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J Appl Physiol 103: 1462, 2007; doi:10.1152/japplphysiol.00629.2007
8750-7587/07 $8.00
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LETTER TO THE EDITOR

Commentary on "The role of the large airways on smooth muscle contraction in asthma"

TO THE EDITOR: Permutt's Viewpoint (3) stating that "narrowing of large airways causes dynamic hyperinflation," which, in turn, is a major determinant of airway hyperresponsiveness, is very important. Equally important is his finding that there was no evidence that small airways played a significant role in the increase in residual volume (RV) produced by baseline smooth muscle tension (BSMT; Ref. 1). Some of our work provides support for these points of view (2). We measured maximum velocity (Vo) and capacity ({Delta}Lmax) of shortening of the electrically stimulated, zero-loaded airway smooth muscle. This Vo may be used as an index of actin-activated Ca2+-Mg2+-ATPase activity. Airway generations studied ranged from the trachea to the sixth lobar bronchus. We found (2) muscle contractility progressively decreased down the airway tree, as gauged by the behavior of Vo and maximum shortening capacity ({Delta}Lmax). We also found by cluster analysis that airway contractility could be divided into two groups; one an extrapulmonary group consisting of trachealis and bronchial generations 1 and 2 and, the other, an intrapulmonary group that extended from the third to the sixth generation. The first group possessed a faster Vo and greater {Delta}Lmax than the second.

Our findings could provide the isolated muscle underpinnings for Permutt's Viewpoint.

FOOTNOTES


Address for correspondence: N. Stephens, 715 McDermot Ave, Room 537 John Buhler Research Centre, Winnipeg Manitoba, Canada R3E 3P4 (e-mail: nstephe{at}ms.umanitoba.ca)

REFERENCES

  1. Brown RH, Pearse DB, Pyrgos G, Liu MC, Togias A, Permutt S. The structural basis of airways hyperresponsiveness in asthma. J Appl Physiol 101: 30–39, 2006.[Abstract/Free Full Text]
  2. Ma X, Li W, Stephens NL. Detection of two clusters of mechanical properties of smooth muscle along the airway tree. J Appl Physiol 80: 857–861, 1996.[Abstract/Free Full Text]
  3. Permutt S. Viewpoint: The role of the large airways on smooth muscle contraction in asthma. J Appl Physiol; 10.1152/japplphysiol.00568.2007.

Newman Stephens
 Department of Physiology, University of Manitoba, Winninpeg Manitoba, Canada





This Article
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