Amlodipine increases nitric oxide synthesis in cytokine-stimulated cultured vascular smooth muscle cells

Objective If calcium channel blockers affect nitric oxide synthesis in the vascular tissue, they could influence disease progression in coronary arteries. We investigated the effects of the calcium channel blocker amlodipine on nitric oxide synthesis by measuring the production of nitrite, a stable metabolite of nitric oxide, in vascular smooth muscle cells. Methods We measured the production of nitrate in cultured rat vascular smooth muscle cells with the Griess reagent Inducible nitric oxide synthase protein and mRNA expression were assayed by Western blotting and reverse transcription-polymerase chain reaction, respectively. The levels of NF-κB proteins in nuclear extracts were analyzed by gel retardation assay. Results Incubation of cultures with interleukin-1 β (10 ng/ ml) for 24 h caused a significant increase in nitrite generation. Interleukin-1 β-induced nitrite production by vascular smooth muscle cells was significantly increased by amlodipine in a dose-dependent manner. This augmentative effect of amlodipine was completely abolished in the presence of N G -monomethyl-L-arginine or actinomycin D. Amlodipine-induced nitrite production was accompanied by increased inducible nitric oxide synthase mRNA and protein accumulation. Interleukin-1 β induced NF-κB activation in vascular smooth muscle cells, and addition of amlodipine further increased this NF-κB activation. The effect of amlodipine on nitrite production was maintained in the presence of the calcium channel agonist Bay K 8644. Conclusion Amlodipine enhances nitric oxide synthesis in cytokine-stimulated cultured vascular smooth muscle cells by L-type calcium channel-independent mechanisms.