Mechanical properties of smooth muscle. I. Length-tension and force-velocity relations.

GORDON, ALLEN R., AND MARION J. SIEGMAN. Mechanical properties of smooth muscle. I. Length-tension and force-velocity relations. Am. J. Physiol. 221 (5) : 1243-1249. 1971 .-The length-tension and force-velocity relationships of rabbit taenia coli were studied at 22 C. The absence of spontaneous mechanical activity at this temperature was confirmed by test applications of epinephrine. The muscles were tetanically stimulated by means of a maximal 60 Hz, a-c transverse field. An optimum length for tension development was exhibited at which the passive tension was 30yo of the total tension. The maximum developed tension at the optimum length was 0.89 h 0.11 kg/cm2. The inverse relationship between the load or developed tension and the maximum velocity of shortening could be described by the Hill equation. The dynamic constants from the Hill equation were independent of the initial muscle length (a/P,1 = 0.331 zt 0.051; b/l = 0.010 =~t O.OOl/sec.; and V,,,/Z = 0.03 1 &. 0003/set). The similarity of these mechanical properties and those of skeletal muscle suggests that a similar mechanism of contraction exists in taenia coli.