Abstract
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. Peak T-a at the new length was not different from the original peak T-a, and the L-T-p curve shifted rightward with the L-T-a curve. Multiple contractions on the ascending limb increased both T-a and T-p. In contrast, multiple contractions on the descending limb increased T-a but decreased T-p. The T-p/T-a ratio on the original descending limb adapted from 0.540 +/- 0.084 to 0.223 +/- 0.033 (mean +/- SE, n = 7), such that it was not different from the ratio of 0.208 +/- 0.033 at the original peak T-a length, suggesting a role of length adaptation may be to maintain a desirable T-p/T-a ratio as the bladder fills and voids over a broad DSM length range.