Latch-bridge model in smooth muscle: [Ca2+]i can quantitatively predict stress.
Ca2+ concentration ([Ca2+])-dependent cross-bridge phosphorylation by myosin light chain kinase is postulated to be the primary regulator of stress development in smooth muscle. A four-state model of cross-bridge function, regulated only by [Ca2+]-dependent changes in myosin kinase activity, has been proposed to explain contraction and the latch state of smooth muscle (high force with reduced cross-bridge cycling and ATP consumption). A key test of this model is to determine whether changes in myoplasmic [Ca2+], per se, can quantitatively predict changes in myosin kinase activity, cross-bridge phosphorylation, and therefore force production. We find that changes in aequorin-estimated myoplasmic [Ca2+] can quantitatively predict the time course of phosphorylation and isometric stress production in response to stimulation with histamine and angiotensin II and during adenosine 3',5'-cyclic monophosphate-mediated relaxation when [Ca2+] is not changing rapidly. These results suggest that changes in myoplasmic [Ca2+] and activation of myosin light chain kinase may be sufficient to explain both contraction and relaxation of agonist stimulated swine carotid arterial smooth muscle.
Rembold
C M
CM
Department of Internal Medicine, University of Virginia Health Science Center, Charlottesville 22908.
Murphy
R A
RA
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002339:Carotid Arteries / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D015879:Myosin Subfragments / Q000378:metabolism; D010766:Phosphorylation; D013314:Stress, Mechanical; D013552:Swine
D015879:Myosin Subfragments; D002118:Calcium