Figure 3.

Effect of N⁶-cyclopentyladenosine (CPA) on Forskolin-stimulated cyclic AMP accumulation in guinea-pig tracheal epithelial cells. Cells were preincubated 15 min in the presence of Rolipram (10 μM) and adenosine deaminase (1.5 u·ml⁻¹) and thereafter stimulated for 5 min in the absence (Control) or in the presence of 10 μM forskolin alone (Forskolin) or with forskolin and increasing concentrations of CPA (+CPA). Values are the mean±s.e.mean of four determinations made with different cell preparations, expressed as percentage of the response to 10 μM forskolin. ^*P<0.05 and ^**P<0.01.