Calcium agonists induce membrane depolarization in endothelial cells through an unknown mechanism. Present studies tested the hypothesis that pulmonary artery endothelial cells express a cyclic nucleotide-gated (CNG) cation channel activated by store-operated calcium entry to produce membrane depolarization. In the whole-cell configuration, voltage-clamped cells revealed a large non-inactivating, outwardly rectifying cationic current in the absence of extra, or intracellular Ca2+ that was reduced upon replenishment of Ca2+. The inward current was non-selective for K+, Na+, Cs+, and Rb+ and was not inhibited by high tetraethylammonium concentrations, cAMP and cGMP stimulated the current and changed the cation permeability to favor Na+. Moreover, 8-bromo-cAMP stimulated the current in voltage-clamped cells in the perforated patch mode. The cationic current was inhibited by the CNG channel blocker LY83,583, and reverse transcriptase- polymerase chain reaction cloning identified expression of a CNG channel resembling that seen in olfactory neurons. Activation of store-operated calcium entry using thapsigargin increased a current through the CNG channel. Stimulation of the current paralleled pulmonary artery endothelial cell membrane depolarization, and both the current and membrane depolarization were abolished using LY83,583. Taken together, these data demonstrate activation of store-operated calcium entry stimulates a CNG channel producing membrane depolarization. Such membrane depolarization may contribute to slow feedback inhibition of store-operated calcium entry.