Abstract
The primary function of the well-differentiated ciliated epithelium in the human paranasal sinuses is to eliminate microorganisms, debris, and foreign particles through the beating action of cilia. While factors regulating ciliary activity are not fully understood, we have demonstrated the expression of different nitric oxide synthase (NOS) isoforms in cultured human paranasal epithelial cells and have shown that ciliary activity in these cells is upregulated via an NO-dependent mechanisim. In this study, we studied the function of endogenously generated NO in signal transduction and discuss the role of NO synthesized by different isoforms with the ciliated cell. Cultured human paranasal sinus epithelium was incubated either with TNF-α (1ng/ml), dexamethazone (10-6M), or nothing for 24 hours. Ciliary beat frequency (CBF) of ciliated cells in each group was measured photoelectrically at baseline and after the addition of 1mM each of L-arginine, L-NAME (a non specific NOS inhibitor), or S-ethylisothiourea (EIT, a specific inducible NOS inhibitor). The addition of L-arginine rapidly increased CBF in the untreated group (18.7%) and in the dexamethazone-treated group (21.5%), whereas the increase in the TNF-α-treated group was 9.2%, significantly lower than in the other 2 groups. The addition of EIT significantly increased CBF in the TNF-α-treated group (12.1%), but neither of the other 2 groups showed a significant change in CBF from the baseline. L-NAME rapidly decreased CBF by 17-21% within 5 minutes in all groups, decreases that were not statistically significant between groups. Immunocytochemical studies demonstrated constitutive endothelial NOS (eNOS) expression in all groups and strong iNOS reactivity in cells treated with TNF-α, indicating that NO generation by epithelial ciliated cells is mediated via different NOS isoforms and is constitutively involved in CBF regulation. We further surmise that NO modulates CBF in cultured sinus ciliated cells differently under conditions when iNOS expression is strongly augmented inside the cells.
