Aim: 

Ureteral peristalsis is the result of coordinated mechanical motor performance of longitudinal (Lsm) and circular (Csm) smooth muscle layers. Only limited information is available on the intrinsic contractile properties of ureteral smooth muscle during peristalsis. The aim of the present study was therefore to assess in both Lsm and Csm the baseline mechanical properties at the level of both the entire muscle and molecular motors.

Methods: 

Maximum shortening velocity (V_max), the maximum normalised isometric tension (P0) and the maximum power developed (P_out-put) were in vitro determined in Lsm and Csm of human ureter. Using A.F. Huxley' equations adapted to smooth muscle we calculated the total cycling of cross-bridges (CB) per mm² (Yx10⁹), the elementary force per single CB (P), the maximum value of the rate constant for GB attachment (f1) and detachment (g2).

Results: 

Lsm exhibited a significant increase (p<0.05) in P0 (40%), in V_max (63%) and in Pout-put (83%) as compared to Csm. Differences in mechanical performance were associated with a significant increase in P (0,80 ± 0,12 pN in Lsm vs. 0,64 ± 0,16 pN in Lsm) without significant changes in (Yx10⁹ ) (11,34 ± 5,2 x mm^-2 in Lsm vs. 9,19 ± 5,06 x mm^-2 in Csm). No significant differences were found in f1 and g2 kinetic parameters between Lsm and Csm.

Conclusion: 

These results document that in the human ureter smooth muscle myosin molecular motor developed a greater unitary force in Lsm than in Csm indicating that, unlike in the intestine, in the human ureteral wall longitudinal smooth muscle layer appears to play a major role in the propulsion of intraluminal content.