The temperature dependence of parallel and series elastic elements in the vascular smooth muscle of the rat portal vein.

The stiffness of a parallel (PE) as well as of a series elastic element (SE) in the isolated rat portal vein was determined at 37 degrees C and at 25 degrees C. The length-tension curve of the PE was obtained by a stepwise lengthening of the preparation and showed no temperature dependence for the element: the mean extension of the PE was 48.8% of the optimum length L0 at 37 degrees C, and 47.3% of L0 at 25 degrees C when loaded with the maximum active force T0. The maximum force occurred at both temperatures with the same muscle length. Even the stiffness factor, i.e. the slope 'k' of the linear function dT/dL = k . T + c showed no temperature dependence. The series elasticity was determined by means of the quick-release technique from afterloaded isometric contractions of the tetanized preparation. A distinct temperature influence was revealed by the decrease of the mean SE extension from 13.5% of L0 at 37 degrees C to 10.9% of L0 at 25 degrees C (P less than 0.0005). The stiffness factor, normalized to the actual muscle length, was 12.0 per ML at 37 degrees C and 14.7 per ML at 25 degrees C (P less than 0.025). The values obtained for the portal vein are equivalent to those calculated for other smooth muscle preparations but the stiffness of series elasticity is well below that found in the cardiac and skeletal muscle.