Fig. 3.
Evidence for phosphodiesterase activation. A, left, reduction of cellular cAMP by 20 μM CNTinh-03 in response to 0.01 μM isoproterenol (in β2 receptor-expressing CHO cells). Cells were incubated with agonists/CNTinh-03 for 20 min before assay. Propranolol was used at 20 μM. Middle, cAMP stimulated by 10 μM forskolin in CHO cells. Right, cAMP stimulated by 3 h incubation with 1 μg/ml cholera toxin (CTX). Data are mean ± S.E. (n = 3-5). B, reduction of cellular cGMP by CNTinh-03 in response to 45-min incubation with 0.15 μg/ml STa toxin (SE, n = 4). C, IBMX abrogates cAMP suppression by CNTinh-03, showing cellular cAMP in the absence and presence of 20 μM CNTinh-03 / 100 μM IBMX as indicated. D, CNTinh-03 inhibition of short-circuit current (Isc) in basolateral membrane-permeabilized FRT cells expressing human CFTR. As indicated, cells were incubated with 10 μM CNTinh-03 (or DMSO vehicle), followed by addition of 20 μM cAMP or 8 μM CPT-cAMP in the basolateral (bl) bathing solution. E, experiments done as in D, except for pretreatment with 50 μM dipyridamole (or DMSO vehicle) before addition of 10 μM CNTinh-03 (or DMSO vehicle), followed by 20 μM cAMP in the basolateral bathing solution. Experiments in D and E are representative of three similar sets of measurements.