HepG2 or SK-N-MC cells were detached by treatment with phosphate-buffered saline-EDTA, resuspended and incubated for 15 min at 37°C in 200 μl of Hepes-buffered DMEM containing either vehicle (basal), 1 μM forskolin or 1 μM forskolin plus 10 μM UK14304. Concentrations of cAMP were measured as described in “Materials and Methods.” Results are expressed as picomoles of cAMP per milligram of cellular protein and are means ± S.E. of 18 determinations. Statistical analysis was performed using the Student’s ttest.

• * P < .001, significant inhibition of forskolin-stimulated cAMP production.