Nuove osservazioni sulla biomeccanica dell’uretere umano

The function of ureter is to transport the urine from the kidney to the urinary bladder. Ureteral peristalsis, the principal motor event that propels urine along the ureter, is the result of coordinated contractions of longitudinal and circular smooth muscle inside the organ wall. Alterations of static and dynamic biomechanical properties of the ureteral wall lead to pathological states compromising regular urine transportation to bladder. Although knowledge on ureteral motility has advanced considerably, the molecular contractile mechanism of ureteral smooth muscle cells is not fully understood. This study provides information about baseline mechanical properties of the entire muscle and the molecular contractile mechanism in human ureter smooth muscle and proposed to investigate if changes in mechanical motor performance in different regions of isolated human ureter are attributable to differences in myosin crossbridge interactions. Classic mechanical, kinetic and energetic parameters derived from the tension-velocity relationship were studied in ureteral smooth muscle strips oriented longitudinally and circularly from abdominal and pelvic human ureter parts. By applying of Huxley’s mathematical model we calculated the total working crossbridge number per mm2 (Ψ), elementary force per single crossbridge (Π0), duration of maximum rate constant of crossbridge attachment 1/f1 and detachment 1/g2 and peak mechanical efficiency (Eff.max). Although no substantial differences exist in structural, biochemical and histological characteristics along the human ureter, abdominal longitudinal smooth muscle strips showed a higher maximum isometric tension, greater shortening, faster shortening velocity and higher maximum peak of work and power output than pelvic ones. Contractile differences were associated with significantly higher crossbridge number per mm2. Abdominal longitudinal muscle strips showed a lower duration of maximum rate constant of crossbridge attachment and detachment and higher peak mechanical efficiency than pelvic ones. Such data suggest that the abdominal human ureter exhibited better mechanical motor performance than pelvic ureter, mainly related to a higher crossbridge number and crossbridge kinetics differences. We believe that our results will be useful to understand better the physiology and physiopathology of ureteral smooth muscle, as well as improving the evaluation of pharmacological and surgical therapies in particular clinical cases.