Carbachol-induced volume adaptation in mouse bladder and length adaptation via rhythmic contraction in rabbit detrusor.

The length-tension (L-T) relationships in rabbit detrusor smooth muscle (DSM) are similar to those in vascular and airway smooth muscles and exhibit short-term length adaptation characterized by L-T curves that shift along the length axis as a function of activation and strain history. In contrast to skeletal muscle, the length-active tension (L-T(a)) curve for rabbit DSM strips does not have a unique peak tension value with a single ascending and descending limb. Instead, DSM can exhibit multiple ascending and descending limbs, and repeated KCl-induced contractions at a particular muscle length on an ascending or descending limb display increasingly greater tension.

Length adaptation of the passive-to-active tension ratio in rabbit detrusor.

The passive and active length-tension (L-T (p) and L-T (a)) relationships in airway, vascular, and detrusor smooth muscles can adapt with length changes and/or multiple contractions. The present objectives were to (1) determine whether short-term adaptation at one muscle length shifts the entire L-T (a) curve in detrusor smooth muscle (DSM), (2) compare adaptation at shorter versus longer lengths, and (3) determine the effect of adaptation on the T (p)/T (a) ratio. Results showed that multiple KCl-induced contractions on the descending limb of the original L-T (a) curve adapted DSM strips to that length and shifted the L-T (a) curve rightward.

Rhythmic contraction generates adjustable passive stiffness in rabbit detrusor.

The length-tension (L-T) relationships in airway and vascular smooth muscles have been shown to adapt with length changes over time. Our prior studies have shown that the active and passive L-T relationships in rabbit detrusor smooth muscle (DSM) can adapt and that DSM exhibits adjustable passive stiffness (APS) characterized by a passive L-T curve that is a function of strain and activation history. The present study demonstrates that passive tension due to APS can represent a substantial fraction of total tension over a broad length range.

Adaptation of the length-active tension relationship in rabbit detrusor.

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.