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Adaptive response of pulmonary arterial smooth muscle to length change

¹Department of Anesthesiology, Pharmacology, and Therapeutics, ²The James Hogg iCAPTURE Centre, and ³Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, British Columbia, Canada

Submitted 11 November 2007 ; accepted in final form 19 January 2008

Hypervasoconstriction 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 (12–16 s, 20 V, 60 Hz). The length-force relationship was determined at L_ref to 0.6 L_ref, where L_ref was a reference length close to the in situ length of PASM. The response to length oscillations was determined at L_ref, after the muscle was subjected to length oscillation of various amplitudes for 200 s at 1.5 Hz. Release (or stretch) of resting PASM from L_ref 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 monoexponential time course. Length oscillations with amplitudes ranging from 5 to 20% L_ref 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 hypervasoconstriction in pulmonary hypertension.

blood vessel; mechanics; length-force relationship