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This Article Full Text Full Text (PDF) All Versions of this Article: 297/4/F1119    most recent 00298.2009v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Speich, J. E. Articles by Ratz, P. H. PubMed PubMed Citation Articles by Speich, J. E. Articles by Ratz, P. H.

Adaptation of the length-active tension relationship in rabbit detrusor

Departments of ¹Mechanical Engineering, ; ²Biomedical Engineering, ; ⁴Biochemistry and Molecular Biology and Pediatrics, and ; ³Division of Urology, Department of Surgery, Virginia Commonwealth University, Richmond, Virginia

Submitted May 22, 2009 ; accepted in final form August 10, 2009

Studies have shown that the length-tension (L-T) relationships in airway and vascular smooth muscles are dynamic and can adapt to length changes over a period of time. Our prior studies have shown that the passive L-T relationship in rabbit detrusor smooth muscle (DSM) is also dynamic and that DSM exhibits adjustable passive stiffness (APS) characterized by a passive L-T curve that can shift along the length axis as a function of strain history and activation history. The present study demonstrates that the active L-T curve for DSM is also dynamic and that the peak active tension produced at a particular muscle length is a function of both strain and activation history. More specifically, this study reveals that the active L-T relationship, or curve, does not have a unique peak tension value with a single ascending and descending limb, but instead reveals that multiple ascending and descending limbs can be exhibited in the same DSM strip. This study also demonstrates that for DSM strips not stretched far enough to reveal a descending limb, the peak active tension produced by a maximal KCl-induced contraction at a short, passively slack muscle length of 3 mm was reduced by 58.6 ± 4.1% (n = 15) following stretches to and contractions at threefold the original muscle length, 9 mm. Moreover, five subsequent contractions at the short muscle length displayed increasingly greater tension; active tension produced by the sixth contraction was 91.5 ± 9.1% of that produced by the prestretch contraction at that length. Together, these findings indicate for the first time that DSM exhibits length adaptation, similar to vascular and airway smooth muscles. In addition, our findings demonstrate that preconditioning, APS and adaptation of the active L-T curve can each impact the maximum total tension observed at a particular DSM length.

bladder; lower urinary tract; smooth muscle mechanics; length adaptation; preconditioning; strain softening; adjustable passive stiffness; passive force; active force