Airway Smooth Muscle in BHR 73 Clinical Reviews in Allergy & Immunology Volume 24, 2003 73 *Author to whom all correspondence and reprint requests should be addressed. E-mail: jsolway@ medicine.bsd.uchicago.edu Clinical Reviews in Allergy and Immunology © Copyright 2003 by Humana Press Inc. 1080-0549/03/73–84/$20.00 Index Entries: Abstract Bronchial hyperresponsiveness (BHR), the occurrence of excessive bronchoconstriction in response to relatively small constrictor stimuli, is a cardinal feature of asthma. Here, we con- sider the role that airway smooth muscle might play in the generation of BHR. The weight of evidence suggests that smooth muscle isolated from asthmatic tissues exhibits normal sensi- tivity to constrictor agonists when studied during isometric contraction, but the increased muscle mass within asthmatic airways might generate more total force than the lesser amount of muscle found in normal bronchi. Another salient difference between asthmatic and normal individuals lies in the effect of deep inhalation (DI) on bronchoconstriction. DI often substan- tially reverses induced bronchoconstriction in normals, while it often has much less effect on spontaneous or induced bronchoconstriction in asthmatics. It has been proposed that abnor- mal dynamic aspects of airway smooth muscle contraction—velocity of contraction or plastic- ity-elasticity balance—might underlie the abnormal DI response in asthma. We suggest a speculative model in which abnormally long actin filaments might account for abnormally increased elasticity of contracted airway smooth muscle. Asthma; deep breath; inhalation; actin; hyperresponsive. What Evidence Implicates Airway Smooth Muscle in the Cause of BHR? Nickolai O. Dulin 1 , Darren J. Fernandes 1 , Maria Dowell 1 , Shashi Bellam 1 , John McConville 1 , Oren Lakser 2 , Richard Mitchell 1 , Blanca Camoretti-Mercado 1 , Paul Kogut 1 , and Julian Solway *,1 1 Section of Pulmonary and Critical Care Medicine, Department of Medicine, University of Chicago, Chicago, IL; and 2 Department of Pediatrics, Children’s Memorial Hospital and Northwestern University, Chicago, IL