title: [Origin of motion in the human ureter: mechanics, energetics and kinetics of the myosin molecular motors].
abstract: BACKGROUND
  Ureteral peristalsis is the result of coordinated mechanical motor performance of longitudinal and circular smooth muscle layer of the ureter wall. The main aim of this study was to characterize in smooth muscle of proximal segments of human ureter, the mechanical properties at level of muscle tissue and at level of myosin molecular motors.
  
  
  METHODS
  Ureteral samples were collected from 15 patients, who underwent nephrectomy for renal cancer. Smooth muscle strips longitudinally and circularly oriented from proximal segments of human ureter were used for the in vitro experiments. Mechanical indices including the maximum unloaded shortening velocity (Vmax), and the maximum isometric tension (P0) normalized per cross-sectional area, were determined in vitro determined in electrically evoked contractions of longitudinal and circular smooth muscle strips. Myosin cross-bridge (CB) number per mm2 (Ψ) the elementary force per single CB (Ψ) and kinetic parameters were calculated in muscle strips, using Huxley's equations adapted to nonsarcomeric muscles.
  
  
  RESULTS
  Longitudinal smooth muscle strips exhibited a significantly (p<0.05) faster Vmax (63%) and a higher P0 (40%), if compared to circular strips. Moreover, longitudinal muscle strips showed a significantly higher unitary force (Ψ) per CB. However, no significant differences were observed in CB number, the attachment (f1) and the detachment (g2) rate constants between longitudinal and circular muscle strips.
  
  
  CONCLUSIONS
  The main result obtained in the present work documents that the mechanical, energetic and unitary forces per CB of longitudinal layer of proximal ureter are better compared to the circular one; these preliminary findings suggested, unlike intestinal smooth muscle, a major role of longitudinal smooth muscle layer in the ureter peristalsis.
authors.affiliation: Dip. di Scienze della Vita e dell'Ambiente, Università di Cagliari, Cagliari, Italy. rvargiu@unica.it
authors.forename: Romina
authors.initials: R
authors.lastname: Vargiu
authors.forename: Anna
authors.initials: A
authors.lastname: Perinu
authors.forename: Antonello
authors.initials: A
authors.lastname: De Lisa
authors.forename: Frank
authors.initials: F
authors.lastname: Tintrup
authors.forename: Francesco
authors.initials: F
authors.lastname: Manca
authors.forename: Rino
authors.initials: R
authors.lastname: Mancinelli
mesh_terms: D000205:Actomyosin / Q000502:physiology*; D000328:Adult; D001696:Biomechanical Phenomena; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007537:Isometric Contraction; D008297:Male; D008875:Middle Aged; D009130:Muscle, Smooth / Q000502:physiology; D009218:Myosins / Q000502:physiology*; D010528:Peristalsis / Q000502:physiology*; D014513:Ureter / Q000502:physiology*
chemical_list: D000205:Actomyosin; D009218:Myosins