, 2011).

By acting on M3 coupled G-protein receptors (GPCR) Fulvestrant present in bronchial smooth muscle, MCh enhances the contraction of airway smooth muscle via Ca2+-dependent and Ca2+-independent pathways. The activation of phospholipase C and CD38 pathways enhances free cytosolic Ca2+, which promotes the calmodulin-dependent activation of myosin light chain kinase (MLCK). In addition, activated Rho kinases inhibit myosin light chain phosphatase (MLCP), enhancing iCa2+ sensitivity. Both intracellular pathways induce the coupling of myosin light chain (MLC) and cell contraction ( Amrani and Panettieri, 1998 and Murthy, 2006). Our data show that in vivo HQ exposure favours these pathways, leading to enhanced tracheal contraction in response to MCh. Moreover,

we clearly show that this is not a direct effect of HQ, but is dependent on HQ-induced TNF secretion by epithelial cells. This evidence was obtained by removing epithelial cells from tracheas, after which the MCh-induced tracheal reactivity of HQ-exposed animals was equivalent to that observed in trachea obtained from control animals. The literature suggests that an increase in airway responsiveness is closely associated with acute airway inflammation, depending on the presence of inflammatory cells, not only eosinophils, but also neutrophils in the airway system (Cockcroft and Davis, 2006 and Nakagome and Nagata, 2011). Controversially, our findings show that this may not be the mechanism underlying HQ-induced upper airway hyperresponsiveness, as neutrophil infiltration and/or Trichostatin A morphological Casein kinase 1 changes were not found in the tracheal tissue after HQ exposure. Corroborating this data, our group has recently demonstrated that HQ exposure per se did not induce the migration of inflammatory cells into the lung tissue. On the contrary, it impairs the LPS-induced infiltration of polymorphonuclear and mononuclear cells into the lungs ( Ribeiro et al., 2011 and Shimada

et al., in press). It has been proposed that HQ in vitro causes smooth muscle cell contraction in the guinea-pig trachea, rabbit aorta and rat/mouse anococcygeus muscle ( Güc et al., 1988, Hobbs et al., 1991 and Ilhan and Sahin, 1986) by acting as a NO scavenger ( Hobbs et al., 1991). The participation of NO was ruled out in the present study, since HQ exposure did not modify the secretion of NO2− by tracheal tissue. In fact, as mentioned earlier, our findings demonstrate that HQ-induced tracheal hyperresponsiveness was strongly related to TNF secretion by tracheal epithelial cells. The role of TNF in cholinergic-induced smooth muscle cell contraction, as observed in this study, has been demonstrated previously (Adner et al., 2002, Thomas, 2001 and Thomas et al., 1995), but the mechanisms of actions remain unclear.