ENERGETICS OF CROSSBRIDGE PHOSPHORYLATION AND CONTRACTION IN VASCULARSMOOTH-MUSCLE

Ca2+-dependent crossbridge phosphorylation is the primary mechanism go verning crossbridge cycling in smooth muscle. A four-state crossbridge model in which phosphorylation is the only proposed regulatory mechan ism was successful in predicting the mechanical properties of the swin e carotid media including latch (sustained force with reduced crossbri dge cycling). This model also predicts that the ATP consumption of cro ssbridge phosphorylation is approximately equal to that of crossbridge cycling and that ATP consumption will rise hyperbolically with increa ses in steady-state force. This review shows these predictions to be c onsistent with the available energetics data for the carotid media. Th e absolute energetic cost of covalent regulation is modest and less th an the energy savings associated with latch. However, covalent regulat ion should reduce the total mechanical efficiency of smooth muscle rel ative to striated muscle.