Involvement of Ca(2+) Signaling in the Synergistic Effects between Muscarinic Receptor Antagonists and β(2)-Adrenoceptor Agonists in Airway Smooth Muscle

Long-acting muscarinic antagonists (LAMAs) and short-acting β(2)-adrenoceptor agonists (SABAs) play important roles in remedy for COPD. To propel a translational research for development of bronchodilator therapy, synergistic effects between SABAs with LAMAs were examined focused on Ca(2+) signaling using simultaneous records of isometric tension and F340/F380 in fura-2-loaded tracheal smooth muscle. Glycopyrronium (3 nM), a LAMA, modestly reduced methacholine (1 μM)-induced contraction. When procaterol, salbutamol and SABAs were applied in the presence of glycopyrronium, relaxant effects of these SABAs are markedly enhanced, and percent inhibition of tension was much greater than the sum of those for each agent and those expected from the BI theory. In contrast, percent inhibition of F340/F380 was not greater than those values. Bisindolylmaleimide, an inhibitor of protein kinase C (PKC), significantly increased the relaxant effect of LAMA without reducing F340/F380. Iberiotoxin, an inhibitor of large-conductance Ca(2+)-activated K(+) (K(Ca)) channels, significantly suppressed the effects of these combined agents with reducing F340/F380. In conclusion, combination of SABAs with LAMAs synergistically enhances inhibition of muscarinic contraction via decreasing both Ca(2+) sensitization mediated by PKC and Ca(2+) dynamics mediated by K(Ca) channels. PKC and K(Ca) channels may be molecular targets for cross talk between β(2)-adrenoceptors and muscarinic receptors.