Figure 6. Inhibition of CNP fragment-induced cGMP production in CEPI-17-CL4 cells by two NP receptor antagonists is shown. The effects of HS-142–1 (10 nM to 10 µM; closed square symbols) and isatin (0.3–100 µM; open circle symbols) on CNP fragment (30 nM)-induced cGMP generation were determined as described in the methods section. Data are mean±SEM from 6 to 7 experiments for HS-142–1, and from 7 experiments for isatin. Similar results were obtained using p-CEPI cells. The antagonist potencies of the two compounds in the two cell-types are provided in the Results section.