Beyond the dogma:: novel β2-adrenoceptor signalling in the airways

beta(2)-Adrenoceptor agonists evoke rapid bronchodilatation and are the mainstay of the treatment of asthma symptoms worldwide. The mechanism of action of this class of compounds is believed to involve the stimulation of adenylyl cyclase and subsequent activation of the cyclic adenosine monosphosphate (cAMP)/cAMP-dependent protein kinase cascade. This classical model of beta(2)-adrenoceptor-mediated signal transduction is deeply entrenched, but there is compelling evidence that agonism of beta(2)-adrenoceptors can lead to the activation of multiple effector pathways, which now compels researchers in academia and the pharmaceutical industry alike to think beyond the traditional dogma. Therefore, the regulation by beta(2)-adrenoceptor agonists of responses, including airways smooth muscle tone and the secretory capacity of the epithelium and pro-inflammatory/immune cells, may be highly complex, involving both cAMP-dependent and -independent mechanisms that, in many cases, may act in concert. In this article, the current status of beta(2)-adrenoceptor-mediated signalling in the airways is reviewed in the context of understanding mechanisms that may underlie both the beneficial and detrimental effects of these drugs in asthma symptom management.