However, since phenanthrolin induced relaxation was less affected and since dapsone or flufenamic acid induced re laxation were not affected at all, non TAS2R mediated mechanisms such as effect on potassium, sodium sellectchem or cal cium ion channels or membrane stabilizing Inhibitors,Modulators,Libraries properties may explain the results with chloroquine. These re sults nevertheless suggest that the described modulation of L type voltage gated calcium channels is not sufficient to fully explain the TAS2R induced bronchial relaxation. The cAMP pathway is obviously a major intracellular signalling pathway in the regulation of bronchial smooth muscle tone. It has been reported that some TAS2R sub types impair the activity of phosphodiesterases via the gustducin subunit. Furthermore, TAS2R receptors may be coupled directly to adenylate cyclase.
The results of our experiments with pharmacological inhibitors of the cAMP downstream signalling proteins PKA and Epac suggest that these cAMP dependent pathways are not involved in the TAS2R agonist related relaxation, which is in agreement with the absence of Inhibitors,Modulators,Libraries any increase in the cAMP concentra tion following the treatment of guinea pig tracheas with TAS2R agonists. Furthermore, endogenous broncho dilators of epithelial origin are unlikely to be involved in TAS2R agonist related relax ation, due to the non significant effect of nitric oxide syn thase and cyclooxygenase inhibitors. In guinea pig trachea, chloroquine induced relaxation was also not affected by indomethacin. In our experiments, epithelium re moval affected phenanthroline induced relaxation but not chloroquine induced relaxation.
The Inhibitors,Modulators,Libraries relaxation in response to phenanthroline is therefore dependent on an intact epithelium. Phenanthroline is an exclusive TAS2R5 agonist, whereas chloroquine activates a wider range of receptors. hence, receptor expression dif ferences between epithelial cells and smooth Inhibitors,Modulators,Libraries muscle cells may explain this result. We lastly focused on the role of phosphoinositide 3 kinases. The inhibitors of PI3K wortmannin and PI 828 potentiated the relaxation to chloroquine and phenanthro line but did not affect the relaxation to isoproterenol. Wortmannin is described be a non selective PI3K inhibitor since it also inhibits polo like kinase family with an IC50 in the same range as for PI3K, or other enzymes such as mTOR, myosin light chain kinase and mitogen activated protein kinase .
whereas PI 828 selectively targets PI3K. Our data suggest an increase in sensitivity of human bronchi to bitter agonists after incubation with the PI3K inhibitors whereas PI3K do not seem to be involved in the response Inhibitors,Modulators,Libraries to B2 adrenoreceptor agonists. However, our attempts to induce a right shift in the concentration response curves to bitter agonists selleckchem with the selective PI3K activator 740 Y P were unsuccessful.