Steady-state dependence of stress on cross-bridge phosphorylation in the swine carotid media.
Tonic contractions of the swine carotid media are typically characterized by initial transients in myoplasmic [Ca2+] and cross-bridge phosphorylation followed by force maintenance with reduced intracellular [Ca2+] and cross-bridge phosphorylation ("latch"). The presence of effective mechanisms in the carotid media to limit steady-state myoplasmic [Ca2+] and cross-bridge phosphorylation to modest increases over resting values has limited experimental attempts to determine the dependence of active stress (force/tissue cross-sectional area) on cross-bridge phosphorylation. In this study, we employed stimulation protocols that combined effective contractile agonists with inhibitors of Ca2+ extrusion or sequestration to achieve high steady-state levels of cross-bridge phosphorylation (up to 60%). Increases in cross-bridge phosphorylation from 30 to 60% were not associated with significant increases in stress in agreement with the predictions of Hai and Murphy [Am. J. Physiol. 254 (Cell Physiol. 23): C99-C106, 1988] four-state cross-bridge model for the carotid media. Thus cross-bridge phosphorylation may suffice to determine force generation in vascular smooth muscle if both phosphorylated and dephosphorylated attached cross bridges (or latch bridges) contribute to active stress.
Di Blasi
P
P
Department of Physiology, University of Virginia, Charlottesville 22908.
Van Riper
D
D
Kaiser
R
R
Rembold
C M
CM
Murphy
R A
RA
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002339:Carotid Arteries / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D007700:Kinetics; D008094:Lithium / Q000494:pharmacology; D008536:Meglumine / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D009218:Myosins / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism*; D010766:Phosphorylation; D012044:Regression Analysis; D013314:Stress, Mechanical; D013552:Swine
D007211:Indoles; D010710:Phosphates; D008536:Meglumine; D006632:Histamine; D008094:Lithium; D009218:Myosins; D000252:Calcium-Transporting ATPases; D002118:Calcium; C000543:cyclopiazonic acid