Rate-limiting steps in the tension development of freeze-glycerinated vascular smooth muscle

A method for "skinning" arterial smooth muscle is presented which yields isometric tension development typically 60-80% of maximum physiological tension in the presence of micromolar Ca++ and millimolar Mg-ATP, while retaining essentially the native protein content. Using the methods of "CA jump," the time-course of Ca++-activated tension development in the skinned artery can be made identical to, but not faster than, the rate of tension development in the intact artery. In the skinned artery, activating free [Ca++] does not substantially alter the rate at which tension development approaches the final steady tension attained at that free [Ca++] (less than 25% decline in speed for a 10-fold decrease in [Ca++]). These observations are taken to mean that the rate-limiting step in isometric tension development in arterial smooth muscle does not depend directly on Ca++.