Sr2+ activates cross-bridge phosphorylation and latch state in smooth muscle.
Sr2+ induced myosin phosphorylation and stress development in both skinned and K+-depolarized, Ca2+-depleted, intact swine carotid media. Although higher concentrations of Sr2+ than Ca2+ were required for phosphorylation and stress development, the dependence of stress on phosphorylation was the same in intact tissues. K+ depolarization in the presence of 5 mM Sr2+ produced a transient in phosphorylation (53.2 +/- 5.1% at 1 min, falling to a steady-state value of 21.7 +/- 2.0%) in Ca2+-depleted tissues in which intracellular stores were refilled with Sr2+. Stress developed without a transient (T1/2 = 0.70 min) to a steady state of 89.7 +/- 2.0% of the stress induced by K+ depolarization in the presence of 1.6 mM Ca2+ (K-PSS). Cross-bridge cycling rate as measured by isotonic shortening velocity was proportional to myosin phosphorylation throughout the contraction. When intracellular stores were not refilled with Sr2+, phosphorylation rose to a sustained value of 28.8 +/- 2.7% and stress developed slowly (T1/2 = 2.9 min) to a steady state of 95.9 +/- 1.5% K-PSS-induced stress. Therefore, an initial phosphorylation transient induced by intracellular Sr2+ release only accelerated stress development without significant effects on steady-state stress or phosphorylation (as was true for Ca2+- induced responses). We concluded that Sr2+ substitutes for Ca2+ in phosphorylation and regulation of the latch state in the swine carotid media.
Department of Physiology, School of Medicine, University of Virginia, Charlottesville 22908.
C M
CM
Hai
R A
RA
Murphy
D000818:Animals; D002122:Calcium Chloride / Q000494:pharmacology; D002339:Carotid Arteries / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D009218:Myosins / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D010766:Phosphorylation; D011188:Potassium / Q000494:pharmacology; D013324:Strontium / Q000494:pharmacology*; D013552:Swine
D010710:Phosphates; D009218:Myosins; C025700:strontium chloride; D002122:Calcium Chloride; D011188:Potassium; D013324:Strontium