Comparison of levels of gene induction in wild-type cells and act15cAR cells. act15cAR1, act15cAR2, act15cAR3, and wild-type AX3 cells were first stimulated for 6 h with 30 nM (act15cAR1, act15cAR3, and AX3) or 600 nM (act15cAR2) cAMP pulses, washed, and subsequently incubated for 0 or 8 h in the presence and absence of 300 μM cAMP per h. mRNA was isolated and hybridized to CP2 and psA cDNAs. The experiment was repeated once with similar results.