Arterial smooth muscle Determinants of mechanical performance

The mechanical performance of arterial smooth muscle can be represented in terms of two measures: force development at constant muscle length and shortening at constant transmural pressure. In general, changes in the contractility of arterial smooth muscle are manifest as parallel changes in both measures of performance. In some instances, however, an apparent uncoupling exists in these two measures. This indicates that they are influenced by two different sets of factors. The mechanical properties of passive wall elements functionally connected in series with the contractile apparatus (series elasticity) is one factor influencing the relation between force development and shortening. The relative wall thickness of arteries also can influence these factors by controlling the effectiveness of outer medial layer in changing lumen dimensions. Collagen also is involved in this process in some manner as treatment of arteries with purified collagenase results in a progressive, linear reduction in active force development. Correlation of mechanical performance with contractile protein content of arteries has identified two important regulatory factors. Force development by arteries from different anatomical sites can be related to the myosin content of the sites. Changes in force development at a given site can be related to a change in the ratio of actin-to-myosin content at that site (as occurs in hypertension). Thus, the potential exists for numerous factors to contribute to the determination of mechanical performance of arterial smooth muscle.