Recombinant HEK293 cell line expressing human PDE1B (phosphodiesterase 1B, accession number NM_000924). ; N-terminal His-tagged human PDE1B has been stably expressed in HEK293 cell line and its expression was confirmed by Western blotting. The function of PDE1B was characterized by a cell-based cGMP assay. In this assay system, cells co-express atrial natriuretic peptide (ANP) receptor A (a guanylate cyclase), cyclic nucleotide5gated cation channel CNGA2, and the photoprotein aequorin. Intracellular cGMP level is monitored via aequorin luminescence induced by Ca2+ influx through CNGA2, acting as the intracellular cGMP sensor.