Role of transient receptor potential C3 in TNF-α-enhanced calcium influx in human airway myocytes

Previous studies have suggested that the proinflammatory cytokine, TNF-α, contributes to airway hyperresponsivness by altering airway smooth muscle (ASM) Ca²⁺ responses to agonist stimulation. The present study examined the effects of TNF-α on Ca²⁺ influx pathways in cultured human ASM cells (HASMCs). Proteins encoded by the transient receptor potential (TRP) gene family function as channels through which receptor-operated and store-operated Ca²⁺ entry (SOCE) occur. In the present study, the presence of TRPC1, TRPC3, TRPC4, TRPC5, and TRPC6 mRNA and protein expression was confirmed in cultured HASMCs using RT-PCR and Western blot analysis. TNF-α treatment significantly increased TRPC3 mRNA and protein levels in HASMCs as well as SOCE. TNF-α treatment also increased both the peak and plateau intracellular Ca²⁺ concentration responses in HASMCs elicited by acetylcholine and bradykinin. The effects of TNF-α treatment on SOCE and agonist-induced intracellular Ca²⁺ concentration responses were attenuated using small interfering RNA transfection, which knocked down TRPC3 expression. Thus, in inflammatory airway diseases, TNF-α treatment may result in increased myocyte activation due to altered Ca²⁺ influx pathways. These results suggest that TRPC3 may be an important therapeutic target in inflammatory airway diseases such as asthma and chronic obstructive pulmonary disease.