Submitted on November 11, 2007
Accepted on January 19, 2008
Adaptive Response of Pulmonary Arterial Smooth Muscle to Length Change
Harley Syyong1, Christine Cheung2, Dennis Solomon3, Chun Y. Seow3*, and Kuo H. Kuo4
1 Department of Anesthesiology, Pharmacology, and Therapeutics, University of British Columbia, Vancouver, Canada
2 The James Hogg iCAPTURE Centre, University of British Columbia, Vancouver, Canada
3 Vancouver, Canada; The James Hogg iCAPTURE Centre, University of British Columbia, Vancouver, Canada
4 Vancouver, Canada; Department of Anesthesiology, Pharmacology, and Therapeutics, University of British Columbia, Vancouver, Canada
* To whom correspondence should be addressed. E-mail: cseow{at}mrl.ubc.ca.
Hyper-vasoconstriction is associated with pulmonary hypertension and dysfunction of the pulmonary arterial smooth muscle (PASM) is implicated. However, relatively little is known about the mechanical properties of PASM. Recent advances in our understanding of plastic adaptation in smooth muscle may shed light on the disease mechanism. In this study we determined whether PASM is capable of adapting to length changes (especially shortening) and regain its contractile force. We examined the time course of length adaptation in PASM in response to step-changes in length and to length oscillations mimicking the periodic stretches due to pulsatile arterial pressure. Rings from sheep pulmonary artery were mounted on myograph and stimulated using electrical field stimulation (12-16s, 20V, 60Hz). The length-force relationship was determined at Lref to 0.6 Lref, where Lref was a reference length close to the in situ length of PASM. The response to length oscillations was determined at Lref, after the muscle was subjected to length oscillation of various amplitudes for 200s at 1.5Hz. Release (or stretch) of resting PASM from Lref to 0.6 (and vice versa) was followed by a significant force recovery (73% and 63% respectively), characteristic of length adaptation. All recoveries of force followed a mono-exponential time course. Length oscillations with amplitudes ranging from 5 to 20% Lref caused no significant change in force generation in subsequent contractions. It is concluded that, like many smooth muscles, PASM possesses substantial capability to adapt to changes in length. Under pathological conditions, this could contribute to hyper-vasoconstriction in pulmonary hypertension.
