Fig. 6. Lidocaine reduces cAMP production in a concentration-dependent manner (squares ). This effect was completely abolished by preincubation of Chinese hamster ovary cells with the Gαiinhibitor pertussis toxin (PTX) (X's ), (control vs. PTX [1 μm], *P < 0.001). Addition of the phospodiesterase inhibitor rolipram resulted, as expected, in an increase of cAMP because of its reduced breakdown. However, rolipram did not have any effects on the cAMP-reducing effects of lidocaine nor on the effects of PTX (triangles ).