Inhibition of proliferation in H69 cells by the β-adrenergic agonist isoproterenol and the GIRK channel inhibitor U50488H. H69 cells were grown in the presence of isoproterenol or U50488H or a combination of Iso and U5 for 48 hours. Proliferation was determined by a BrdU assay. Both 10 μM Iso (p < 0.001) and 2 μM U5 (p < 0.001) inhibited proliferation with Iso having the greater effect. The effect of the GIRK inhibitor U5 on proliferation was potentiated by Iso (p < 0.001). N = 5.