Slowly cycling Rho kinase-dependent actomyosin cross-bridge “slippage” explains intrinsic high compliance of detrusor smooth muscle

Abstract

Biological soft tissues are viscoelastic because they display time-independent pseudoelasticity and time-dependent viscosity. However, there is evidence that the bladder may also display plasticity, defined as an increase in strain that is unrecoverable unless work is done by the muscle. In the present study, an electronic lever was used to induce controlled changes in stress and strain to determine whether rabbit detrusor smooth muscle (rDSM) is best described as viscoelastic or viscoelastic plastic. Using sequential ramp loading and unloading cycles, stress-strain and stiffness-stress analyses revealed that rDSM displayed reversible viscoelasticity, and that the viscous component was responsible for establishing a high stiffness at low stresses that increased only modestly with increasing stress compared with the large increase produced when the viscosity was absent and only pseudoelasticity governed tissue behavior. The study also revealed that rDSM underwent softening correlating with plastic deformation and creep that was reversed slowly when tissues were incubated in a Ca-containing solution. Together, the data support a model of DSM as a viscoelastic-plastic material, with the plasticity resulting from motor protein activation. This model explains the mechanism of intrinsic bladder compliance as "slipping" cross bridges, predicts that wall tension is dependent not only on vesicle pressure and radius but also on actomyosin cross-bridge activity, and identifies a novel molecular target for compliance regulation, both physiologically and therapeutically.

A new bladder‐emptying method in females with neurogenic bladder: A randomized, phase II trial

“…These results are in agreement with data from the previous reports that showed bladder capacity gain due to the reduction of urinary loss . Experimental studies have also presented an improvement of bladder compliance after detrusor musculature distension …”

“…17,18 Experimental studies have also presented an improvement of bladder compliance after detrusor musculature distension. 12,19,20 The proportion of total adverse events in the ISRD group was approximately half of those found in the CIC group, while more than 50% of the patients in the ISRD group did not present any side effects. This result is in agreement with the data obtained in the pilot study 11 and with previous studies that idealized alternative devices to CIC.…”

What are the origins and relevance of spontaneous bladder contractions? ICI‐RS 2017

“…A normal bladder can accommodate a broad range of volumes at relatively low filling pressures while simultaneously providing sufficient wall tension to maintain an efficient shape in the presence of abdominal loads (ie, a low bladder wall surface area to volume ratio). To accomplish these functions the bladder exhibits viscoelastic, reversibly plastic behavior, 48,49 and acutely adjustable preload tension. 50,51 Bladder contractions, including spontaneous rhythmic contractions, can modify preload by adjusting resting muscle strain.…”

“…50,51 Bladder contractions, including spontaneous rhythmic contractions, can modify preload by adjusting resting muscle strain. 49,52 Adjustable preload is due to cross-bridges and slippage of these cross-bridges during the relaxation phase of a spontaneous contraction that may allow accommodation during filling. 49 Adjustable preload has been quantified as dynamic elasticity during urodynamics 53 ; however, the effect of spontaneous contractions on this behavior has yet to be studied clinically.…”

“…To accomplish these functions the bladder exhibits viscoelastic, reversibly plastic behavior, 48,49 and acutely adjustable preload tension. 50,51 Bladder contractions, including spontaneous rhythmic contractions, can modify preload by adjusting resting muscle strain.…”