degrades cyclic nucleotides, must also be present for maximal effect. Once the transformed cells reach a saturation density in the presence of the additives, release from the contact-inhibited state occurs upon removal of the dibutyryl cyclic AMP and theophylline from the medium. Agglutinability of the transformed cells by wheat-germ agglutinin (a monitor of architectural changes in the plasma membrane) is decreased by dibutyryl cyclic AMP-theophylline treatment, but increases again upon removal of the additives.

The adenosine 3',5'-monophosphate (cyclic AMP) levels of mouse lymphocytes rose and fell sharply 10 hours after stimulation with concanavalin A. Treatment of the cells with indomethacin reversibly prevented the increase in cyclic AMP and the subsequent onset of DNA synthesis. When the heightened cyclic AMP before S phase was maintained by either inhibiting phosphodiesterase or by adding the 8-bromo derivative of cyclic AMP, DNA synthesis was also blocked. Both the increase and decrease in cyclic AMP appear to be required for progression of lymphocytes into the S phase of growth.