Mechanical properties of smooth muscle cells in the walls of arterial resistance vessels.

1. Methods have been developed for measuring the dynamic mechanical response of arterial resistance vessels (i.d. 83--235 micrometer) with a time resolution of about 4 msec. 2. Observations of the microscope image of the smooth muscle cells in the walls of these vessels indicate that there is little intercellular compliance in this preparation, and that the mechanical properties of the activated preparation are a reflexion of the mechanical properties of the individual smooth muscle cells. 3. Under isometric conditions the force developed per unit cell area was about 350 mN/mm2. Under isotonic conditions the cells had a maximum velocity for shortening at 37 degrees C of about 0.17 lengths/sec. 4. Quick releases of activated vessels indicate that the instantaneous elastic characteristic of smooth muscle cells is approximately exponential. 5. The wall tension response to small (0.3%) square wave changes in circumference was proportional to the logarithm of the time following the start of each circumference change. 6. Active wall tension, deltaT, was varied by varying the Ca2+ concentration of the activating solution. Under these conditions the active dynamic stiffness, k, was proportional to deltaT, and was not temperature dependent. The active half response time, tau (the time, taken to recover half the tension change caused by a small change in circumference) was also proportional to deltaT, but here the constant of proportionality had a Q10 of about 1.8. 7. It is concluded that the quick release response and the square wave response are in part a function of the mechanical properties of the crossbridges between the contractile filaments. Calculations show that both these responses can be explained if it is assumed that there is a relatively compliant passive component in series with the crossbridges.