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

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Abstract
Methods were developed for measuring the dynamic mechanical response of [rat intestinal mesentery] arterial resistance vessels (i.d. 83-235 .mu.m) with a time resolution of about 4 ms. Observations of the microscope image of the smooth muscle cells in the walls of these vessels indicate there is little intercellular compliance in this preparation, and the mechanical properties of the activated preparation are a reflection of the mechanical properties of the individual smooth muscle cells. Under isometric conditions the force developed/unit cell area was about 350 mN/mm2. Under isotonic conditions the cells had a maximum velocity for shortening at 37.degree. C of about 0.17 lengths/s. Quick releases of activated vessels indicate that the instantaneous elastic characteristic of smooth muscle cells is approximately exponential. 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. Active wall tension, .DELTA.T, was varied by varying the Ca2+ concentration of the activating solution. Under these conditions the active dynamic stiffness, k, was proportional to .DELTA.T, 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 .DELTA.T, but here the constant of proportionality had a Q10 of about 1.8. 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 these responses can be explained if it is assumed there is a relatively compliant passive component in series with the crossbridges.