Original Article Regional differences of energetics, mechanics, and kinetics of myosin cross-bridge in human ureter smooth muscle

This study provides information about baseline mechanical properties of the entire muscle and the mo- lecular contractile mechanism in human ureter smooth muscle and proposed to investigate if changes in mechani- cal motor performance in different regions of isolated human ureter are attributable to differences in myosin cross- bridge interactions. Classic mechanical, contraction 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 cross- bridge number per mm 2 (Ψ), elementary force per single crossbridge (Π 0 ), duration of maximum rate constant of crossbridge attachment 1/f 1 and detachment 1/g 2 and peak mechanical efficiency (Eff. max ). Abdominal longitudi- nal smooth muscle strips exhibited significantly higher maximum isometric tension and faster maximum unloaded shortening velocity compared to pelvic ones. Contractile differences were associated with significantly higher cross - bridge number per mm 2 . 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 showed better mechanical motor performance mainly related to a higher crossbridge number and crossbridge kinetics differences. Such results were more evident in the longitudinal rather than in the circular layer.