Mechanisms of Disease Airway receptors

Airway smooth muscle tone is influenced by many hormones, neurotransmitters, drugs and mediators, which produce their effects by binding to specific surface receptors on airway smooth muscle cells. Bronchoconstriction and bronchodilatation may therefore be viewed in terms of receptor activation or blockade and the contractile state of airway smooth muscle is probably the resultant effect of interacting excitatory and inhibitory receptors. It is important to recognize that airway calibre is not only the result of airway smooth muscle tone, but in asthma it is likely that airway narrowing may also be explained by oedema of the bronchial wall (resulting from microvascular leakage) and to luminal plugging by viscous mucus secretions and extravasated plasma proteins, which may be produced by a 'soup' of mediators released from inflammatory cells, including mast cells, macrophages and eosinophils. Activation of receptors on other target cells, such as submucosal glands, airway epithelium, post capillary venules, mast cells and other inflammatory cells may, therefore, also influence airway calibre. In this article I will concentrate on some of the receptors present on airway smooth muscle which may be relevant to airway disease.