Does smooth muscle in an intact airway undergo length adaptation during a sustained change in transmural pressure?
In isolated airway smooth muscle (ASM) strips, an increase or decrease in ASM length away from its current optimum length causes an immediate reduction in force production followed by a gradual time-dependent recovery in force, a phenomenon termed length adaptation. In situ, length adaptation may be initiated by a change in transmural pressure (Ptm), which is a primary physiological determinant of ASM length. The present study sought to determine the effect of sustained changes in Ptm and therefore, ASM perimeter, on airway function. We measured contractile responses in whole porcine bronchial segments in vitro before and after a sustained inflation from a baseline Ptm of 5 cmH2O to 25 cmH2O, or deflation to -5 cmH2O, for ∼50 min in each case. In one group of airways, lumen narrowing and stiffening in response to electrical field stimulation (EFS) were assessed from volume and pressure signals using a servo-controlled syringe pump with pressure feedback. In a second group of airways, lumen narrowing and the perimeter of the ASM in situ were determined by anatomical optical coherence tomography. In a third group of airways, active tension was determined under isovolumic conditions. Both inflation and deflation reduced the contractile response to EFS. Sustained Ptm change resulted in a further decrease in contractile response, which returned to baseline levels upon return to the baseline Ptm. These findings reaffirm the importance of Ptm in regulating airway narrowing. However, they do not support a role for ASM length adaptation in situ under physiological levels of ASM lengthening and shortening.
School of Anatomy, Physiology and Human Biology, University of Western Australia, Crawley, Western Australia, Australia; School of Veterinary and Life Sciences, Murdoch University, Murdoch, Western Australia, Australia; t.ansell@murdoch.edu.au.
Thomas K
TK
Ansell
School of Anatomy, Physiology and Human Biology, University of Western Australia, Crawley, Western Australia, Australia;
Peter K
PK
McFawn
Optical+Biomedical Engineering Laboratory, School of Electrical, Electronic and Computer Engineering, University of Western Australia, Crawley, Western Australia, Australia;
Robert A
RA
McLaughlin
Optical+Biomedical Engineering Laboratory, School of Electrical, Electronic and Computer Engineering, University of Western Australia, Crawley, Western Australia, Australia; Centre for Microscopy, Characterisation and Analysis, University of Western Australia, Crawley, Western Australia, Australia;
David D
DD
Sampson
School of Anatomy, Physiology and Human Biology, University of Western Australia, Crawley, Western Australia, Australia; West Australian Sleep Disorders Research Institute, Sir Charles Gairdner Hospital, Nedlands, Western Australia, Australia; and.
Peter R
PR
Eastwood
West Australian Sleep Disorders Research Institute, Sir Charles Gairdner Hospital, Nedlands, Western Australia, Australia; and.
David R
DR
Hillman
School of Anatomy, Physiology and Human Biology, University of Western Australia, Crawley, Western Australia, Australia;
Howard W
HW
Mitchell
School of Anatomy, Physiology and Human Biology, University of Western Australia, Crawley, Western Australia, Australia; Centre for Neonatal Research and Education, School of Paediatrics and Child Health, University of Western Australia, Crawley, Western Australia, Australia.
Peter B
PB
Noble
D000222:Adaptation, Physiological / Q000502:physiology*; D000818:Animals; D001980:Bronchi / Q000502:physiology / Q000503:physiopathology; D016084:Bronchoconstriction / Q000502:physiology; D004558:Electric Stimulation / Q000379:methods; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D009130:Muscle, Smooth / Q000502:physiology*; D011312:Pressure; D012137:Respiratory System / Q000503:physiopathology*; D013552:Swine
airway smooth muscle; anatomical optical coherence tomography (aOCT); bronchoconstriction; length adaptation